,,glass ---------------------------------------- -------------------------------- ,reprinted ,june1 #aiah4 ,reprinted ,june1 #aiai4 ---------------------------------------- -------------------------------- ,illustration3 ,,an ,,old ,,glass ,,house1 ,a4,d4 #agij ,frontispiece ---------------------------------------- -------------------------------- ,,pitman',s ,,common ,,commodities ,,and ,,industries ,,glass ,,and ,,glass ,,manufacture ,,by ,,percival ,,marson ,,consultant ,,upon ,,refractory ,,materials1 ,,etc41 ,,honours ,,and ,,medallist ,,in ,,glass ,,manufacture4 ,,london ,,sir ,,isaac ,,pitman ,,sons1 ,,ltd41 #a ,,amen ,,corner1 ,e4,c4#d ,,bath1 ,,melbourne ,,and ,,new ,,york ---------------------------------------- -------------------------------- ,,printed ,,by ,,sir ,,isaac ,,pitman ,,sons1 ,,ltd41 ,,london1 ,,bath1 ,,new ,,york ,,and ,,melbourne ---------------------------------------- -------------------------------- ,,preface ,who is not acquainted with glassware in some form or other8 ,from the early days of the ,ancient ,egyptians the art of glassmaking was known1 and it is now one of our most important industries1 supplying as it does many articles for our common domestic use and convenience4 ,glass windows have introduced comfort and convenience into every home2 for by their means light is admitted into our dwellings without the wind1 rain and cold1 and we enjoy the blessings of the one without the inconveniences of the others4 ,the purposes for which glass can be used are manifold2 and in domestic articles it contributes largely to our cleanliness and health4 ,in the use of spectacles1 table glass1 mirrors1 bottles1 and many other goods our dependence upon glass becomes very evident4 ,the degree of proficiency attained in the manufacture of glass is still more remarkable when we consider the various kinds of glassware used in physical1 chemical1 astronomic1 medical1 and other scientific investigations4 ,many of the wonderful results of the present times would not have been attained without the aid of glass in supplying the needs of our scientific investigators4 ,before ,august1 #aiad1 few people realised the important part glass occupies in the production of war munitions4 ,the importance of optical glasses for telescopes1 gun sights1 and microscopes is well known4 ,again1 glass plays an essential part in every ship1 locomotive1 motor-car1 aeroplane1 and coal mine1 and if defective glasses were supplied there would be a great loss in our industrial efficiency4 ,the manufacture of high explosives or special steels could not be carried on without the supplies of laboratory glassware to enable the chemist to carry out his delicate tests4 ,upon the outbreak of the present war our supplies of certain types of glassware were not made in ,great ,britain1 but imported from abroad1 and it was owing to the energy and enterprise of a ,scottish glass manufacturer1 with some assistance from a well-known scientist1 that a start was made in making these much-needed goods1 and what might have been a serious crisis was averted4 ,professor ,herbert ,jackson and the ,institute of ,chemistry placed at the disposal of glass manufacturers numerous formulas for the special glasses that were urgently required1 and later on this work was recognised by the ,government2 and now the investigations are being continued by a committee1 with the assistance of the ,government1 under the control of the ,ministry of ,munitions4 ,this committee is now rendering the greatest assistance to manufacturers in the general development of the glass trade and the reclamation of the ground lost in previous years4 ,there is now every hope that ,britain may raise again to eminence and perfection this very important industry of glassmaking4 ,one of the chief objects of this volume is to supply within a small practical treatise the general available information upon glass manufacture1 much of which1 although familiar to many manufacturers or those engaged in glass works1 will be of great assistance to those who are commencing a study of this very interesting and complex subject4 ,few people have any idea of the vast and enormous trade done on the ,continent in the manufacture of glassware for export to ,great ,britain and ,british ,possessions abroad1 and on this account it is essential that so important a subject as glass manufacture should form some part in the technical education of our universities and trade schools1 so that a section of the rising generation may be taught to understand the manufacture of such a necessary commercial product1 and assist in recapturing the trade from the ,continental glass works in supplying our needs4 ,that some progress has been made along these lines is evident by the establishment at ,sheffield ,university of a school in ,glass ,technology1 and it is to be hoped that similar schools will be established in other centres1 staffed by capable instructors and supported by the co-operation of the glass manufacturers4 ,the author gives in an ,appendix the literature accessible to those who wish for further information upon the subject1 and trusts that1 in the presentation of these notes1 in response to the demand for such a book1 a useful purpose will have been served by introducing the first principles of glass manufacture to those interested4 ,it affords me great pleasure to acknowledge the valuable aid that has been rendered me by ,mr4 ,s4 ,n4 ,jenkinson1 ,professor ,herbert ,jackson1 and ,mr4 ,frederick ,carder1 to whom ,i am much indebted4 ,my thanks are also due to the following firms3 ,messrs4 ,melin ,co41 ,crutched ,friars2 ,the ,hermansen ,engineering ,co41 ,birmingham2 ,the ,glass ,engineering ,co41 ,edinburgh2 and ,banks ,co41 ,edinburgh1 who have kindly supplied me with illustrations4 ,,percival ,,marson4 ,,craigentinny1 ,,edinburgh4 ---------------------------------------- -------------------------------- ,,contents ------- ,,chap4 ,,page ,,preface ,v ,i4 ,,history #a ,,ii4 ,,the ,,chemistry ,,of ,,glass-,,making ,,and ,,the #d ,,materials ,,used ,,iii4 ,,the ,,chemical ,,and ,,physical ,,properties ,,of #ae ,,glass ,,iv4 ,,the ,,composition ,,of ,,the ,,different ,,kinds #bd ,,of ,,glass ,v4 ,,coloured ,,glass ,,and ,,artificial ,,gems #bh ,,vi4 ,,decolorizers #cb ,,vii4 ,,the ,,refractory ,,materials ,,used #cf ,,viii4 ,,glass ,,house ,,furnaces #dc ,,ix4 ,,glass-,,melting ,,pots ,,and ,,their ,,manufacture #ei ,x4 ,,lehrs ,,and ,,annealing #ga ,,xi4 ,,the ,,manipulation ,,of ,,glass--,,glassmakers' #gf ,,tools ,,and ,,machines ,,xii4 ,,crown1 ,,sheet1 ,,and ,,plate ,,glass #hi ,,xiii4 ,,tube1 ,,cane1 ,,and ,,chemical ,,glassware #if ,,xiv4 ,,optical ,,glass #ajd ,,xv4 ,,decorative ,,glassware #ajh ,,xvi4 ,,english ,,and ,,foreign ,,methods ,,of ,,glass #aah ,,manufacture ,,compared ,,appendix #abc ,,index #abe ---------------------------------------- -------------------------------- ,,list ,,of ,,illustrations ------- ,,page ,,an ,,old ,,english ,,glass ,,house1 ,a4,d4 #agij ,frontispiece ,,horizontal ,,cracking-,,off ,,machine #a ,,interior ,,view ,,of ,,an ,,english #dd ,,glass-,,melting ,,furnace ,,exterior ,,view ,,of ,,an ,,english #df ,,glass-,,melting ,,furnace ,,siemens ,,siegbert ,,regenerative ,,glass-,,melting ,,furnace-- ,,fig4 ,a4 ,,cross ,,section #dh ,,fig4 ,b4 ,,sectional ,,plan #di ,fig4 ,c4 ,,sectional ,,elevation #ej ,a ,,modern ,,glass ,,house4 ,,hermansen',s #eb ,,continuous ,,recuperative ,,glass-,,melting ,,furnace1 ,,covered ,,pot ,,type ,,hermansen',s ,,continuous ,,recuperative #ec ,,glass-,,melting ,,furnace1 #h-,,pot ,,type ,,hermansen ,,furnace-- ,,fig4 ,a4 ,,section ,,through ,,gas ,,producer #ed ,,fig4 ,b4 ,,cross ,,section ,,through ,,gas #ee ,,producer ,,fig4 ,,sectional ,,plan #ef 8,,the ,,harlington0 ,,bottle-,,making ,,machine #gi ,,glass ,,worker',s ,,chair #ha ,,glassware ,,blown ,,in ,,moulds1 ,,fig4 ,a4 ,,and #he ,b4 ,,vertical ,,cracking-,,off ,,machine #hg ,,four ,,stages ,,in ,,crown ,,glass ,,making 7,a1 ,b1 #ij ,c1 ,d7 ,,six ,,stages ,,in ,,sheet ,,glass ,,making 7,a1 ,b1 #ia ,c1 ,d1 ,e1 ,f7 ,,machine ,,for ,,smoothing ,,bottoms ,,of #aaj ,,tumblers ,,glass ,,engraving #aac ---------------------------------------- -------------------------------- ,,glass ,,and ,,glass ,,manufacture ------- ,,chapter ,i ,,history ,the discovery of making glass is attributed to the early ,phoenicians4 ,pliny relates that certain mariners who had a cargo of soda salt1 having landed on the banks of a river in ,palestine1 started a fire to cook their food1 and1 not finding any stones to rest their pots on1 they placed under them some lumps of the soda from their cargo4 ,they found that the heat of their fire had melted the soda and fused it with the sand of the river bank1 producing a transparent glass4 ,the natives in the vicinity where this discovery was made in process of time carried on the practice of fusing sand with soda and other materials to make glass1 until they succeeded in improving and bringing the art to a high degree of excellence4 ,discoveries amongst the ruins of ,pompeii and ,herculaneum present some first-rate examples of the skill attained by the ancients in glassmaking3 glass was found to have been used there1 admitting light into dwellings in the form of window glass4 ,the ancient ,egyptians have left us many distinct proofs that glassmaking was practised in ,egypt4 ,at the same time1 the glazing of pottery was also carried out1 proving that they knew the mode of mixing1 fusing1 and melting the proper ingredients for glassmaking4 ,among the tombs of ,thebes many specimens of glass and glazed pottery beads have been found1 which suggests a date about #c1ejj years ago4 ,from the ,egyptians1 the ,greeks and ,romans acquired the art of glassmaking1 which in ,nero's time was so highly developed that clear crystal glasses were produced in the form of drinking cups and goblets1 which superseded the use of gold cups and were much prized by the ,emperor in those days4 ,many specimens of old ,roman glass discovered have been preserved in the ,british ,museum1 and1 although many valuable pieces have been lost by disintegration and collapse due to the influence of years of exposure1 there still remain some very fine examples which show that the ,romans were highly skilled in glassmaking4 ,one of the finest examples of the work of the ancient ,romans in glassmaking is the ,portland ,vase1 which was unearthed near ,rome4 ,this is an ornamented vase showing white opaque figures upon a dark blue background4 ,the white opal appears to have been originally cased all over the blue and the beautiful figures carved out in cameo fashion1 with astonishing patience and skill upon the part of the operator4 ,the ,venetians and ,muranians followed the ,romans in the art1 and examples of old ,venetian glassware show rare skill and ingenuity4 ,to the ,venetians belongs the honour of first making glass at a cost to allow of its being more generally used1 and they also introduced the art of making window glass and drinking vessels into this country4 ,jacob ,verzelina1 a ,venetian1 introduced such glassmaking into ,england1 working at a factory in ,crutched ,friars1 ,london1 between #aeej and #aeeg1 where he made window glass1 afterwards carrying on similar work in other places about the country until his death in #afjf4 ,not until #afai were glass works started in the neighbourhood of ,stourbridge4 ,there we find some remains of a factory worked by ,tyzack about that date in making window glass in the village of ,oldswinford4 ,that ,stourbridge should have been selected as one of the early centres for glassmaking is probably due to the presence in that locality of the so necessary and important to glass manufacturers in building their furnaces and pots1 and the coal used for maintaining the fires for melting their glass4 ,stourbridge was known for a long time before this as a centre for the mines producing 1 and eventually this clay was adopted for making glass-house pots2 now many other sources are available for these fire-clays4 ,much of the antiquity of the glassmaking of ,england is hidden in the neighbourhood of ,stourbridge1 and the writer has himself found a few antique specimens of old green devitrified window glass embedded in the subsoil of some fields near ,oldswinford1 probably relics of the ,huguenots1 who practised and extended the art of glassmaking in that district4 ,other important centres for glassmaking now are ,york1 ,london1 ,manchester1 ,edinburgh1 ,newcastle1 and ,birmingham2 but1 although glassmaking has reached a high degree of excellence in this country1 there is nothing yet comparable with the extensive factories which exist abroad4 ,the conservatism of many ,english manufacturers1 and the adverse influence of the ,glass ,makers' ,society1 considerably restrict the progress of this trade compared with the broad and progressive manner in which it is carried on abroad4#a ,footnote #a3 ,see article 8,trade ,unionism10 in last chapter4 ---------------------------------------- -------------------------------- ,,chapter ,,ii ,,the ,,chemistry ,,of ,,glass-,,making ,,and ,,the ,,materials ,,used ,the term 8glass10 in a general sense1 is applied to the hard1 brittle1 non-crystalline1 transparent1 opaque or translucent vitreous substance which results from fusing silica with active mineral solvents or fluxes1 such as the alkalies1 earthy bases1 or metallic oxides4 ,silica exists in great abundance1 in a free natural state1 in the form of flints1 quartz1 and sand2 and in the latter form it is now most generally used for glassmaking4 ,when sand alkali and lead oxide are heated together to a high temperature1 the sand is dissolved by the solvent action of the fused alkali and lead oxide until the whole becomes a molten mass of glass4 ,the solvent action of the alkalies1 soda potash or lead oxide1 is very energetic whilst being heated1 and the mass boils with evolution of gases until1 at last1 the solution1 becoming complete1 settles down to a clear quiescent molten liquid metal1 which is quite soft and malleable1 after the nature of treacle4 ,in this condition it is ready for working4 ,the time and temperature necessary for melting such mixtures vary according to the proportions and composition of the ingredients4 ,silica1 combined with alumina and other oxides1 is freely distributed in nature in the form of clays1 granites1 and feldspars1 which are also available for use in glassmaking4 ,originally glass was made by using crushed and ground flint stones as the source for the silica3 hence is derived the old name of 8flint0 glass2 but now the large extensive deposits of white sand present a much more convenient and less expensive source1 and sand has become universally used4 ,fine white sand is obtained from ,fontainebleau1 near ,paris2 other sources are ,lippe1 ,lynn1 ,aylesbury1 ,isle of ,wight1 ,holland1 and ,belgium4#b ,these are the sources preferred by crystal glass manufacturers and makers of fine quality glass1 such as chemical ware pressed glass1 tube1 cane1 and medical bottles1 on account of their greater purity4 ,the commoner varieties of sand from ,reigate and ,bagshot and even red sand are being used in the manufacture of the lower grades of glass such as beer bottles and jam jars1 where a greater latitude in the chemical impurities present is permissible4 ,only the best and purest silica sands are used for making cut crystal and optical glasses4 ,in these trades the sand is always cleaned by washing it in water to clear it from any salt1 chalk1 or other impurities which may possibly be present4 ,the sand1 after washing1 is heated to redness1 or 8burnt10 in order to burn off any organic or vegetable matter1 and when cold it is sifted through a fine screen to take out any coarse grains or lumps4 ,in this prepared state1 the sand is ready for weighing out into the proportions desired for mixing with the other materials1 and is stored for use in covered wooden compartments situated in or near the mixing rooms1 along with the other materials which may be used in the glass mixtures4 ,footnote #b3 ,see 8,british ,glass ,sands0 7,boswell71 8,british ,glassmaking ,sands0 7,peddle72 papers read at the third meeting1 ,society of ,glass ,technology1 ,sheffield1 for further information4 ,the alkalies1 potash or soda1 or a mixture of both1 are commonly used in making glass in the form either of carbonates1 sulphates1 or nitrates4 ,the soda and potash silicates form very fusible glasses1 but they are not permanent1 being soluble in water2 therefore they cannot be used alone4 ,in making glassware for domestic use1 other bases1 such as lead oxide1 barium1 or lime1 have to be added to form more insoluble combinations with the silica or sand4 ,carbonate of ,potash or ,pearlash1 which before the war was imported into this country by glass makers from ,stassfurt1 is much prized by crystal glass makers on account of the colourless silicate it forms when fused with the best white sand4 ,it is now very expensive and difficult to get1 and is less used on this account4 ,potash carbonate is very hygroscopic and absorbs much moisture from the air2 therefore it is necessary to keep it within sealed chests while in store4 ,potash and soda each have an influence upon the colour of the resulting glasses in which they are respectively used4 ,the potash silicate gives better and clearer glasses than the soda silicate4 ,carbonate of ,soda1 or ,soda ,ash1 is now more generally used4 ,being a less expensive form of alkali1 it constitutes a base in most of the commoner varieties of glassware4 ,carbonate of soda is manufactured in ,england from common salt1 of which there are large deposits in the ,midlands4 ,this common salt1 or chloride of sodium1 is treated chemically and converted into the carbonate1 in which form it is supplied to the glass manufacturers as soda ash4 ,sulphate of ,soda 7,salt ,cake7 is the form of alkali used in window and bottle glassmaking4 ,in mixtures containing sulphate of soda it is necessary to use a small proportion of carbon in some form1 such as charcoal or coal1 in order to assist the decomposition of the salt and the formation of the sodium silicate4 ,sulphate of soda is used in this class of glassware on account of its cheapness4 ,glasses made from sulphate of soda mixtures are not so clear and colourless as those in which the source of alkali is potash or soda carbonate4 ,on this account1 the best crystal glasses cannot be made from sulphate of soda4 ,potash ,nitrate 7,saltpetre7 is used in glass mixtures to oxidise the molten metal and improve the colour of the glass4 ,in fusing it disengages oxygen gas1 which purifies the glass while melting1 and assists the decolorizers in their action by keeping up an oxidising condition within the molten mass4 ,sodium ,nitrate1 or ,chili ,nitre1 is the corresponding soda salt to potash nitre4 ,it is much cheaper1 but less pure2 it has a similar but not nearly so powerful an oxidising action in the glass as potash nitre4 ,it is exported from ,chili1 where it exists naturally in a crude state as 8,caliche10 from which the nitrate is refined by recrystallisation4 ,boric ,acid acts as an acid in glass1 as does silicic acid4 ,it renders glass more fusible and brilliant2 it has a searching action upon the colourising properties of certain metallic oxides when they are dissolved in the glass4 ,it is an expensive ingredient1 but is considerably used in optical and special chemical glassware in replacing a portion of the silicates ordinarily used and forming borates4 ,it cannot be used in large amounts1 as an excess produces glass of a less stable nature4 ,borax1 or ,borate of ,soda1 consists of boric acid combined with soda4 ,it is a very useful glassmaking material and is an active fluxing agent4 ,if used in excess in glass mixtures it causes considerable ebullition1 or boiling of the metal4 ,in moderate proportions it is used in the manufacture of enamels for glass1 as it helps to dissolve the colorific oxides and diffuse the colouring throughout the enamel mass4 ,tincal1 and ,borate of ,lime1 are other forms in which borates may be introduced into glass4 ,carbonate of ,lime1 ,limespar1 ,limestone1 ,paris ,white1 or ,whitening are all forms of ,calcium ,carbonate4 ,it is an earthy base and is added to the simple alkaline silicates and borates to form insoluble combinations or double silicates of soda and lime4 ,by the use of lime1 glasses are rendered more permanent and unchangeable when in use4 ,lime forms a very powerful flux at high temperatures4 ,the quantity used must be carefully regulated according to the proportion of other bases present2 otherwise an inferior or less stable glass may be produced4 ,in excess it causes glass to assume a devitrified state4 ,dolomite is a ,magnesium ,limestone1 and is a natural stone which is available for use in making glass in tank furnaces4 ,fluorspar1 or ,fluoride of ,lime1 is used in giving opacity and translucency to glass4 ,it can only be used in small amounts1 as the presence of any large proportion attacks the clay of the pots1 causing serious damage by the sharp cutting chemical action due to the evolution of fluorine gas4 ,phosphate of ,lime is another material which produces opacity and translucency1 but does not seriously attack the pots4 ,bone ash is a form of phosphate of lime1 and is procured by calcining bones until all organic matter is consumed4 ,carbonate of ,barium1 or ,witherite1 is a very heavy1 white powder1 and is a form of earthy base available for use in glassmaking4 ,it can be used to replace lime1 with similar results4 ,by replacing other elements in the glass which are of lower density1 barium can be used to increase the density of glass4 ,like lime it is a very powerful flux in glass at high temperatures4 ,it gives increased brilliancy and little coloration4 ,for this reason it is very useful in the manufacture of pressed glassware1 giving a glass which leaves the moulds with better gloss than is found to be the case with lime glasses4 ,magnesia and ,strontia are other bases which are less used in glassmaking4 ,zinc ,oxide is a base used in the manufacture of many optical glasses4 ,with boric acid it gives silicates of a low coefficient of expansion and special optical values4 ,used with cryolite1 it forms a very dense opal suitable for pressed ware4 ,it is rather more expensive than the other bases used4 ,cryolite is a natural opacifying ingredient used in making opal glasses4 ,it consists of a combination of the fluorides of aluminium and sodium1 and is one of the most active fluxes known to glass and enamel makers4 ,its cutting chemical attack on the pots is very intensive4 ,it is imported from ,greenland4 ,an artificially manufactured form of cryolite is known1 which is a little cheaper than the natural variety and gives similar results in opacifying glass4 ,alumina4 ,this is sometimes present to a small extent in glass makers' sands4 ,as such it is not a dangerous impurity4 ,it exists in combination with silica and potash to a large extent in feldspars1 china clays1 and granites4 ,alumina1 when used1 has a decided influence upon the viscosity and permanency of glass4 ,in large proportions it noticeably diminishes the fusibility of glass1 and makes it more or less translucent4 ,owing to the refractory nature of alumina it is with difficulty that it can be diffused in alkaline silicates1 borates1 or lead silicates2 consequently any considerable proportion present in glass may cause cords or striae1 which are objectionable defects in the glass4 ,oxide of ,lead4 ,red ,lead1 or ,minium1 is much used in the manufacture of enamels1 table glassware1 and heavy optical glass4 ,it gives great brilliancy and density to all glasses in which it is used1 but if used in excess the glass is attacked readily by mineral acids and becomes unstable4 ,red lead is a powerful flux1 even at low temperatures1 and forms the chief base in making best crystal ware and enamels4 ,the red oxide of lead used by glass manufacturers is a mixture of the monoxide and peroxide4 ,glass manufacturers1 in buying red lead1 should realise that it is the peroxide present which is the active oxidising agent1 and that at least #bg per cent4 should be present4 ,a dull1 dark red oxide shows a low percentage of peroxide2 a bright orange red a high percentage4 ,impure red oxides of lead may be adulterated with barytes1 finely divided metallic lead1 or added water4 ,such impure varieties should be avoided4 ,the red oxide of lead is preferred to the other oxides and forms of lead for glassmaking1 on account of its greater oxidising action1 which is desirable in producing crystal glassware4 ,tin ,oxide and ,antimony ,oxide are used as opacifiers4 ,when used they generally remain suspended in a finely divided form in the glass4 ,used in small quantities they have a favourable influence in the development of ruby-coloured glasses4 ,manganese1 ,arsenic1 and ,nickel ,oxides are used in glassmaking as 8decolorizers10 which will be treated in a later chapter4 ,cullet4 ,in all glasses a proportion of 8cullet10 or broken glass scrap1 is used4 ,this cullet is usually of the same composition as the glass mixture or 8batch40 ,the use of cullet facilitates the melting1 and assists in giving homogeneity to the resultant glass by breaking up the cords and striae which tend to develop in most glasses4 ,in the commoner varieties of bottle glass ,basalt and other igneous rocks are crushed and used4 ,these are naturally occurring silicates containing lime1 alumina1 alkalies1 iron1 and other elements in varying proportions4 ,they are used more on account of their cheapness1 and produce dark1 dirty-coloured glasses1 which in the case of common bottles are not objected to4 ,in some instances iron1 manganese or carbon is added to produce black bottle glass4 ,of the various silicates used in glassmaking1 the silicate of alumina is the most refractory4 ,the silicates of lime and barium are rather refractory1 but under a strong heat and in the presence of other silicates they can be readily formed4 ,the silicates of the alkalies1 lead1 and many of the other metals are formed at much lower temperatures4 ,in the case of the silicate of iron1 manganese1 or copper1 a strong affinity is shown between the metal and the silica1 and a black or dark-coloured slag with a very low melting point is formed4 ,such slags are very active in corroding the masonry and pots of the furnace4 ,no single silicate is entirely free from colour4 ,each gives a slight distinctive coloration1 the lead silicate being yellowish and the soda silicate greenish1 but by the judicious mixture of different silicates and the use of decolorizers1 such as manganese1 nickel1 etc41 compound silicates are obtained1 giving less perceptible colours or crystal effects4 ,in optical glassmaking the use of the ordinary decolorizers is not permissible1 and the purity of the materials used becomes the most important factor4 ,the raw mixture of the various materials used in making glass is termed a 8batch40 ,the mixing is usually done by hand1 but in many cases mechanical batch mixers are used4 ,if the mixing is done by hand1 the materials are first weighed out in their correct proportions by means of a platform weighing-machine4 ,as they are weighed out1 one by one1 they are introduced into a rectangular wooden arbour or box1 large enough to hold the whole unit weight of the batch and allow of its being mixed and turned from side to side4 ,the batch is then sieved1 and all the coarse materials reduced or crushed to a size not coarser than granulated sugar4 ,by sieving and turning the batch several times a thorough mixture of the ingredients is obtained4 ,a few ounces of manganese dioxide are then added1 according to the unit weight of the batch weighed out1 and the proportion of decolorizer necessary2 which varies according to the heat of the furnace and the amount of the impurities present4 ,the whole batch is then put into barrels and conveyed to the glass house1 where the furnace is situated4 ,here it is tipped into another arbour or box in a convenient position near to the melting pot1 and1 a proportional quantity of 8cullet0 being added1 the mixture is then ready for filling into the pots4 ,the stopper of the pot mouth is taken away and placed aside1 and a man shovels the mixture or batch into the hot pot until it is full4 ,he then replaces the stopper1 and1 after a few hours1 when the first filling has melted and subsided1 another filling of batch into the pot takes place until it becomes full of glass metal in its molten state4 ,the batch melts with considerable ebullition1 owing to the chemical reactions taking place under the heat of the furnace1 giving off at the same time large quantities of gas4 ,by the evolution of these gases the batch shrinks in volume so that it becomes necessary to fill a pot more than once with the batch before it becomes full of molten metal4 ,the capacity of the pots varies between #bej and #a1bjj kilogrammes1 according to the type of glass and nature of the goods made4 ,much care is required in mixing and sieving batches containing lead and other poisonous ingredients1 to prevent the inhalation of the dust by the mixer4 ,therefore1 where such materials are used1 exhaust fans and ventilating ducts should be provided and fitted in the mixing rooms4 ,a proper respirator should be worn by the mixer in charge to prevent any absorption into his system of the poisonous dust4 ,cases of poisoning are not unknown1 but these are due to gross carelessness4 ,a small regular weekly dose of ,epsom salts should be taken by the mixers who have to prepare lead batches4 ,this salt tends to remove any lead salts absorbed in the system by converting them into insoluble lead sulphate4 ---------------------------------------- -------------------------------- ,,chemical ,,formulae ,,and ,,molecular ,,weights4 ,molecular ,materials4 ,formulae4 ,weight4 ,alumina ,al#b,o#c #ajb ,antimony ,oxide ,sb#b,o#c #bhg ,arsenic ,as#b,o#c #aig ,bismuth ,oxide ,bi#b,o#c #dfh ,boric ,acid ,h#c;,,bo#c #fb ,borax ,na#b;,b#d,o#gaj;,h#b,o #chb ,calcined ,borax ,na#b;,b#d,o#g #bjb ,calcined ,potash,k#b;,,co#c #ach ,carbon ,c #ab ,carbonate of ,ba,c,o#c #aig ,barium ,carbonate of ,mg,c,o#c #hd ,magnesia ,china ,clay #b,si,o#b;,al#b,o#cb;,h#b,o #beh ,chrome ,oxide ,cr#b,o#c #aec ,cobalt ,oxide ,co#b,o#c #aje ,copper ,oxide ,cu#b,o #adc 7,red7 ,copper ,oxide ,cu,o #gi 7,black7 ,cryolite #f,na,f,al#b;,f#f #baj ,dolomite ,ca,o,mg,o#b;,,co#b #ahd ,fluorspar ,ca,f#b #gh ,gold ,chloride ,au,cl#cb;,h#b,o #cci ,iron ,oxide ,fe#b,o#c #afj ,lime ,ca,o #ef ,lime ,spar ,ca,c,o#c #ajj ,manganese ,oxide,mn,o#b #hg ,nickel ,oxide ,ni,o#b #ge ,nitrate of ,soda,na,n,o#c #he ,phosphate of ,ca#c7,,po#d7b #caj ,lime ,potash ,k#b;,,co#c7b;,h#b,o7 #agd ,carbonate ,potash ,felspar #f,si,o#b;,al#b,o#c,k#b,o #eef ,red ,lead ,pb#c,o#d #fhc ,saltpetre ,,kno#c #aja ,sand ,si,o#b #fj ,soda ,carbonate ,na#b;,,co#c #ajf ,sodium ,fluoride,na,f#c #fa ,sulphate of ,na#b,,so#d #adb ,soda ,tin ,oxide ,sn,o#b #aej ,uranium ,oxide ,,uo#b #bgb ,zinc ,oxide ,zn,o #ha ---------------------------------------- -------------------------------- ,,chapter ,,iii ,,the ,,chemical ,,and ,,physical ,,properties ,,of ,,glass ,the main essential and peculiar property of glass is its transparency4 ,when subjected to a gradually increasing temperature1 glass becomes softened1 and whilst hot it is plastic1 ductile1 and malleable1 in which state it can be cut1 welded1 drawn1 or pressed4 ,a thread of glass can be drawn so thin and fine that it can be twisted and bent to a remarkable extent1 showing that glass is flexible4 ,the above properties shown by glass while softened under heat permit it to be shaped and formed by a variety of methods1 so that in the manufacture of the different kinds of glass we find goods pressed1 blown1 drawn1 moulded1 rolled and cast from the hot metal4 ,upon cooling1 the form given to them is retained permanently4 ,another property of glass is its conchoidal fracture and liability to crack under any sudden change of temperature4 ,advantage is taken of this peculiarity in dividing or cracking apart glass when necessary1 during the stages of the manufacture of any glass article4 ,illustration3 ,by permission of ,melin ,co4 ,,horizontal ,,cracking-,,off ,,machine ,if a glass worker1 in making an article of glass1 desires to detach or cut apart certain sections1 he applies a cold wet substance1 such as an iron file wetted with water1 to any portion of the hot glass1 which causes it to fracture at the point of contact with the cold metal1 and a slight jar is then sufficient to break the two portions apart4 ,this method of chilling heated glassware to divide it is applied in the mechanical process of cutting up the long cylindrical tubes of glass into short sections for use as miners' safety lamp chimneys4 ,wherever it is desired to cut them through1 a narrow section or line round the cylinder is first heated by a sharp1 hot pencil of flame projected from a burner against the rotating cylindrical tube of glass at equidistant short sections1 and the divisions chilled by contact with a cold1 steel point1 or the heated area may be gently scratched with a diamond point1 when a clean1 sharp fracture results exactly where the chill or scratch has been applied and spreads round the whole circumference in a circle1 giving neat1 clean-cut divisions4 ,in cutting narrow tube and cane1 the fracture caused in the structure of the glass by scratching its surface with a steel file or diamond is sufficient to cause it to break apart without the application of heat4 ,a piece of hot glass will weld on to another piece of hot glass of similar composition4 ,the glass maker uses this method of welding for sticking handles on to jugs1 etc41 during the process of making table glassware4 ,the density of glass varies according to its composition4 ,certain classes of lead and thallium glass for optical work are of very high density4 ,the specific gravities of such glasses may vary from #cj to well over #dj4 ,in soda-lime glasses the density is less and approaches #bd4 ,ordinary crystal glass approximates to a specific gravity of #ca4 ,the elasticity and thermal coefficient of expansion of glass can be regulated within normal limits4 ,glasses are now manufactured which can be perfectly sealed to copper1 iron1 nickel1 and platinum wires4 ,glass1 if kept heated for any length of time at a temperature just short of its softening or deformation point1 becomes devitrified and loses its transparency1 becoming opaque and crystalline4 ,in this state it has much of the nature of vitreous porcelain and is totally different to manipulate1 being tough and viscid on further heating4 ,this devitrified state may occur during glassmaking1 where the metal is allowed to remain in the pot or tank furnace for a considerable time under low temperature4 ,small stars or crystals first develop throughout the glass and continue to grow until it becomes a stony1 white1 opaque1 vitreous mass4 8,raumur's ,porcelain0 is a glass in a devitrified state1 and is used for pestles and mortars1 devitrified glass being less brittle than ordinary glass and similar to vitrified porcelain4 ,glass can be toughened to an extent which is surprising4 ,bastie's process consists of plunging the finished glass article whilst hot into a bath of boiling oil1 which toughens the glass so much as to make it extremely hard and resistant to shocks1 losing most of its brittle nature4 ,strong plates of glass are produced by a process of toughening under pressure4 ,these plates of glass are used for ship porthole lights and in positions where great strength is required4 ,toughened or hardened glass is of great value in the production of miner's lamp glasses and steam-gauge tubing4 ,glass1 when hardened1 is difficult to cut even with the diamond1 and difficulty is experienced in finding suitable means to cut it into shapes to suit commercial requirements4 8,prince ,rupert drops10 or tears1 exhibit the state in which unannealed glass physically exists4 ,these are made as a curiosity by dropping a small quantity of hot metal from the gathering-iron into a bath of water and then taking the pear-shaped drops out quickly4 ,these pear-shaped drops of glass will stand a hard blow on the head or thicker portion without breaking1 but1 if the tail is pinched off or broken1 the whole mass crumbles and falls to powder4 ,this well illustrates the latent stresses or strains apparently in a state of tension and thrust within the structure of unannealed glass4 ,glass is not a good conductor of heat4 ,this accounts for the necessity of slow cooling or annealing glassware1 and also applies when re-heating glass1 which must be done slowly and evenly to allow time for the conduction of the heat through the mass gradually4 ,glass is a non-conductor of electricity1 and is used to a considerable extent in the electrical trades for insulation purposes4 ,most glasses are attacked slightly1 but not readily1 by water and dilute mineral acids4 ,continued exposure to a moist1 humid atmosphere causes slight superficial decomposition1 according to the stability and chemical composition of the glass4 ,old antique specimens of glass show the superficial decomposition caused by long continuous exposure to atmospheric moisture4 ,many antique specimens have been known to collapse instantly upon being unearthed4 ,the first change in antique glass is exhibited by a slight iridescence forming on the surface1 gradually increasing towards opacity afterward disintegration sets in1 until it finally collapses or crumbles to powder4 ,glasses high in lead are readily attacked by the acid vapours met with in the atmosphere1 but the harder soda-lime glasses are more resistant4 ,an excess of boric acid1 soda1 or potash also renders glass subject to disintegration and decay4 ,hydrofluoric acid attacks all silicate glasses1 liberating silicon fluoride4 ,use is made of this acid reaction in decorating glasswares in 8,etching10 by exposing the surface of glass to the fumes of hydrofluoric acid gas in some form4 ,the most permanent glasses are those containing the highest proportion of silica in solution1 but the available heat necessary to decompose such highly silicious mixtures is limited by the present known refractory materials which can be procured for constructing the furnaces4 ,quartz glassware is a highly silicious glass4 ,it is now made and used in the manufacture of special chemical apparatus and laboratory ware such as crucibles1 muffles1 etc41 which have to withstand severe physical and chemical tests4 ,this quartz glass possesses remarkable features in its low coefficient of expansion and resistance to heat changes4 ,it is highly refractory4 ,articles made of this glass can be heated to red heat and plunged directly into cold water several times without fracturing4 ,several varieties of quartz glass are now manufactured1 and a new field for investigation is presented in applying the features and properties of this glass for use in chemical processes4 ,in a purely physical sense glass is a supercooled liquid1 the silicates are only in mutual solution with each other1 and they appear to be constantly changing4 ,glass cannot be described as a homogeneous or definite chemical compound4 ,many of the after effects and changes which occur in glass1 and the formation of crystals in the devitrification of glass tend to prove the above assertion4 ,the colour changes which take place when ruby and opalescent glass is re-heated1 and even the change in colour of glass going through the lehr1 cannot be explained unless in the above sense of viewing these remarkable changes4 ,glasses with an excess of lime in their composition are more subject to devitrification than lead glasses or those of moderate lime content constructed from more complex formulas4 ,the presence of a small proportion of alumina in glass prevents this tendency to devitrification and ensures permanency4 ,those glasses which have the highest silica content1 and which have been produced at the highest temperatures1 show the greatest stability in use4 ,bohemian glasses of this type contain as much as #ge per cent4 silica1 and are produced in gas-fired regenerative or recuperative furnaces1 where the heat approaches #a1ejj ,centigrade4 ,such glass is much sought after for enamelling on1 being harder and less easily softened by the muffle heat firing on the enamels used4 ,taking two corresponding glasses of the same basicity1 or proportion of silicic acid to the bases present1 those formulae which have the greater complexity of bases produce the more fusible glasses4 ,a multiple of bases constituting a more active flux than a single base content1 it follows that a compound mixture of silicates fuses or melts at a lower temperature than the respective simple silicates would4 ,these facts are useful in constructing commercial formulae for glasses4 ,glasses containing lead oxide as an ingredient are subject to reduction when exposed to flames of a carbonaceous nature4 ,the carbon partially reduces the lead oxide to its metallic state1 forming a black deposit4 ,on this account1 lead glasses cannot be used in blow-pipe working with the ease with which soda-lime glasses can be worked1 without reduction taking place4 ,english crystal glass1 which contains a high percentage of lead1 is usually melted in hooded or covered pots to prevent the carbonaceous flames of the furnace reducing the lead and otherwise destroying the clearness of the glassware4 ,soda-lime glass and others without the presence of lead can be melted in open pots without any fear of reduction4 ,modern gas-fired recuperative furnaces1 in which more complete combustion of the carbon takes place1 can now be used for melting lead glasses in open pots1 thus presenting a great saving in the fuel required to melt and produce such glass1 besides permitting the use of a cheaper form of pot4 ,this cannot be done with the ordinary ,english coal-fired furnaces4 ,advantage is taken of the reducing action of the coal-gas flame when producing lustre and iridescent glassware4 ,a small proportion of easily reducible metal1 such as silver or bismuth1 is introduced into the glass and first melted under oxidising conditions4 ,it is then reduced in after-working by flaming1 which deposits the metal in a thin sheen upon the surface of the glass1 where it comes in contact with the reducing flames4 ,an example of this effect is shown in ,tiffany lustre ware1 in which silver chloride is used and reduced within the glass1 giving a pretty coloured iridescence on the surface1 due to the reflection of light from the particles of metal deposited under the surface4 8,aventurine0 is a form of glass in which copper and iron oxides are introduced under reducing conditions during melting4 ,the glass is then allowed to cool slowly4 ,the metallic copper tends to separate out in small spangled crystals1 which give a pretty sparkling effect4 ,the use of strong reducing agents with very slow annealing is necessary to produce this effect4 ,copper and gold ruby-coloured glass presents other instances of partial precipitation of the metal by reduction within the glass4 ,according to the extent of reduction1 the glass ranges in colour from yellow1 ruby1 to brown4 ,the manganese silicate is readily affected by oxidising or reducing conditions1 the purple colour being present under oxidising influences and a greenish-grey colour under reducing conditions4 ,in using manganese as a decolorizer1 the glass maker may have added too much of it to his glass1 in which case it shows too prominent a purple colour4 ,to destroy this excess of colour he pushes either a little strip of green willow wood or a clean potato to the bottom of the pot of metal4 ,the reducing action of the carbonaceous gas involved takes out the excess of purple colour by partially reducing the manganese present to a colourless state4 ,the colour of glass is gradually affected in course of time by sunlight4 ,this change in colour is often noticeable in old windows1 the glass having developed a yellowish green tint in course of time from the action of the solar rays4 ,glass which has been incompletely fused or not sufficiently melted to give a complete solution of the materials present is in a weakened state of cohesion and is liable to disintegration4 ,the presence of undecomposed sulphates1 chlorides1 or borates in the glass also tends to early disintegration4 ,a continual exudation and crystallisation of salt takes place upon the surface until the glass wholly disintegrates away to a white powdered salt4 ,glass is a poor conductor of heat4 ,when a piece of glass has been expanded under the influence of heat1 and is rapidly cooled1 the superficial outer portions become intensely strained and contracted upon the interior portions1 which retain the heat longer4 ,under these conditions of cooling1 glass is apt to 8fly10 or collapse and fall to pieces1 owing to the outer portions giving way under the great strain4 ,these stresses or strains are relieved in the process of annealing1 under which they are gradually eased by a slow and regular cooling from the heated condition4 ,certain glasses1 the composition of which shows considerable differences in the density of the respective bases present1 are more subject to this defect than those in which the bases are of more even density and homogeneous in character4 ,such glasses should be 8de-graded0 and re-melted in order more thoroughly to diffuse and distribute the denser portions throughout the mass4 ,in de-grading glass1 the hot glass is ladled out and quenched in cold water1 dried1 and re-used as 8cullet40 ---------------------------------------- -------------------------------- ,,chapter ,,iv ,,the ,,composition ,,of ,,the ,,different ,,kinds ,,of ,,glass ,the composition of glasses may be simple1 compound1 or complex1 according to the number of bases or acids which may be present in the mixture4 ,the ,simple types of glass are exhibited in the soda silicate1 potash silicate1 and lead silicate4 ,the two former silicates are of most industrial value4 ,soda ,silicate is made from a fusion of #ajj parts of sand with #ej parts of soda carbonate and #e parts of charcoal4 ,the charcoal is added to facilitate the decomposition4 ,the fused mass when cool is transparent and of a pale1 bluish1 sea-green colour4 ,upon boiling it in water it dissolves and gives a thick viscid solution called 8,water ,glass40 ,this is extensively used in the various arts and manufactures4 ,textile fabric and woodwork saturated with this solution and dried are rendered fireproof4 ,in the manufacture of artificial stone it forms1 with lime and other basic oxides1 very stable cements4 ,mixed with silicious or ganister it forms the well-known fire cements for repairing the cracks in retorts1 muffles1 etc4 ,water glass is also used in soap1 and colour making1 and for preserving eggs4 ,potash ,silicate is less used1 being more expensive4 ,it is produced from a fusion of #ajj parts sand1 #fj parts potash carbonate1 and #f parts charcoal4 ,lead ,silicate is composed of #ajj parts sand and #ff parts of red lead fused together4 ,this silicate is mostly used in the manufacture of soft enamels and artificial gems1 and goes under the names of 8,rocaili flux10 8strass metal10 and 8diamond paste40 ,there is another form of soluble glass which is a combination of the soda and potash silicates4 ,this is really a double silicate and may be produced by fusing sand #ajj parts1 soda carbonate #be parts1 potash carbonate #cj parts1 and #f parts of charcoal4 ,this silicate is used in soap making4 ,soluble glass can also be formed by using sulphate of soda as the alkali4 ,in this case1 a larger proportion of the alkaline salt has to be used1 also a larger amount of carbon1 in order to complete the decomposition of the sulphate4 ,a mixture of sand #ajj parts1 saltcake #gj parts1 and carbon #af parts would produce sodium silicate4 ,the boron silicate and borate of alumina are two other forms of soluble glass used in their simple states4 ,the ,compound ,glasses may be flint or crystal glass1 soda-lime glass1 ,bohemian glass1 pressed glass1 and sheet glass4 ,these are the general type of glasses used in the manufacture of domestic glasswares4 ,crystal ,glass1 which is a silicate of lead and potash1 is made from best sand #ajj parts1 red lead #ff parts1 potash carbonate #cc parts1 cullet #ej parts1 to which a small proportion of potash nitre1 arsenic1 and manganese dioxide is added4 ,the bulk of ,english cut-glass table ware and fancy goods are made from this type of glass4 ,it gives very brilliant and colourless results1 more especially when cut and polished4 ,a second-rate quality of crystal glass for table ware may consist of a silicate of lead and soda1 as follows3 sand #ajj parts1 red lead #ff parts1 soda carbonate #be parts1 cullet #ej parts2 with small proportions of ,chili nitre1 arsenic1 and manganese4 ,bohemian ,glass is made from sand #ajj parts1 potash carbonate #ce parts1 lime carbonate #ae parts1 cullet #ej parts2 with small proportions of potash nitre1 arsenic1 and manganese dioxide4 ,this type of glass is used mostly by continental manufacturers for chemical ware1 table and mirror glass4 ,it is a hard1 brilliant1 and stable glass1 very suitable for enamelled glassware4 ,it is a silicate of potash and lime4 ,pressed ,glass consists of sand #ajj parts1 soda carbonate #ej parts1 barium carbonate #ae parts1 cullet #ej parts2 together with soda nitre1 arsenic1 manganese1 and cobalt4 ,this is used by manufacturers of pressed glass table ware or moulded ware4 ,it is a silicate of soda and barium1 the barium having a direct influence in giving a good surface to the pressed goods4 ,crown ,glass consists of a silicate of soda and lime2 sand #ajj parts1 soda carbonate #cf parts1 lime carbonate #bd parts1 soda sulphate #ab parts1 cullet #ej parts2 with traces of manganese and cobalt4 ,this glass is used for making sheet window glass by the crown1 disc1 and cylinder methods4 ,plate ,glass is a silicate of soda and lime2 sand #ajj parts1 soda sulphate #ee parts1 limestone #cj parts1 coal or anthracite #e parts2 with traces of nickel oxide1 cobalt1 or antimony oxide4 ,this is used for cast plate glass1 rolled plate1 cathedral glass1 window and mirror glass4 ,the ,complex ,glasses may be described as those in which more than three bases are introduced1 and constitute such types of glasswares as bottles1 thermometer tubes1 chemical ware1 etc4 ,common ,bottle ,glass may be described as an example of complex formulae4 ,common bottle glass1 or tank metal1 is made from a silicate of soda1 alumina1 lime1 magnesia1 and iron1 as follows3 ,common sand1 containing iron and alumina1 #ajj parts2 greenstone or basalt 7a silicate of alumina1 iron1 lime1 magnesia1 and potash71 #be parts2 dolomite limestone 7magnesia and lime71 #cj parts2 sulphate of soda1 #ce parts2 carbon1 #e parts4 ,felspathic granites may be also used in such glasses4 ,bottle glasses require intense heat to melt1 and are usually dark in colour when made from igneous rocks1 owing to the large amount of colorific oxides present in such materials4 ,these dark colours are not objected to in bottles for stout1 wine1 and beer4 ,it will be noticed these formulae cover a long range1 from the best table glass to the commonest dark bottle glass4 ,besides these1 opal1 opalescent1 and fancy glasses are made1 in which either arsenic1 tin1 alumina1 antimony1 zinc or barium oxides or borates phosphates and fluorides may enter into the compositions4 ,glass makers' recipes vary considerably in the proportions of the various materials used1 according to the locality and the type of furnace used4 ,generally1 it will be found that1 where a gas-fired furnace is in use1 a larger proportion of sand can be used and a cheaper metal produced4 ,the metals produced in covered pots are usually softer and contain more lead and fluxes than those produced in open pots4 ,in using open pots the heat of the furnace has direct access to the surface of the metal therein4 ,in the case of covered pots1 the heat has to be conducted through the cover of the pot1 which retards the heat to a certain extent4 ,on this account1 softer mixtures are used in covered pots4 ---------------------------------------- -------------------------------- ,,chapter ,v ,,coloured ,,glass ,,and ,,artificial ,,gems ,in colouring glass1 either or several of the following colorific oxides may be used4 ,they are added to the batch before fusion4 ,varying proportions are added1 according to the depth of the colour desired4 ,occasionally the colour is influenced by the nature and composition of the rest of the batch4 ,in some instances several colouring oxides are used4 ,in this way many delicate tints are obtained2 in fact1 there are but few colours that cannot be produced in glass4 ,for ,green ,glasses the following oxides may be used3 ,chromium oxide1 #b to #f per cent4 of the batch2 black oxide of copper1 #e to #c per cent42 red iron oxide1 #e to #a per cent42 or a mixture of two or three of the above oxides in less proportions4 ,salts of chromium1 copper1 or iron may be used as the carbonates1 sulphates1 and chromates4 ,for ,blue ,glasses1 cobalt oxide1 #a to #a per cent4 of the batch2 zaffre blue or smalts1 #a to #c per cent42 nickel oxide1 #b to #d per cent42 iron oxide1 #a to #b per cent42 black oxide of copper1 #b per cent4 ,for ,violet and ,purple1 manganese oxide1 #b to #d per cent4 of the batch4 ,for ,rubies1 red oxide of copper1 gold chloride1 purple of cassius1 antimony oxysulphide1 selenium metal in small proportions4 ,for ,yellows1 uranium yellow1 #d to #f per cent4 of the batch2 potassium antimoniate1 #aj per cent42 carbon1 #f per cent42 sulphur1 #e per cent42 ferric oxide1 #b to #d per cent4 ,silver nitrate and cadmium sulphide are also used4 ,black ,glass is obtained from mixtures of cobalt oxide1 nickel oxide1 iron oxide1 platinum and iridium4 ,many very dark or black bottle glasses are obtained by using basalt1 iron ores1 or greenstone in a powdered form1 added to the batch ingredients4 ,white ,glasses or ,opal are obtained by using phosphate of lime1 talc1 cryolite1 alumina1 zinc oxide1 calcium fluoride1 either singly or in double replacements of the bases present in the glass batches4 ,many of the colouring oxides give distinctive colours to glass of different compositions2 also the resulting colours may vary with the same colouring ingredient1 according to reducing or oxidising meltings4 ,thus1 in a batch of reducing composition1 red copper oxide gives ruby glass1 but in oxidising compositions the colour given is green or bluish-green4 ,iron oxide in an oxidising batch gives a yellow4 ,in the reducing batch it gives bluish or green results4 ,manganese is similarly affected4 ,many colouring oxides give more brilliant tints with glasses made from the silicates of potash and lime than if used in glasses composed from silicates of lead and soda4 ,for many colours the lead glasses are preferred4 ,in colouring the batches1 the colouring oxides must be intimately mixed with the batch materials before fusion1 more especially in the preparation of the pale tints1 where only small quantities of colouring are necessary4 ,it is a well-known fact that careful mixings give good meltings1 for then the materials are more evenly distributed and uniformly attacked during the melting4 ,careful and exact weighings are necessary when using colorific oxides1 and a pot is kept for each respective colour melted1 so that the different colours and crystal glasses do not get contaminated with each other4 ,when open pots are used for colours1 the colour pots should be kept together in one section of the furnace1 so that whilst melting1 especially during the boiling up of the batches1 the colours do not splash over into the other pots containing crystal metal4 ,as a rule1 smaller pots are used for coloured glass2 generally they are only a third of the size of crystal melting pots4 ,when this is so1 they are set together under one arch of the furnace1 and the workman informed which pots contain the respective colours4 ,all colour cuttings and scraps should be kept separate from other cullet for re-use4 ,coloured glasses are expensive1 and no waste of glass should be permitted4 ,artificial ,gems4 ,in the manufacture of the glasses for imitation 8paste0 jewels1 every effort is made to procure pure materials and colorific oxides4 ,the base for making artificial gems is a very heavy lead crystal glass termed 8,strass paste10 which gives great brilliancy and refraction4 ,the composition of such a paste would be3 ,best white sand #ajj parts1 pure red oxide of lead #aej parts1 dry potash carbonate #cj parts4 ,these should be thoroughly well melted until clear and free from seed1 and the molten mass ladled out of the pot and quenched in cold water1 or 8de-graded40 ,this assists in making the paste homogeneous4 ,after repeated melting and de-grading1 the paste or cullet is collected1 dried1 and crushed for use in making the coloured pastes4 ,usually1 this strass metal is melted in small1 white porcelain crucible pots holding about #e to #aj kilogrammes of the metal and heated in a properly regulated gas and air injector furnace4 ,the coloured paste is kept in fusion for a whole day1 after which it is slowly cooled and annealed within the pot1 and the gems cut from the lumps of glass thus obtained4 ,the following are some of the compositions used in the preparation of the respective gems4 ,opal4 ,powdered strass paste1 #a1jjj parts2 white calcium phosphate1 #bjj parts2 uranium yellow1 #e parts2 pure manganese oxide1 #c parts2 antimony oxide1 #h parts4 ,ruby4 ,powdered strass paste1 #a1jjj parts2 purple of cassius1 #a part2 white oxide of tin1 #e parts2 antimony oxide1 #aj parts4 ,beryl4 ,powdered strass1 #a1jjj parts2 antimony oxysulphide1 #aj parts2 cobalt oxide1 #be parts4 ,amethyst4 ,powdered strass glass1 #a1jjj parts2 purest manganese oxide1 #h parts2 pure cobalt oxide1 #b parts4 ,emerald4 ,powdered strass glass1 #a1jjj parts2 green chrome oxide1 #a part2 black copper oxide1 #h parts4 ,sapphire4 ,powdered strass glass1 #a1jjj parts2 pure cobalt oxide1 #ae parts4 ,topaz4 ,powdered strass glass1 #a1jjj parts2 antimony oxide1 #ej parts2 uranium yellow1 #aj parts4 ,garnet4 ,powdered strass glass1 #a1jjj parts2 antimony oxysulphide1 #ajj parts2 gold chloride in solution1 #a part2 pure manganese oxide1 #d parts4 ,turquoise4 ,powdered strass glass1 #a1jjj parts2 cobalt oxide1 #e parts2 black copper oxide1 #aj parts2 white opal glass1 made with tin oxide1 #bjj parts4 ,after suitable pieces of glass of the requisite tints are obtained1 they are cut and ground on a ,lapidary's wheel1 then polished1 engraved1 and set as gems4 ,artificial ,pearls are now cleverly made in glass4 ,a tube of the requisite size made of translucent or opal glass is cut into small sections1 which are heated on a tray to softening point whilst set in a rotatory movement4 ,as the heat increases they gradually melt in and seal at the openings1 when they are removed from the tray and sorted4 ---------------------------------------- -------------------------------- ,,chapter ,,vi ,,decolorizers ,decolorizers are the agents employed by the glass maker to neutralise or subdue the objectionable tints given by the colouring action of small traces of iron oxide1 which exists as an impurity present in the materials used or otherwise become accidentally admixed during the process of the manufacture of glassware4 ,the small additions of manganese dioxide1 arsenic1 nitre1 nickel oxide1 selenium1 antimony1 oxide1 etc41 to glass batches may be considered as decolorizers4 ,the most commonly used of these materials is manganese dioxide1 so the action of this material will be explained4 ,every glass maker finds that one or other of the raw materials he uses may contain impurities4 ,it is seldom that glass makers' sand can be obtained that does not contain traces of iron oxide present as an impurity4 ,again1 the cullet collected from the glass house often contains iron scale or rust from the blowing-irons1 which firmly adheres to the glass and gets admixed with the batch for re-melting4 ,the presence of even very small traces of iron in glass becomes evident as a pale sea-green tint when viewed through any thickness of metal4 ,the chemical action of the glass upon the walls of the pot is continually dissolving a minute quantity of iron from the and diffusing it throughout the metal1 giving it a tendency to the pale-green tint4 ,to subdue or neutralise this objectionable tint in the glass1 the glass maker uses certain metallic oxides which give delicate counter-tints4 ,only those glasses which are made from the purest materials can be decolorized to become sufficiently clear to use in making the best table glassware4 ,in optical glassware1 where the use of manganese is not permissible1 the greatest care has to be taken in the selection and testing of the materials to be used4 ,if manganese oxide be used in making optical glass1 although the eye may not be sensitive enough to observe the actual color absorption1 glass is produced in which the solar rays are obstructed1 and much less light is transmitted by the glass when used as an optical lens or prism4 ,therefore the optician avails himself of those glasses which have not been decolorized as being more satisfactory for his purpose1 as more light is transmitted by such glasses4 ,apart from the pale sea-green tint given to glass by the presence of small traces of iron1 certain of the silicates themselves produce natural colors4 ,the soda silicate present in soda-lime metal tends to give a pale bluish-green tint when viewed through any thickness of glass4 ,the lead silicate has a yellowish hue4 ,each of these influences has to be counteracted if clear crystal glass is desired4 ,the decolorization of glass by manganese dioxide depends upon the purple tint it gives to glass4 ,this purple color1 being complementary to the pale green color given by the presence of iron1 serves and acts as a counter-tint1 and by the absorption of the green light1 a less perceptible coloring is produced4 ,in the case of the decolorization of glass1 we get the red and blue of the purple subduing the blue and yellow or green tint given by the iron4 ,but certain other factors are necessary4 ,the purple color from manganese oxide is given only to glass in the presence of oxidizing agents2 and the absence of sufficient oxidising agents in the glass batch1 the purple manganese colour is unstable and its action as a counter-tint is lost4 ,therefore1 the glass maker uses strong oxidising agents in his glass mixtures for crystal effects1 usually in the form of potassium nitrate and red lead1 which liberate oxygen4 ,whilst undergoing decomposition in the glass melt1 the presence of this free oxygen keeps the manganese used in a higher state of oxidation1 and gives the necessary purple coloration4 ,it is also evident that1 if the glass melting in the pot is kept at a high temperature for any considerable length of time1 this period of oxidation cannot last1 and1 after all the free oxygen gas has been evolved1 any further heating tends to turn the glass greenish again or of poor colour1 by the conversion of the manganese into the lower state of oxidation in which the purple colour is not evident4 ,if by chance the glass maker has added too much manganese to the glass1 and the purple colour becomes too evident1 he resorts to the use of a small amount of carbonaceous reducing agent1 such as a piece of charred wood or potato1 which he plunges or pushes to the bottom of the pot by means of a forked iron rod or pole1 where it vaporises1 giving off moisture and carbonaceous gases which reduce the manganese purple colour to a lower oxidised colourless state1 and in a very short time the excess of purple colour has disappeared and the glass appears colourless4 ,much of the success of crystal glassmaking depends upon the proper adjustment of the decolorizers used and obtaining the best colourless effect4 ,the quality of the manganese is important2 only pure manganese dioxide should be used4 ,in many cases the mineral ore1 pyrolusite1 is used on account of its cheapness4 ,this is objectionable1 as much iron may be present in the ore1 when its use as a remedy is worse than the defect4 ,the necessity of taking advantage of the services of a consultant chemist here becomes apparent1 for1 if glass manufacturers would only have their different consignments of materials examined and tested from time to time1 many of the disappointments and difficulties experienced by them at present would be obviated4 ,a considerable saving in the cost of batch materials can be made by the judicious selection of more suitable qualities in preference to inferior or adulterated varieties4 ,in many cases1 a chemist can substitute for certain of the expensive batch materials other cheaper materials introducing the same elements at less expense1 and still retain the same quality in the glass produced4 ---------------------------------------- -------------------------------- ,,chapter ,,vii ,,the ,,refractory ,,materials ,,used ,of the greatest importance to the glass manufacturer are the refractory materials upon which the life of his furnace and pots depends4 ,a few notes giving a description of them and dealing with the manufacture of the fire-resisting blocks used in building the furnaces will be of interest4 ,the chief and most generally used of such materials are the goods4 ,the best known deposits of fire-clays in this country are those in the ,midlands1 ,stourbridge1 ,leeds1 and ,glasgow districts4 ,in each of these districts the mining of fire-clays and the manufacture of fire-resisting goods for furnace work forms an important industry4 ,the theoretical composition of a true would be a double silicate of alumina1 and in this pure state it would be of a very refractory nature4 ,but1 naturally1 fire-clays show the presence of other bases1 such as iron1 lime1 magnesia1 titanium1 and alkalies1 which1 if present to any appreciable extent1 lower the degree of resistance to heat or refractoriness of the clay4 ,these other bases may be considered as impurities or natural fluxing agents4 ,the characteristics of a highly refractory clay suitable for glass manufacturers' requirements would be3 7a7 that such a clay should show no signs of softening at the highest heat of the furnace2 7b7 a squatting point not below ,cone #ca or #afij ,centigrade2 7c7 a high alumina content not below #cj per cent42 7d7 the greatest freedom from impurities2 7e7 a fine-grained texture2 and 7f7 a high degree of plasticity4 ,these are the qualities most essential for glass house work4 ,the figures given by the chemical analyses of good fire-clays would probably fall within the following limits-- ,silica #di to #fe ,alumina #dh to #ca ,ferric ,oxide #je to #ae ,titanium ,oxide nil to #ae ,lime nil to #je ,magnesia nil to #b ,total ,potash and #je to ,soda #ah ,clays of higher silica content than #gj per cent4 would not be considered suitable as pot-clays owing to the case in which glass attacks silicious clays4 ,it is important that chemical analyses of fire-clays should be compared with results obtained from the analysis of fired or burnt samples1 or they should be recalculated to allow of such comparison1 so as to exclude the figures for the hygroscopic and chemically combined water of the clays4 ,the writer gives the following particulars of a very suitable for glass house pot-making4 ,it is plastic and highly refractory1 and is now being considerably used by the trade4 ,the clay is supplied by ,mansfield ,bros41 ,church ,gresley4 ,the figures are from a report made by ,mr4 ,j4 ,w4 ,mellor1 ,d4,sc41 of the ,county ,laboratory1 ,stoke-on-,trent1 and are as follows-- ,raw ,fire-clay ,dried at #aji ,cent4 ,silica #dfde per cent4 ,titanic ,oxide #bfe per cent4 ,alumina #cecb per cent4 ,ferric ,oxide #aca per cent4 ,manganese ,oxide -- ,magnesia #jji per cent4 ,lime #jda per cent4 ,potash #ajh per cent4 ,soda #gf per cent4 ,loss when #abad per calcined over cent4 #aji ,cent ,the melting point is given as equal to ,seger ,cone #cc or #agcj ,centigrade4 ,the physical properties of fire-clays vary as well as their chemical properties4 ,the analysis alone of a is not always sufficient indication as to its ultimate behavior when in use4 ,many physical tests have to be carried out before a clay can be proved satisfactory for a particular purpose1 and much information can be gained by engaging the services of a specialist upon refractory materials to carry out petrographic1 pyrochemical1 and physical tests1 and report upon the suitability of the material for its specific purpose4 ,fire-clays should be plastic1 and this plasticity should be developed to its utmost to increase the binding properties of the clay when used4 ,to develop the plasticity1 fire-clays should be weathered or exposed in thin layers to the action of atmospheric influences4 ,the heat of the sun and the action of frosts and rain have a direct influence in breaking up the clay and developing its better properties4 ,the use of new unweathered clay is the cause of much trouble to the glass manufacturer who makes his own pots and furnace goods1 and on this account he should insist upon having his clays weathered for some time before use1 so as to have them thoroughly matured4 ,before fire-clays are weathered or used for important work they should undergo a process of selection and cleaning4 ,when first raised from the mines all foreign and inferior portions1 carbonaceous matter1 vegetation1 iron pyrites1 and stones are removed4 ,the best and cleanest portions of the are sorted out and removed to the weathering beds1 where the lumps are broken down to small pieces about the size of an egg1 and left to mature and season by weathering4 ,this is then spread out in a layer about #b ft4 deep1 and1 after a period of exposure to the action of the weather1 the heap is turned by men shoveling the clay from one side to the other4 ,the clay1 under the continued action of the wind1 frost1 and rain1 disintegrates and slacks down until it is reduced to a mild1 fine-grained mass1 which condition shows it to be well seasoned and ready for use4 ,fire-clays vary in this respect3 some clays season quickly in the course of a few months1 others take years to develop their proper nature4 ,the former may be classed as mild fire-clays1 the latter as strong fire-clays4 ,after weathering1 the clay is carted or conveyed to the clay-grinding plant1 where it is stored under cover until it is dry enough to be ground on the clay-mill4 ,here the clay is fed into a revolving pan1 and crushed under heavy iron runners1 and1 after passing through perforations in the bottom of the pan1 it is elevated on to screens which sieve the clay to a requisite degree of fineness4 ,it is then admixed with a large proportion of ground-burnt and the mixture is tempered with water until it forms a plastic mass of dough1 which is conveyed to the workshops where the furnace blocks or pots are to be made4 ,these making and drying shops have false or double floors1 under which steam or heated air is passed using pipes or flues below the floors1 giving the steady and uniform heat which is necessary to dry the goods as they are made4 ,heavy goods should on no account be hurried in drying1 lest trouble should occur through the goods cracking or warping4 ,in making the blocks for the furnaces the workman takes a portion of the prepared clay and tramps the plastic mass into a wooden frame1 or mold1 the shape and size of the block required1 with due allowance made for shrinkage4 ,the blocks are made on the warm floor1 which is of cement or overlaid with quarries4 ,when the mold is filled the surplus clay is cut off and the wooden frame is lifted up1 leaving the clay block on the floor4 ,the empty mold is then cleaned and refilled4 ,the blocks are left until they attain considerable stiffness from the evaporation of the water present by the heat of the room4 ,they are then dressed and cut to the final shape desired1 after which they are further dried until they become quite hard and white4 ,when thoroughly dry the blocks are removed from the drying sheds to the kiln for burning4 ,in burning thick and heavy blocks much care and vigilance is required in expelling the chemically combined water present in the clay1 and1 as the temperature rises and approaches red heat1 the rate of heating should be retarded to allow proper oxidation to take place throughout the structure of the blocks1 and prevent black cores from being formed4 ,in all fire-clays1 besides the mechanically admixed water used in preparing the clay to a plastic mass1 which is mostly driven off whilst in the drying shed1 there exists water in a chemically combined state4 ,this the combined water is not expelled below #bej ,centigrade1 and is tenaciously held by many varieties of mild fire-clays4 ,due care has to be exercised in dehydrating goods made from such clays2 therefore the man in charge of the burning regulates his fires1 keeping the kiln at a moderate heat for some time to allow this chemically combined water to be properly and completely expelled4 ,this dehydration stage in burning clay goods occurs between the temperatures of #cjj and #fej ,centigrade4 ,after the dehydration stage of burning is completed1 the fireman raises the temperature within the kiln to a dull red heat1 when the next stage in the process of burning begins4 ,this is the oxidation period1 during which any organic carbonaceous matter present in the clay is expelled4 ,during this stage in burning1 goods require extended time1 to allow for the heated air to permeate and get to the interior portions of the blocks and oxidize the cores2 otherwise the blocks are badly burnt4 ,after the oxidation stage is completed1 the fireman raises the heat quickly until he obtains a high temperature1 sufficient to eliminate and complete the shrinkage of the goods4 ,when this heat is sufficient to complete the fire-shrinkage1 the kiln is finished and is allowed to cool down4 ,the blocks1 when cold1 are then withdrawn and delivered to the furnace builder4 ,for the erection of the furnaces several grades of blocks are used1 according to the conditions and nature of the heat they have to resist4 ,in the presence of reducing agents1 fuel ash1 or glass1 goods vary greatly as to their suitability4 ,so the local conditions to which they are to be subjected whilst under heat should be first ascertained1 and the mixtures for the blocks adapted accordingly4 ,so many differences exist in the pyrochemical and physical properties of clays that their misuse is often apt to occur if the conditions under which they are to be used are not properly understood and allowed for4 ,a may show a the high degree of refractoriness under a fusion test1 and yet be less suitable for a specific purpose than one of less refractoriness showing better physical properties and of the more suitable chemical constitution4 ,the size of grain in both the burnt clay and raw clay used in the mixtures for making glasshouse furnace blocks is of the greatest importance4 ,in many cases it is necessary to grade the ground-burnt material used1 so that the proportion of coarse grains to the fine flour can be regulated to suit requirements4 ,the burnt clay used in making the furnace blocks should be hard and well burnt1 to prevent any after-shrinkage of the goods when they are used in the furnace4 ,fire-clay goods for glass house furnaces should not be burnt at a lower temperature than ,cone #ab1 and in the construction of gas-fired furnaces and tanks1 burning the blocks at a higher temperature1 ,cone #ad would give much better results4 ,on the ,continent the glass manufacturers usually grind and mix their fire-clays1 with the result that they know exactly what they are using in making their pots and furnace goods1 and they are not then dependent upon outside firms to carry out their wishes4 ,english glass manufacturers usually buy their clays ready mixed1 and as often as not have perforce to take the mixtures offered by the clay firms4 ,unfortunately1 in ,great ,britain many of the firms who supply the refractory requirements of the glass trade are exceptionally backward in applying technical knowledge to their trade2 consequently1 progress is somewhat retarded in the glass trade as far as the refractory materials are concerned4 ,so obstinate is this ignorance of science that quite recently one well-known firm replied to an inquiry for samples of fire-clays to be sent for important research work then being undertaken upon the resources of the country1 stating 8that1 as their clay product was perfect1 and research work was quite unnecessary40 ,it often turns out that their conservatism is simply a cloak to hide ignorance1 as it is quite evident to any technicist that there is ample scope for improvement in the present goods on the market1 and such an open opportunity for a scientific investigation into the nature of their fire-clays1 however well known they may be1 should be welcomed with delight1 and every facility and assistance offered for research chemists to improve their material1 and apply tests with the object of developing the best properties of such refractories for special purposes4 ---------------------------------------- -------------------------------- ,,chapter ,,viii ,,glass ,,house ,,furnaces ,the pots within which the raw materials are melted are set within a strongly heated chamber called the glass furnace4 ,the old circular type of ,english furnace usually contains either six1 ten1 or twelve pots1 and will be described first4 ,the pots stand in a circle upon a form of hob called the 8siege10 which constitutes the floor of the furnace4 ,in the centre of this chamber and below the level of the siege is the 8eye0 of the furnace through which the flames come from the furnace fire below4 ,the burning fuel is contained in a circular or cylindrical-shaped fire-box1 about #d ft4 deep and #e ft4 in diameter1 and is supported by a number of strong iron bars across the bottom of the fire-box4 ,passing under the fire-box1 and across the whole width of the glass furnace1 there is an underground tunnel called the 8cave10 each end of which is exposed to the outside air1 which is drawn in through the caves by the draught of the chimney cone above the fires4 ,these caves are of sufficient height and width to allow the fireman1 or 8tizeur10 as he is called1 to attend to the stirring of the furnace fires from time to time4 ,using a long hooked bar of iron1 he rakes out the dead ashes and clinkers1 as they are formed1 and stirs the fire through the bars by prodding the fuel with a long poker4 ,the coal is fed upon the furnace fire through a narrow mouth situated in the glass house leading into a chute which runs under the siege1 from the glass house floor level towards the fire-box of the furnace4 ,the fuel is pushed down this chute and falls into the fire-box and is fed at intervals of the half to three-quarters of an hour1 according to the heat desired and the draught allowed4 ,illustration3 ,,interior ,,of ,,english ,,type ,,of ,,glass-,,melting ,,furnace ,above the siege and over the pots is a covering called the crown of the furnace1 which is supported by fire-brick pillars4 ,this is built of the most refractory material possible to be obtained1 as the hottest flames from the furnace fires beat against this crown and are reverberated downwards upon the surrounding pots4 ,the flames1 continuing their course1 pass between the pots into small openings or flues leading from the siege floor and passing upwards through the pillars which are situated between each pair of pots1 they then escape from little chimneys leading into the outer dome or conical-shaped structure so familiar to outsiders4 ,this outer truncated cone-shaped structure constitutes the main chimney of the furnace4 ,the furnace chamber containing the pots is constructed entirely within this cone4 ,the blocks are carefully shaped1 neatly fitted1 and cemented together with a mortar made of fine1 plastic1 raw ground mixed to thin paste with water4 ,the presence of any molten glass which escapes from a cracked pot1 and the fluxing action of the fuel ashes1 cause severe corrosion of the blocks forming the siege and fire-box1 and these necessarily have to be made of extra thickness in order to extend the life of the furnace4 ,when the furnace crown or siege becomes badly corroded away1 the furnace has to be put out for repair2 so generally an auxiliary furnace is kept at hand1 in order that it may be started and the workmen transferred from one furnace to the other whilst the repairs are being done4 ,illustration3 ,,exterior ,,view ,,of ,,english ,,glass-,,melting ,,furnace ,pot ,trolley in foreground ,the action of the glass upon the siege of the furnace is very active1 and any leakage quickly destroys the blocks1 leaving fissures which gradually increase in size until the blocks are eaten right through4 ,consequently1 every care is taken to preserve the pots from losing metal4 ,if by chance any pot develops a crack through which the metal leaks into the furnace1 the glass working is ceased at that particular pot1 and every endeavour is made to ladle out what remains of the metal1 and so prevent any more running on to the siege and causing further mischief4 ,the metal is ladled out of the pot by means of thick1 heavy1 iron spoons1 with which the hot metal is scooped out of the pot and dropped into a large cauldron containing water4 ,this is very exhausting work1 but there is worse trouble still if the metal is allowed to continue to run through the crack in the pot and over the siege into the eye of the furnace1 for it then fluxes with the ashes of the fuel1 causing them to form into a big mass of conglomerate1 which1 lying in the fire1 interferes with the draught and combustion of the fuel within the furnace1 and before the furnace can be got to work properly again has to be cut away1 piece by piece1 through the firebars whilst hot1 until it is all removed4 ,at the sign of any glass running down into the fires and through the bars1 the tizeur hurries up to give the word that a pot is leaking in the furnace1 and when the pot is isolated the work of ladling the hot metal out into water begins in earnest4 ,a pot which has cracked and leaks is useless for any further work of melting glass1 and at a convenient time it has to be withdrawn from the furnace and a new pot must be substituted4 ,glass-melting pots form a very expensive item in the glass manufacturer's costs2 consequently1 every care is taken to prevent the pots within the furnace from getting chilled by inadvertently allowing the fires to burn too low or allowing cold air to rush through the bars1 through unskilful clinkering and inattention to the furnace fires4 ,sometimes these furnaces are fitted with a ,frisbie ,feeder4 ,this is a mechanical firing arrangement fitted underneath the furnace bars1 by which the fuel is fed upwards into the furnace box1 so that all smoke given off by the fuel baitings has to travel through the hot fuel above1 and thereby is more completely consumed1 giving better combustion than when the black fuel is thrown on the top of the hot bed of fuel4 ,a mechanically operated piston pushes up small charges of fuel from within a cylindrical-shaped box1 which works on a swivel backwards and forwards as the fuel is fed into it4 ,in the old type of ,english furnace containing twelve pots1 each #ch in4 diameter and holding about #ae cwts4 of metal1 the furnace would be capable of melting #g to #h tons of glass a week1 taking #dj tons of best fuel4 ,the more up-to-date glass-melting furnaces are constructed upon a much better principle than the coal-fired old ,english type of furnace just described4 ,these are usually producer gas-fired and give more economy and greater convenience in every way4 ,illustration3 ,,fig4 ,a ,,siemens ,,siegbert ,,type ,,of ,,regenerative ,,glass-,,melting ,,furnace ,in these better types of modern furnaces some form of regeneration or recuperation of the waste heat is usually adopted4 ,these furnaces are much smaller and more compact2 being gas-fired1 they give much higher temperatures1 more complete combustion of the fuel1 greater ease in regulation1 cleaner conditions1 and far greater production than the older types of ,english furnaces4 ,considering the reasonable initial cost that the latest types of these modern furnaces can be built for1 it appears incredible that so many of the old out-of-date ,english furnaces remain in use in this country4 ,illustration3 ,,fig4 ,b ,,siemens ,,siegbert ,,type ,,of ,,regenerative ,,glass-,,melting ,,furnace ,as examples of the types of regenerative and recuperative furnaces1 a description will be given of the ,siemens ,siegbert ,gas-fired ,regenerative ,furnace and the ,hermansen ,recuperative ,furnace for glass-melting1 which are extensively used on the ,continent and are giving remarkably good results4 ,illustration3 ,,fig4 ,c ,,siemens ,,siegbert ,,type ,,of ,,regenerative ,,glass-,,melting ,,furnace ,in the ,siemens ,siegbert type1 the furnace may be a rectangular or an oval-shaped chamber1 approximately #ah ft4 by #i ft41 the crown of which is about #d ft4 #f in4 high4 ,no outer cone-shaped dome exists1 and the pots within the chamber are arranged much closer together and practically touching each other round the furnace4 ,the furnace chamber is heated by a mixture of producer gas and heated air1 the gas being generated in an independent gas producer situated outside the glass house and some little distance away from the furnace4 ,at either end of the furnace1 beneath the floor of the siege1 are two blocks of regenerators4 ,these are deep rectangular chambers containing an open lateral arrangement of fire-brick chequers1 through which the air or products of combustion pass on their way to or from the furnace4 ,port-holes are situated directly above these regenerators which lead the gases through the floor or siege into the furnace chamber4 ,the draught is induced by a tall stack1 which draws the gas from the gas producers through a duplicate arrangement of flues to the port-holes at one end of the furnace1 where it is mixed with the air which has been drawn and heated in its passage through the regenerator beneath4 ,this gaseous mixture1 whilst in combustion1 is drawn across the furnace chamber to the other end of the furnace4 ,the flames playing across the tops of the pots on either side pass down through the port-holes and regenerator at the opposite end4 ,the hot gases or products of combustion1 in passing through the lateral channels of this regenerator1 leave behind their heat by the absorptive or conductive capacity of the fire-brick chequers through which the hot gases have passed on their way to the stack4 ,the direction of the current is reversed at intervals of half an hour or less by using an arrangement of valves situated in the gas and air flues1 so that the currents are made to travel on the contrary direction1 the air necessary for combustion then being drawn through the hot block of regenerators which was previously heated by the exit gases4 ,on its way through these lateral channels the air becomes intensely heated1 and1 when it is admixed with the coal gas at the porthole1 this pre-heated air accelerates the combustion and calorific intensity of the gaseous mixture4 ,the direction of the current is continually being reversed at the interval of half an hour or less by the manipulation of the valves1 so long as the high temperature is desired4 ,in practice1 however1 the regenerators are only used whilst the batch materials are being melted during the night1 and by morning1 when the metal is melted and 8plain10 the heat is brought back1 or retarded1 by using the gas from the gas producers and cool atmospheric air under natural draught1 instead of the regenerated hot air4 ,this cooler mixture1 naturally not being so active in combustion1 maintains just sufficient temperature for working the metal out during the day4 ,later in the day1 when the pots are emptied and refilled with batch1 the regenerators are re-connected and the founding proceeds again through the night1 and the metal is again got ready for the workmen coming in next morning4 ,it will be seen that this method of melting and working out the metal does away with night work1 the furnace man alone remaining in charge during the night4 ,all firing is done outside the glass furnace room1 which is well lighted1 clean1 and free from coal dust1 totally different conditions from those existing in many ,english glass houses of to-day4 ,a ,siemens ,siegbert furnace taking ten open crucible pots1 and filled each day1 turns out #ae to #ah tons of metal a week4 ,the crucibles are about #cj in4 in diameter and have a capacity of #e-a_/b cwts4 of metal each4 ,the amount of fuel consumed is about #ah tons a week4 ,this type of furnace costs about #a1fjj to #b1jjj to build4 ,in the miter's opinion1 a disadvantage of this furnace is that1 during the reversing in the direction of the fire gases1 the greatest heat is suddenly brought to bear on the cooler pots1 resulting in a short life for the pots4 ,the temperature of the incoming air is not so constant as with the recuperative type of furnace2 however1 with proper control1 these defects may be obviated to some extent4 ,illustration3 ,a ,,modern ,,glass ,,house ,the ,hermansen ,continuous ,recuperative ,glass-melting ,furnace in foreground 7,twelve ,covered ,pot ,type74 ,by the kindness of ,messrs4 ,hermansen1 the patentees1 ,i am permitted to illustrate their ,recuperative ,glass-melting ,furnace1 eight pot type4 ,illustration3 ,,hermansen ,,glass ,,house ,,furnace 7,,eight ,,pot ,,type7 ,illustration3 ,sectional ,elevation4 ,a ,,hermansen',s ,,continuous ,,recuperative ,,glass-,,melting ,,furnace ,p4 ,producer4 ,b4 ,burner4 ,g4,p4 ,glass ,pocket4 ,illustration3 ,b ,,hermansen ,,furnace ,cross ,section through ,gas ,producer4 ,p4 ,gas ,producer4 ,r4 ,recuperators4 ,the ,hermansen furnace1 like the ,siemens furnace1 is producer gas-fired4 ,the gas producer is built within the body of the furnace1 7,p7 below the glass house floor4 ,on either side of this gas producer the recuperators are situated4 ,these are constructed by an arrangement of tubes1 designed to give two distinct continuous channels1 the one horizontal and the other vertical4 ,the vertical channels are connected with the atmosphere and supply the air necessary for combustion4 ,the horizontal channels 7,r7 are the flues through which the hot waste products of combustion are continually being drawn from the furnace by the stack4 ,it will be evident that1 the horizontal channels being intermediate to the vertical tubes1 the waste heat is continually being absorbed by the air travelling inwards4 ,in other words1 the air is pre-heated by passing through flues which are surrounded by the hot waste gases4 ,therefore1 in this type of furnace there is no necessity for reversing the currents to procure the necessary pre-heated air for combustion1 and the regulation of the furnace heat becomes a simple matter of controlling the draught by means of the dampers provided in the main flue4 ,in this type of furnace the glass is melted nightly2 open or covered pots may be used1 the capacity of which varies between #e and #ab cwts41 according to the class of glassware manufactured4 ,the furnace is designed in four1 six1 and eight pot types1 and several are now working in this country4 ,these ,hermansen furnaces are capable of producing #bj tons of metal1 with a fuel consumption of #af tons4 ,illustration3 ,c ,,plan ,,of ,,hermansen',s ,,furnace 7,eight ,pot ,type7 ,the ,hermansen ,continuous ,recuperative ,furnace is the most efficient furnace known to the writer4 ,it is easier to control than the regenerative types4 ,being compact1 it takes up little space and is easy to repair1 and its life well surpasses other types4 ,the initial outlay and cost of erection varies from #hej to #a1bjj4 ,the combustion in this type of furnace is so perfect that it is used with open crucible pots for melting lead crystal glasses4 ,on the ,continent this furnace is in general use for all types of glassware1 and1 from the amount of glass it will melt1 its efficiency is greater than the regenerative type4 ,tank ,furnaces are at present used for the melting of the commoner and cheaper types of glass4 ,they are so constructed as to contain a single rectangular-shaped compartment1 or tank1 about #ah in4 to #b ft4 deep1 and from #cj to #ajj ft4 long4 ,the bed and retaining walls of this tank are constructed of specially selected fireclay blocks2 no pots are used4 ,tank furnaces are simple and melt the glass economically1 but the metal produced is not nearly so good a quality as pot metal4 ,tank furnaces are chiefly used for making the cheaper glasswares1 such as wine1 stout1 and beer bottles1 gum bottles1 ink-pots1 sauce bottles1 and like goods1 where a large production is essential4 ,improvements are continually taking place in the design of this type of furnace1 and much finer and clearer metals are being produced4 ,it is quite probable that in the future tanks will be preferred for making cast plate and sheet window glass1 as a larger body of metal is held by them when compared with pot furnaces4 ,like the ,siemens and ,hermansen furnaces1 they are gas-fired1 but the port-holes by which the gas and air are introduced and the products of combustion are withdrawn from the melting chamber1 are situated on either side1 above the level of the metal1 whilst the glass blowers work at one end of the furnace4 ,the melting and working of the metal is continuous4 ,the tank is divided by a shallow bridge1 which is partially submerged and situated midway between the two ends of the furnace1 dividing it into two sections1 respectively the melting and working compartments4 ,this bridge keeps back all unmolten material and allows only that portion which is melted to travel forward to the working compartment4 ,the tank is crowned or arched over1 and at the working end openings are provided to enable the glass workers to gather the metal from within4 ,small rings1 or syphons1 are used1 which1 floating on the metal1 serves further to refine the glass as it is gradually used4 ,the batch mixture is filled through a convenient opening near to the port-holes4 ,tank furnaces vary in capacity4 ,some have been constructed to give an output of #cjj tons of glass a week4 ,this pace can only be kept up with the aid of automatic bottle-making machinery2 in which case hand labor is practically eliminated4 ,liquid fuel or oil-fired glass furnaces have not proved a success1 being very costly in repairs on account of the local heating effects of the flames issuing from the burners vaporizing the oil4 ,electric furnaces for glass-melting have been tried with partial success4 ,these are expensive in maintenance compared with their efficiency in producing glass4 ---------------------------------------- -------------------------------- ,,chapter ,,ix ,,glass-,,melting ,,pots ,,and ,,their ,,manufacture ,glass house pots are large hollow vessels made of refractory in which the glass manufacturer melts the materials of which his glass is composed1 and which retain the molten metal whilst in a state of fusion for the workmen's use4 ,in the case of the lead crystal glass1 the materials1 whilst being melted1 require protection from the flames1 smoke1 and fuel ash present in the old ,english types of furnace chambers1 which would otherwise reduce the lead present to a metallic state and spoil the glass2 therefore1 such glasses are melted in covered or hooded pots and thus protected from the direct action of the flames4 ,consideration has to be given to the extra amount of heat required from the furnace to find its way through the hood of the pot4 ,for crown plate and chemical glassware1 the metal is usually melted in open or uncovered pots4 ,in this case the fusion is facilitated by allowing the heat of the furnace to come into direct contact with the materials within the pots4 ,pots which are covered or hooded have an opening cut out in the front1 in a position just above the level of the molten metal4 ,through this opening the workman gathers the hot metal4 ,in the case of open pots1 the crucible is set in a similar position within the furnace1 but the working hole or mouth is built to form part of the construction of the furnace in front of the crucible4 ,good pots are of the greatest importance to the glass manufacturer1 and upon their life much of the success of glassmaking depends4 ,they have necessarily to resist the corrosive action of the raw materials and molten glass within1 and1 at the same time1 withstand the very intense heat of the furnace without giving way under the great weight of the glass within them4 ,should a pot of metal give way whilst in the furnace1 the loss is considerable and very serious1 for not only has the metal been wasted1 but much of it has flooded the floor of the furnace and siege1 and1 finding its way into the fire-box1 attacks the furnace walls1 fusing and melting with the fuel ash1 checking the draught1 and causing endless trouble4 ,glass house pots are very difficult and expensive to manufacture1 and upon an average each pot has cost #aj by the time it is set within the furnace2 therefore every care is taken to extend their life by procuring the best possible materials for their manufacture4 ,only the best selected pot-clays available are used1 and every endeavour is made to keep them clean and free from foreign contamination4 ,only the best portions of the seam are taken for this purpose1 and a considerable amount of diligence and stringent precaution is taken to procure the best qualities4 ,as the clay is raised from the mine1 clay pickers look over the lumps and select out the best portions4 ,a foreman of long experience is stationed at the head of the mine1 and it is his duty to supervise the clay pickers and see that every care is exercised to guard against any unfortunate results which would naturally attend any indiscriminate or indifferent selection4 ,the best portions having been selected and placed aside1 the lumps are scraped on the surface to remove any dirt1 and broken into pieces about the size of an egg1 which are again carefully examined on all sides and cleaned from foreign matter such as pyrites or bluish parts4 ,if this is carefully done1 and the clays analysed and tested from time to time1 a good pot-clay is obtained4 ,the clay for burning is treated similarly and dried4 ,it is then burnt to a very high temperature and taken to the mill to be ground to the necessary fineness of grain4 ,all pot-clays are well seasoned and weathered before use4 ,they are first ground to a very fine flour and then mixed with a ground-burnt clay1 or 8chamotte40 ,the proportion of raw clay to burnt varies with most manufacturers but depends very much upon the plasticity or binding property of the raw pot-clay used4 ,the burnt clay is preferable if ground to a size about #a to #a-a_/b mm41 being sieved to take out any coarser particles4 ,some clays are more plastic than others1 so the proportions in the pot-clay mixtures may vary from six parts of burnt clay to five of raw1 down to one part of burnt clay to three of raw clay4 ,the proportions are reckoned by volume1 not by weight4 ,the mixture is sieved into a trough and mixed with water to form a stiff paste1 and removed into a large tank1 where it is allowed to soak for some time4 ,it is then well-tempered by treading with the bare feet until the whole mass becomes plastic and tough4 ,the clay mass is turned and trodden several times1 in order thoroughly to consolidate the clay particles4 ,many efforts have been made to do this work mechanically1 but without success4 ,the fact remains1 and experience has proved that1 in the process of treading1 the clay is more consolidated than by any mechanical method of preparation4 ,the tempered and toughened clay is then allowed to sour and mature for a few weeks before use4 ,it is then ready for the pot maker to begin the work of building the pots4 ,the room in which the pots are to be made is kept evenly warm using a series of hot water circulating pipes arranged around the outer walls4 ,usually a temperature of between #fj to #gj ,fahr4 is maintained4 ,double doors are provided at the entrance1 with a porch1 so as to prevent sudden inrushes of cold air and prevent draughts in the pot-making room4 ,all unauthorised persons are prohibited entrance1 and only those who work therein are allowed free access4 ,they are made responsible for keeping the place clean1 as well as looking after the clay and taking care of the pots whilst they are being made4 ,the usual shape of a pot is of round section1 #ch in4 in diameter and #db in4 high1 but many other shapes and sizes are used1 according to the class of goods being manufactured4 ,thus1 for colours1 a very much smaller pot1 less than one-third this size1 is used1 three of them1 taking the position of one large pot1 being set within one arch4 ,for sheet and optical glass1 a covered pot with a very large mouth or working opening is used4 ,in some instances1 as in the ,hermansen furnace1 the pots are oval or egg-shaped4 ,these are used on account of their larger capacity in relation to the space occupied in the furnace4 ,other pots have an interior division1 which has a syphonic refining action upon the glass2 such pots permit of continuous melting and working1 instead of the intermittent process adopted when the regular or common shape is used4 ,for plate glass1 open crucible or bowl-shaped pots are used4 ,in regard to the manner in which the pots are made1 and their subsequent treatment in annealing1 the utmost care and control is necessary4 ,in making the pots1 the pot maker begins by making the pot bottom first1 working the plastic clay paste into rolls about the size of a large sausage4 ,he takes these rolls and applies them one after another in a circular form upon a round level board1 the size of the bottom of the pot4 ,this board is supported on a low table4 ,as he applies each roll1 he presses them together to exclude all air spaces between them1 and continuously work the rolls on the top of each other in circles1 until he gets a circular flat slab of clay in thickness about #d in4 and the width of the pot bottom4 ,he then has the necessary thickness and size of the pot bottom formed as a clay slab1 which is smoothed and leveled over the face with a knife or straight piece of wood4 ,the slab of clay is then reversed upon another board1 covered with a strong hurden cloth and a layer of ground-burnt clay1 which prevents the clay from sticking to the board1 and facilitates drying of the pots4 ,the first board is then removed1 and the pot maker begins to build the sides or walls of the pot upon the circular clay slab by working the clay in rolls around the circumference of the slab to a thickness of #c in41 which gives the thickness of the pot walls4 ,as he works and presses on each roll with his right hand1 he supports the inside of the curve with his left hand1 and presses roll after roll around the circumference of the slab of clay1 increasing the height of the walls until he attains a height of about #f in4 ,the height of this wall is increased by about #f in4 every other day or so2 these time intervals allow each section built to stiffen a little before beginning upon the next section4 ,the workman passes from one pot bottom to another1 building up these sections until he builds each to a height of about #cj in41 when he places within each pot a clay ring about #ah in4 in diameter1 which he has previously made4#c ,after placing these rings within the pots1 the pot maker begins to form the hood or dome of the pot by working on the clay rolls1 and at the same time drawing the sides inwards towards the middle1 lessening the thickness of the walls and gradually diminishing the open space until it is covered and sealed in4 ,whilst the clay is still soft1 the mouth or working opening is worked on and cut out of the dome1 and the whole finished and smoothed by means of wooden tools4 ,footnote #c3 ,these rings1 floating on the metal1 are used by the glass makers to keep back the scum of the glass away from the middle portion from which he gathers4 ,the pots are now completed and are left to dry gradually at a moderate heat1 which is increased a little at the end of a few months in order to thoroughly dry them4 ,they are then removed from the boards and are ready for the furnace4 ,crucible pots are made in a similar way1 except that at the height of about #bg to #cj in4 the pot maker finishes off the top edge of the walls and leaves it in that form to be dried4 ,many efforts have been made to manufacture pots by other methods4 ,one which has been tried with a fair amount of success is to cast the whole pot or portions thereof by using a plaster case mould and pouring in liquid clay slip4 ,another method which has been tried is to press the form by means of a hydraulic press and mould4 ,other mechanical contrivances have been used1 but few of them have given such satisfactory results as the hand-made pots4 ,,mixture ,,for ,,pot-,,clay ,by volume4 7,base7 ,fine ground strong #e parts ,fire-clay 7,binder7 ,fine ground mild ,plastic #d parts ,fire-clay 7,grog7 ,ground burnt ,chamotte #b parts 7,grog7 ,ground selected ,potsherds #a_/b part ,the fusion point of the mixture should not be less than ,cone #cb1 or #agaj ,centigrade4 ,strong fire-clays are those coarser and harder grained1 and are usually more silicious and less plastic than the mild fire-clays4 ,mild fire-clays are very fine-grained1 plastic1 and easily weathered clays4 ,they act as the binder portion in fixing the burnt grog used in pot-clays4 ,the raw clays should be ground very fine and separately from the burnt clays4 ,the ground burnt should be crushed from hard and well-burnt fire-clays1 and should pass a sieve of ten meshes to the linear inch4 ,the mineralogical composition of the fire-clays for making pots is important4 ,the presence of pyrites renders fire-clays unsuitable as pot-clays4 ,some indication as to the subsequent behavior of a can be obtained by submitting it to a petrographic examination1 and the usual pyrochemical and physical tests carried out in testing refractory materials4 ,in this country1 ,stourbridge pot-clays are chiefly used for pot-making1 and so conservative are the majority of glass manufacturers that they will not use other clays1 although1 in the writer's opinion1 many better clays exist in ,great ,britain1 and have now been introduced and used successfully by some firms for pot-making4 ,ground potsherds are selected pieces of old broken pots1 cleaned from any adhering glass4 ,these selected pieces are crushed and ground in a similar way to the burnt clay1 and sieved to the same degree of fineness before use4 ,plumbago glass house pots are sometimes used4 ,these are made from mixtures of graphite1 or plumbago1 and raw 4 ,they are very refractory and withstand the attack of very basic glasses1 where such have to be manufactured4 ,pot rings are made by taking a long roll of clay about #c in4 in thickness and shaping it around a circular frame4 ,the two ends are joined and finished smoothly1 the frame took away1 and the ring dried4 ,a ring is placed in each pot4 ,stoppers are the lids used to close the mouth of covered pots whilst the metal is being melted4 ,these are made in plaster case molds by pressing a bat of clay into the desired shape and releasing the outer case by turning the whole upside down upon a board and lifting off the mold4 ,an indentation is made in the middle1 forming a small hole4 ,an iron rod can there be inserted1 by which the stopper can be lifted away from the pot mouth whilst hot4 ,stoppers are burnt before use and are made in various sizes to fit the mouths of different pots4 ,it is always advisable for the glass manufacturer to make his pots and prepare his clay1 as he then knows exactly what he is using1 and he is not dependent upon outside firms for his pots as he has them ready at hand when needed4 ,the conveyance of pots from one district to another by rail or road is always accompanied by considerable risk1 as the vibrations are given they in such journeys often cause mischief4 ,as they are very heavy and fragile1 their loading and unloading into the wagons is often attended with a mishap4 ,as often as not1 latent strains are caused1 which only develop when the pot is put in the furnace4 ,annealing and ,setting the ,pots in the ,furnace4 ,the pots1 when made and dried1 being of raw clay have to be carefully annealed before they can be introduced into the hot furnace4 ,in doing this1 the pot is removed from the drying rooms and placed within a small auxiliary furnace called a pot arch1 which is constructed purposely to anneal them and get them hot before placing them in the glassmaking furnace4 ,the pot is moved by picking it up on a long three-pronged iron trolley1 made purposely to lift and move them about4 ,the pot is set within the pot arch1 resting upon two or three rows of fire-bricks1 which allows the trolley to be removed and brought away1 leaving the pot in a raised position in the pot arch4 ,the doors of the pot arch are then closed and sealed with a stiff clay paste or mortar1 and slow fires started which gradually heat the pot1 until at the end of a week it is got to a white heat1 and the pot is ready to be removed and set within the furnace for melting the glass4 ,at a convenient time1 arrangements are made for setting the pot4 ,all other work about the glass house has to cease1 as all hands are required to help in the strenuous and arduous work4 ,the old pot in the furnace1 which has done work for several months1 has to be withdrawn from the furnace and the new pot from the pot arch has to take its place4 ,we see gangs of men here and there4 ,some are pulling down the wall of bricks from the front of the old pot1 making an opening in readiness to remove it4 ,another gang of men advance with long1 heavy1 strong iron crowbars1 sharpened at the points1 with which by heavy blows and levering they endeavour to loosen the old pot from the floor of the siege1 to which it has become firmly cemented by the heat and any leakage of glass which may have taken place4 ,eventually1 by their combined exertions1 they succeed in loosening the pot1 and then1 levering it up1 they place the low iron pot trolley under it and drag it out of the furnace1 whence it is taken away and thrown aside4 ,the old pot having been removed from the furnace1 the glowing heat radiates more intensely than ever into the faces of the men at work1 who endure it in relays whilst they work clearing away the old bricks and preparing the siege for the new setting4 ,when this is done1 a gang of men open the pot arch doors1 and1 placing the iron trolley under the new pot1 convey it to the opening in the glass furnace from which the old pot has been removed4 ,facing the terrific heat1 they struggle to push the new pot into its place in the furnace1 with the aid of crowbars1 and working in relays1 in turn face the heat till at last it is got into position4 ,naturally1 everything has to be done in a hurry1 so that the new pot may not be chilled before it is got into the furnace by being exposed too long to the outside air4 ,the whole work proves very exhausting to the men1 as there is little protection from the heat4 ,after the pot is set in its place1 the trolley is brought away and the wall of bricks rebuilt up in front of the pot to protect it1 clay being daubed over the exterior of the brick wall to prevent any inrushes of air1 which would cause the pot to crack by finding a way through the joints in the brickwork4 ,the furnace1 during these operations1 is driven and worked to its full capacity1 so as to allow for the very considerable loss of heat which takes place whilst the opening is being made and the pots removed4 ,the above is a description of the usual method of pot setting4 ,in more modern and up-to-date works a travelling chain screen is used4 ,this screen is like a curtain of loose chains1 which is adjusted to hang in front of the open arch of the furnace and protects the workmen from the fierce heat4 ,at the same time it permits the workmen to see and carry out the work of pot setting with greater ease and convenience4 ,in using this screen arrangement whilst setting1 the pot is pushed through the chain screen1 which closes upon it after it has passed through4 ,the workmen are thus enabled to get closer to their work by manipulating the crowbars through the screen as the heat is not radiated full upon them4 ,the newly set pot is allowed to stand empty in the furnace for a day or two to regain heat before it is filled with batch4 ,it is first glazed on the inside by a workman taking a gathering of glass from another pot and plastering or covering the inside all round with the hot metal1 which flows down and glazes the surface of the pot1 giving it a certain amount of protection from the attack of the raw batch materials which are to be introduced later4 ,the founder1 or glass melter1 now takes charge of the pot1 and he brings up the mixture of batch and cullet and shovels it into the empty pot until it is filled well above the mouth or level of the opening4 ,the heat of the furnace melts the batch1 and after several hours it becomes liquid and shrinks in volume so that probably only two-thirds of the height or capacity of the pot is occupied4 ,the pot is then again filled with more batch materials until it is full of molten metal up to the level of the mouth of the pot4 ,the furnace is kept going at its full heat until the founder1 drawing a small portion of the glass on the end of an iron rod1 examines it and finds that it is melted clear and free from seeds or bubbles of gas4 ,when clear1 the metal is 8plain10 and at this stage is in a very liquid1 fluid1 and watery state1 too liquid to be easily gathered4 ,it is1 therefore1 allowed to cool off by removing the stopper down and leaving the mouth of the pot open1 until the glass becomes more viscid1 or of a stiffer nature4 ,the glass is then skimmed by dragging off any scum present on the surface1 which is due to undecomposed salts that may have risen during the melting4 ,the metal is now ready for the glass blowers to begin work4 ,upon looking into the pot1 the ring will now be noticed floating on the surface of the glass4 ,this ring keeps back from its interior any further scum that may arise whilst work is in progress4 ,the glass blower always gathers from within this ring1 where the metal is cleanest2 and from time to time the metal within the ring is skimmed in order to keep that portion in the best condition4 ,when the greater part of the metal within the pot has been gathered or worked out1 the heat of the furnace is raised again and fresh batch materials filled and the process repeated4 ,the time taken to melt the glass depends upon the heat of the furnace4 ,a gas-fired furnace will melt the batches in eight hours1 but the old type of ,english furnace takes much longer1 usually two to three days4 ---------------------------------------- -------------------------------- ,,chapter ,x ,,lehrs ,,and ,,annealing ,owing to the peculiar structure of glass1 and its liability to fly or collapse when exposed to sudden changes of temperature1 a process of annealing becomes necessary in order to produce a more equal distribution of the tensions throughout the structure of the glass2 otherwise1 glassware of any thickness would be in such a state of tension as to be extremely liable to fracture when passing through any sudden change in the atmospheric temperature1 especially in frosty weather4 ,in this state it is useless or dangerous for general purposes4 ,on this account most glasswares undergo a form of annealing at some time during the process of their manufacture4 ,and in the case of certain goods1 such as table glass1 lamp glasses1 optical glass1 etc41 special care and time are devoted to this process of annealing4 ,often in the case of improperly annealed glass1 instances are known where its unhomogeneous structure has suddenly given way as the result of derangements set up by internal tension4 ,friction1 or rough handling whilst cleaning1 at the ordinary temperature of the atmosphere1 is sufficient to cause a rupture4 ,therefore annealing cannot be too carefully attended to4 ,for annealing the glass manufacturer uses a lehr1 which is an arched tunnel with a fully exposed opening at the exit end and partially closed at the entrance end1 where the goods are introduced4 ,the lehr is heated at the entrance end to a temperature of about #cej ,cent41 which temperature is gradually diminished towards the exit end1 which is quite cool4 ,the hot end1 or entrance1 should be constantly at a temperature just short of the actual deformation or softening point of the glass introduced2 usually the entrance is in a position near1 or convenient to1 the glass furnace around which the glass blowers make the goods4 ,in old-fashioned works coal-fired lehrs are used1 but they are very unsatisfactory and difficult to regulate4 ,the heat of the lehrs in modern works is maintained and regulated by a series of gas burners situated under the floor of the tunnel or lehr4 ,along this floor are placed iron trays linked up with each other to form a continually travelling track1 which gradually moves towards the cold end of the lehr2 these trays are operated by a mechanical jack and gears4 ,as each tray of goods comes out of the cooler end of the lehr1 they are taken off and conveyed to the warehouses for cleaning and packing1 and the empty tray is sent back to the entrance end to be linked up and refilled again with fresh goods4 ,these tunnels1 or lehrs1 are about #dj ft4 long1 and as the glasswares travel through on the trays they are subjected to the gradually diminishing heat1 until they are ultimately removed at the cooler end in an annealed condition1 in which state they are less liable to fracture in use4 ,the time occupied in travelling through the lehr is usually about three days4 ,but this period varies according to the nature of the ware being manufactured4 ,in special glasses1 and in the annealing of optical glass1 the glass may undergo a process of annealing that takes as long as ten days1 and in other cases1 where the glassware is made very thin1 no annealing at all is necessary4 ,usually the thicker and heavier articles require the longest time in annealing4 ,table glass which is made thick and heavy for cutting or decoration requires a little more care and time in the lehr than ordinary plain glassware1 as the abrasive action of cutting quickly develops any latent strains and causes fracture4 ,in some works1 especially on the ,continent1 several small externally-heated kilns are used for annealing1 in which the hot glassware1 as it is made1 is packed in tiers2 when full1 these kilns are closed up and then allowed to cool of their own accord2 after which they are opened and the goods taken out to the warehouse4 ,this is an intermittent process of annealing1 and is quite satisfactory for certain classes of goods1 such as lamp shades1 which are usually of equal thickness throughout their form4 ,the travelling or continuous form of lehr admits goods of more unequal thickness in form and variety4 ,thus1 wine-glasses1 jugs1 and bowls may be annealed together with less risk of malformation in their shape than would be present if they were annealed together in kilns4 ,the manufacturer can1 by suitably arranging the temperature of the gas burners1 give more heat to one side of the lehr than to the other4 ,he then places the heavier goods on the hotter side and reserves the other for lighter goods1 such as wines1 etc4 ,they then travel down together side by side under the most suitable conditions for the annealing of each class4 ,many physical changes take place in the glass passing through the lehr4 ,one remarkable effect is the slight change in colour which occurs in glass decolorized with manganese4 ,it is noticed that the glass becomes a greener tint in passing through the lehr when the decolorization is just on the margin of efficiency4 ,the state in which the structure of glass exists when quickly cooled and the action of annealing might be explained4 ,when glass is quickly cooled1 being a bad conductor of heat1 insufficient time is allowed for the middle or interior portions of the glasswares to settle down and assume their normal state of solidification4 ,the outer portion1 or crust1 will first cool and contract with an enormous strain upon the hot interior4 ,this difference in the state of tension between the outer and interior portions gives a want of uniformity1 and stresses of tension and thrust are developed1 which cause the whole to collapse with the slightest external scratch or heat change4 ,in annealing1 this strained or forced condition in the structure of the glass is relieved by subjecting the glass to a pre-heating1 and gradually diminishing the temperature1 allowing a sufficient time for the different layers mutually to adjust themselves to their comparative normal positions1 and thus relieve the strains within the mass4 ,much depends upon the pre-heating temperature and the rate at which the diminution of the temperature takes place4 ,if this is properly provided for1 the best results are obtained in the stability of the resulting glass4 ,the presence of any stress can be determined by using a polariscope4 ,the average ,british glass manufacturer has little knowledge of the value of a polariscope1 or stress viewer1 in ascertaining the physical state of his glasswares1 and until he adopts its use there is little prospect of an improvement in his annealing methods4 ,much faulty annealed glass is being turned out which the glass manufacturer is not aware of1 and which could be avoided by the intelligent use of such a simple instrument1 which detects badly annealed glass at once by the aid of crossed nicols and a selenite plate4 ,owing to the unequal densities of the various silicates present in the heavy lead and barium glasses1 they are more subject to striation and require more careful annealing than the soda-lime glasses1 in which the silicates present are of more equal density4 ,however1 much depends upon the proper 8founding0 and melting of such glasses4 ,the use of a larger proportion of cullet assists in breaking up striation4 ,the presence of striae or cords in glass disqualifies it for most purposes1 as it is usually found that1 apart from their defective appearance1 they tend to produce stresses within the glass4 ,transparency1 brilliancy1 stability1 and homogeneity are important factors in producing perfect glassware1 and the proper development of these distinguishing properties requires considerable skill on the part of the glass manufacturer1 alike from a technical1 physical1 and practical standpoint4 ---------------------------------------- -------------------------------- ,,chapter ,,xi ,,the ,,manipulation ,,of ,,glass ,,glass ,,makers' ,,tools ,,and ,,machines ,the tools used by the glass blowers are few and simple4 ,the greater part of the crude form is produced by blowing out the hot glass into a spherical or pear-shaped bulb and regulating the size and thickness by gathering more or less material4 ,the tools are mainly employed in finishing and shaping this bulb into the desired form1 such as shearing1 forming the neck spout1 crimpling1 and sticking on the handles to the various shapes made4 ,according to the type of the goods manufactured1 different manipulative methods in forming the articles are adopted in various works4 ,the best ,english table glassware is mostly hand-made blown ware1 generally entirely executed by the handicraft of the workman without the aid of moulds to form any part of the articles1 and a considerable amount of skill and practice is necessary before the workman is competent enough to shape a number of articles exactly to the form of his model4 ,it is astonishing to notice the skill and precision with which a workman produces wine-glasses one after another1 so uniform that one cannot trace any dissimilarity between them4 ,a second class1 or cheaper form1 of tableware is made by blowing the sphere or bulb of hot glass within a mould1 to give some part1 or the whole form1 of the desired article4 ,if only a portion of the intended shape is thus formed by the mould1 it is afterwards finished by hand with tools4 ,this is the general continental method of working1 and has only been partially adopted by this country for making tableware4 ,where a number of articles of one shape have to be produced1 this is by far the most economical method4 ,glass tumblers1 honey pots1 and rose bowls illustrate this class of ware4 ,another class of tableware produced by a method of pressing the form is known as 8,pressed glassware40 ,the hot metal is gathered from the pot and a portion cut off1 and allowed to fall into an iron mould fixed within a lever press1 which carries a plunger fitting within the mould formed to shape the interior and exterior1 with the thickness of the glass as the intermediate space between them4 ,as the hot glass is introduced1 the workman brings down the lever arm and the plunger presses the hot metal to shape4 ,the plunger is then released and the mould reversed1 turning out the pressed form of glass1 which is then carried away to be fire-polished or further manipulated with tools before it goes to the lehr4 ,the case or mould portion is made in two halves1 to facilitate the removal of the hot glass after being pressed4 ,pressed glass tableware can be recognised by the presence of seams1 showing these divisions of the mould4 ,many exquisite designs imitating cut-glass tableware are executed in pressed glassware4 ,the moulds are a very expensive item1 as there is much tool work in cutting the patterns and refacing them after prolonged use4 ,in making pressed goods1 an oily1 carbonaceous liquid is used to give the moulds some protection and prevent the oxidation of the iron4 ,this liquid is from time to time applied1 as the work of pressing proceeds1 by mopping the interior of the mould with a mop dipped in the preparation4 ,another process in glassmaking is that of bottle-making by automatic machinery1 in which the glass worker does little but gather the requisite quantity of glass from the pot and place it into the revolving clips of a bottle-making machine1 which does the work of formation1 by the aid of compressed air delivered from a supply main4 ,this is largely of ,american introduction1 and is the method adopted in making common bottles4 ,in some cases the bottle neck may be finished by a hand tool after a mould has done its part of forming the bottle4 ,modern machines have been perfected to do the whole work of gathering the metal1 forming the shape1 and completing the bottle2 a number of arms travelling round a track carry the mould forms1 which alternately dip into water to keep them cool1 open to receive the hot metal1 close1 deliver a requisite pressure of air to extend the hot glass within the mould1 and then deliver the bottle on to a travelling belt1 which takes them to be annealed4 ,in the manufacture of bottles by machines1 hand labour is practically eliminated as far as the actual making of the bottle is concerned4 ,the bottle-making industry is undergoing great changes by the introduction of such machinery4 ,in some plants a ten-armed machine will produce automatically #abj gross of #af oz4 bottles in twenty-four hours1 at an average cost of #as4 #f;d4 a gross4 ,owen's ,bottle-making ,machines are of this type4 ,such machines produce #gjj bottles an hour1 according to their size and the number of arms fitted to the machine4 ,as an illustration of a less complicated bottle-making machine1 8,the ,harlington0 may be described4 ,this machine consists principally of a table1 on which is arranged on the left-hand side a parrison mould1 and on the right-hand side a column with a revolving table carrying two finishing moulds4 ,illustration3 ,by permission of ,melin ,co4 8,,the ,,harlington0 ,,bottle-,,making ,,machine ,below the table1 near the parrison mould1 is arranged an air cylinder1 through which a piston runs1 operated by a hand lever4 ,on the upper part of the column1 on which revolves the table with the two finishing moulds1 is also arranged an air cylinder operated by a hand lever4 ,the method of working is now as follows-- ,a gatherer puts the metal into the parrison mould into which it is sucked by moving the left-hand lever4 ,through this operation the head of the bottle is formed and finished4 ,by reversing the lever1 air enters the parrison1 thus blowing the same out to the height of the parrison mould4 ,the parrison mould is now opened and the parrison hanging in the head-mould held by the tongues is placed under the blowing cylinder above the open finishing mould4 ,now the latter is closed1 and by moving the lever1 the bottle is blown and finished4 ,whilst this last operation is being effected by a boy1 the table is revolved and the previously finished bottle is taken out and another parrison is made ready to be handled in the described way4 ,this machine produces #bjj bottles per hour4 ,the ,glass ,blower's ,tools4 ,the glass maker's chief tool is the blow-iron4 ,this is a tube of iron #a_/b to #a-a_/d in4 wide and about #d to #e ft4 long1 one end of which is shaped or drawn in so as to be convenient for holding to the lips1 and the other end is slightly thickened into a pear-shaped form1 on which the hot metal is gathered4 ,in making crystal tableware the workman manipulates the glass he has gathered on this blow-iron by marvering it on a marver4 ,this is a heavy slab of iron with a polished face about #a ft4 by #a ft4 #f in41 and #a in4 thick1 supported on a low table4 ,sometimes this marver may be a block of wood with hollows of definite forms1 in which the workman rotates the hot glass he has gathered to regulate the form and thickness of the metal to suit his work before beginning to blow it out into a hollow bulb4 ,the pontil is a solid rod of iron of similar length and thickness to the blow-iron4 ,by gathering a little wad of hot glass on the pontil and sticking it against the end of the bulb attached to the blow-iron1 the workman can detach the bulb from the blow-iron and hold it by the pontil to which it has been transferred1 and which enables him to work on the other end or opening in the bulb which is exposed in detaching it from the blow-iron4 ,illustration3 ,,glass ,,worker',s ,,chair ,after re-heating the glass1 he may shear it with his scissors or shears1 open it out with his pucellas1 crimple it with his tongs1 measure and caliper it1 or shape it to a template4 ,whilst he is doing such operations he sits in a glass worker's chair4 ,this chair has two long extending arms1 which are slightly inclined1 and along which he rolls his blow-iron or pontil1 with the glass article attached1 working upon the rotating form1 turning the iron with one hand1 whilst he uses his tools with the other hand1 to shape or cut the glass to its requisite form whilst it is hot1 soft1 and malleable4 ,the shears are like an ordinary pair of scissors1 and are used for cutting the hot glass1 or shearing off the tops of bowls and wines to their proper height4 ,the pucellas is a steel1 spring-handled tool in the form of tongs1 which the workman uses to widen1 extend1 or reduce the open forms of glass by bringing pressure upon the grips of the tool whilst applying it to the hot glass4 ,the glass maker also uses another form of spring tool in taking hold of hot glass or pinching hot glass to form4 ,these are the tongs4 ,the battledore1 or palette1 is a flat board of wood with a handle1 used for flattening and trueing the bottoms of jugs or decanters1 etc4 ,the chest knife is a flat bar of iron1 usually an old file1 used for knocking off the waste glass remaining on the blow-irons and pontils after use4 ,a chest or iron box is kept for collecting such waste glass for further use4 ,a pair of compasses1 calipers1 and a foot rule complete the glass maker's outfit of tools4 ,making a ,wine-glass4 ,the manipulations in the manufacture of a wine-glass will now be described4 ,a common mule wine-glass is formed from three distinct pieces of glass3 7a7 the bowl2 7b7 the leg2 7c7 the foot4 ,a wine 8shop10 or 8chair10 consists of three men2 a 8workman10 whose main work consists of finishing the wine-glass2 a 8servitor10 who forms or shapes the bulb2 a 8foot maker10 who gathers and marvers the glass2 and a boy who carries away and cleans the blow-irons4 ,the 8footmaker0 of the 8chair0 gathers on the end of a blowing-iron sufficient glass to form a bowl4 ,this is then shaped on a marver until the required shape is obtained4 ,the footmaker then blows this out to a hollow bulb similar in size to the pattern to which he is working4 ,when the bulb leaves the footmaker it is the shape of the bowl of the wine-glass4 ,this is then handed over to the servitor1 who drops a small piece of hot glass on to the end of the bulb1 and heats the whole by holding it in the furnace4 ,this serves to make the joint of the two pieces perfect4 ,the servitor next proceeds to draw out the leg from the small piece of glass at the end of the bulb1 leaving a button of glass at the end of the leg4 ,the servitor then dips the end of the leg into the molten glass within the pot and gathers on sufficient glass to form a foot4 ,he spreads this portion of the glass out to the required shape and size with a pair of wooden clappers1 with which he squeezes the hot glass to form the foot4 ,the servitor has now done his part of the work1 and the glass is handed to the workman4 ,it is then cracked off1 and the foot caught by a spring clip arrangement attached to a pontil1 called a 8gadget40 ,the workman now re-heats or melts the top edge of the glass by holding it within the furnace1 and when it is hot he cuts off the surplus glass with a pair of shears4 ,a line is chalked on at the correct distance from the foot1 and guides the workman in cutting the glass to the proper height4 ,he then melts the top again and opens it out with his spring tool to the required shape1 after which the glass is taken to the annealing lehr by the boy1 to be annealed4 ,other forms of wine-glasses are made1 and various methods are adopted1 according to the district and class of workmen4 ,for instance1 the method of making the above common mule wine-glass varies in different districts4 ,instead of gathering the metal for the foot upon the leg of the glass1 the workman may drop a piece of hot glass1 which has been gathered by the servitor1 on to the button at the end of the leg1 and by means of a pair of wood clappers spread the hot glass to form the foot4 ,in another method of making a wine-glass1 the stem or leg is drawn out from the body of the bulb by pinching down a knob at the end of the glass4 ,the servitor draws the leg out of this knob and knocks off the extreme end4 ,meanwhile1 the footmaker has been preparing a foot1 gathering a small portion of metal on a blow-iron and blowing it out and shaping it into a double globule4 ,the end globule forms the foot and the second merely acts as a support4 ,the footmaker takes these globules1 and the servitor sticks them on to the drawn stem of the wine whilst it is hot2 the blow-iron holding the globules is knocked away1 leaving them adhering to the leg of the wine-glass4 ,the footmaker then knocks off the second globule at the line between the two and1 re-heating the bulb at the foot of the glass1 opens and widens the edges out4 ,the glass then goes to the workman to be finished in the same way as the common mule wine-glass4 ,many articles of glassware are formed with the aid of moulds4 ,take as an illustration the manufacture of tumblers and honey pots4 ,a quantity of glass is gathered on the blow-iron1 marvered1 and blown out into an elongated bulb1 which is introduced into a mould divided in two halves1 which open or shut by hinges1 a handle being fixed on either half to facilitate the operation4 ,the interior of the mould is made to the shape of the article1 and as the bulb of hot glass is introduced it is shut1 and the workman blows down his blow-iron and extends the glass until it expands and fills the space within the mould1 giving the complete form of the article with a surplus of metal just where the blow-iron is attached to the glass at the top4 ,these tops are then cut off and finished1 either by the workman re-heating the article by attaching the bottom to a pontil and shearing off the top edges1 or the glass is annealed in its unfinished state and the top surplus portion cut off by an automatic machine specially constructed for cracking off such goods4 ,illustration3 ,,glassware ,,blown ,,in ,,moulds ,,showing ,,portions ,,cracked ,,off 7a7 ,tumbler4 7b7 ,honey ,pot4 ,such machines consist of a set of revolving tables upon which the glass articles are centred1 and each in turn revolves in front of a thin1 pointed1 hot jet of gas flame1 which impinges on the glass at the height at which the glass is to be cracked off4 ,after one or two revolutions in front of this hot pencil of flame1 it is removed1 and1 by applying a cold steel point so adjusted as to touch the part where the jet has heated the glass1 a chill is imparted which causes the upper portion of the glass to crack away in a clear1 sharp line round the glass4 ,this top portion of surplus glass is thrown aside and returned to the furnace for re-melting as cullet4 ,the tumbler or honey pot is then conveyed to another machine which fire-polishes the edges to a smooth finish4 ,this machine consists of a circular revolving frame carrying small supports1 which themselves rotate on their own centres4 ,upon each support an article is placed to be fire-polished and the frame carries them round1 and they travel into another section of the machine1 passing under a hooded chamber1 which is heated by a fierce jet of flame4 ,the jet of flame1 which is localised on to the top edges of the tumblers or other goods passing through the hood1 gives just sufficient heat to melt and round off the sharp edges of the glassware where they have been cracked off by the previous machines4 ,by using these machines in this way labour is considerably economised1 and as many as #cjj or more articles an hour can be cracked off and fire-polished with unskilled labour4 ,these machines are extensively adopted in the manufacture of electric light bulbs1 shades1 lamp chimneys1 and tumblers4 ,moulds are usually opened1 shut1 and dipped by boys1 but in up-to-date glass works an automatic machine called a 8,mechanical ,boy0 is used4 ,with this machine1 the mould is operated at the desire of the workman and not at the desire of the boy4 ,the output is considerably expedited by the use of these automatic devices for opening and shutting the moulds4 ,it is obvious that whatever the shape of the mould1 or whatever the design within the case1 the glass takes the impression and retains it in after working4 ,in this way1 square sections1 fluted indentations1 or raised bosses can be formed with facility and regularity4 ,illustration3 ,by permission of ,melin ,co4 ,,vertical ,,cracking-,,off ,,machine ,the ,glass ,workers' ,union consider that the introduction of machinery deprives men of their independence and right to work1 but as yet the glass blowers have been always fully occupied with useful work about the factories in which such machines have been introduced1 so it cannot be said that they have been forced to be idle4 ,the advantages possessed by these automatic machines in their larger output at so much less cost compared with hand labour is the great factor in inducing their adoption2 and in these days of progress and competition such machines enable the glass manufacturers to cope with the increasing demand and go far towards bringing a factory up to date and making it well equipped4 ,manufacturers should certainly turn their attention to these mechanical methods1 as their use is quite general on the ,continent and in ,america1 and by their use the metal can be worked out of the pots or tanks much more quickly1 increasing considerably the turnout or capacity of the furnace against the fuel consumption4 ,much of the glassware imported into this country is composed of such articles as would have been manipulated by machines1 and1 unless a similar method of manufacturing them is adopted here1 we cannot hope to compete with other countries in supplying our own needs4 ,in the writer's opinion1 it is mainly due to the adoption of machinery for producing glassware that the continental people have been enabled to undersell us in our own market1 and ,english manufacturers could produce at a much cheaper rate if they would only adopt similar methods of manufacture and the gas-fired furnaces as used abroad4 ---------------------------------------- -------------------------------- ,,chapter ,,xii ,,crown1 ,,sheet1 ,,and ,,plate ,,glass ,the glass used in windows may be either crown1 sheet1 or plate4 ,crown ,glass is made in the form of circular flat discs about #d ft4 in diameter4 ,the workman1 by repeated gatherings1 collects sufficient glass on the end of his blow-iron until he has a mass approximately #aj or #ad lb4 in weight1 which he marvers into a pear-shaped lump by rotating the hot glass in the hollow of a wooden block4 ,he then blows the glass into a spherical bulb 7a71 which1 by quick rotation1 is widened and assumes a mushroom shape 7b74 ,another workman attaches a pontil to the outer centre of this bulb by welding it on with a small portion of hot metal4 ,the blow-iron is then detached by wetting and chilling the glass near to the blow pipe1 which breaks away1 leaving an opening in the bulb where it has become detached 7c74 ,this is then carried to an auxiliary heated furnace1 which has a wide opening emitting great heat1 and by resting the pontil upon a convenient support and rotating it quickly the action of centrifugal force and heat causes the glass to spread out at the opening1 which becomes larger and larger until the glass finally opens out into a flat circular disc of fairly even thickness throughout1 with the pontil still at the centre1 forming a bullion point or slight swelling1 due to the knob of glass used in affixing it 7d74 ,next1 the workman1 keeping the disc in rotation1 brings it away from the furnace and allows the metal to stiffen and set by cooling1 when it is carried to the annealing oven and detached from the pontil4 ,the discs are then stacked up for annealing4 ,when annealed1 these are afterwards cut across in sections or squares of convenient size by using a glass cutter's diamond4 ,illustration3 ,,four ,,stages ,,in ,,crown ,,glass-,,making ,it is evident that the centre portion1 containing the bullion point or bull's eye1 is useless for plain window glazing1 but occasionally these are sought after by glass decorators for use in coloured leaded lights for door panels1 etc4 ,sheet ,glass is made in the form of thin1 walled1 hollow cylinders of glass1 which are split along their length and round the cap and then opened out by heat and allowed to uncurl until each sheet lies out flat4 ,the workman gathers a sufficiency of glass upon his blow-iron by repeated gatherings1 and marvers it into a ball about as big as one's head4 ,this is blown out 7a7 and widened by rotating the blow-iron until he gets a mushroom shape 7b71 with a heavier bulk of glass at the extremity than at the sides4 ,illustration3 ,,six ,,stages ,,in ,,sheet ,,glass-,,making ,this extra thickness of glass at the extremity of the bulb tends to lengthen the bulb of glass as he swings it in a pendulum fashion1 and by blowing and swinging it alternately he gets an extended form 7c74 ,to permit the workman to swing the mass of glass out conveniently to the full length of the intended cylinder1 a long1 narrow pit or trench is provided below the floor level1 and by standing alongside this trench the workman is enabled to swing the glass within the trench at arm's length until the requisite length and width of cylinder are obtained4 ,this work requires a high degree of skill and strength4 ,the shape of the cylinder of glass is now as shown on page #ia 7d74 ,the extremity of this cylinder is now re-heated and opened with the aid of a spring tool with charred wooden prongs1 until the opening is enlarged and drawn out to the same diameter as it is throughout the cylinder4 ,it is now in the form of an open-ended cylinder 7e74 ,the cap of the cylinder at the blow-iron end is now cracked off4 ,a thread of hot glass is wrapped round the shoulder near the cap1 and the line chilled by using a curved1 hook-shaped rod of iron4 ,whilst the cap is being cracked off1 the cylinder is allowed to rest supported by a wooden cradle4 ,the cylinder is now open at both ends 7f7 and is taken to the flattening kiln or furnace4 ,this kiln has a level1 smooth floor1 heated from below1 upon which the cylinders are flattened out4 ,placing the cylinder on the floor in front of him1 the workman places along the inside length of the cylinder a long red-hot iron rod touching the glass1 and then chills the line with a touch from a cold iron rod4 ,this causes a split to take place along the whole length of the cylinder4 ,as these cylinders are split open1 they are removed to a hotter zone within the flattening kiln1 where the heat causes the cylinder to uncurl and gradually flatten out4 ,as the sheet becomes flat the workman levels it out with a flat block of charred wood called a polisher4 ,this is attached to a long handle1 and is rubbed over the face of the sheet of glass4 ,the weight of the wooden block is just sufficient to smooth out any creases and assists in levelling out any irregularities of the surface4 ,it is essential that the floor upon which the glass is resting should be perfectly smooth and level1 and uniformly heated4 ,as each sheet is levelled1 it is removed to the annealing oven and afterwards stacked up until cool1 after which the rectangular sheets are cut up to the various sizes required for window panes4 ,it is evident that the crown glass method gives more waste in cutting up1 and does not provide such large sheets as the cylinder method4 ,on the other hand1 cylinder glass always shows a certain amount of waviness on the surface1 and is not so brilliant as crown glass4 ,the better surface of crown glass no doubt is due to the fire-polishing it receives when being expanded out into the disc4 ,it appears to be somewhat difficult to get a perfectly smooth level face to cylinder glass by using the wooden polisher4 ,plate ,glass is used as mirror glass and in glazing shop windows and showcases4 ,it may vary between #a_/d and #c_/d in4 in thickness1 and is more expensive to produce than crown or cylinder glass4 ,in the manufacture of best plate glass1 the materials are melted in open crucible-shaped pots of varying sizes2 sometimes1 in making large1 heavy plate1 their capacity reaches #be cwts4 of metal4 ,when the metal is plain and clear from seeds it is either ladled out into smaller crucible pots for casting1 or1 as in the case of casting large sheets1 the whole crucible of metal is lifted bodily out of the furnace by means of a crane1 and1 after being skimmed1 is conveyed by an overhead travelling derrick to the casting table4 ,this table is a level iron bench the size of the plate to be cast1 the face of which consists of thick sheets of iron plate riveted together to form a level top2 along the whole length of each side of this table is a raised flange of a height sufficient to give the thickness of the plate of glass to be cast3 resting on these two outer edges a long1 heavy metal roller runs1 covering the full width of the table4 ,the crucible of hot metal is brought to a convenient position and the contents poured out on the table in front of the metal rollers4 ,these rollers then travel along and squeeze or roll out the hot metal over the surface of the table to the thickness regulated by the side pieces1 which also prevent the metal from flowing over the sides4 ,the empty crucible is then conveyed back to the furnace for refilling4 ,the cast plate of glass is then trimmed from any excess of glass at the ends1 and when set and stiff is lifted at one end slightly and pushed forward into a conveniently situated annealing oven1 where it is re-heated and subjected to a gradually diminishing temperature to anneal it4 ,the plate of glass1 as delivered from the annealing oven1 shows surfaces somewhat rough1 wavy1 and uneven1 from the marks left by the table and the roller1 and it has to be ground and polished level and smooth on both sides4 ,this is done by fixing one face of the glass plate in a plaster of ,paris bedding and setting it within a mechanical grinding machine4 ,this machine carries several revolving arms1 to which are attached other smaller plates of glass4 ,these are used as the rubbers1 a slurry or paste of sharp sand and water1 or abrasive powder1 being interposed between the two4 ,the revolving circular motion of the arms causes a grinding action between the two plates1 which wears down any irregularities and gives a more even face4 ,after this1 finer grades of abrasive materials are employed1 and1 finally1 polishing powder1 until the face of the glass plate is polished smooth and level4 ,the large plate of glass is then reversed and the process of grinding resumed on the other side4 ,much care is necessary in handling these large plates1 and every attention is necessary and devoted to get the largest pieces of plate without defects4 ,all portions showing defects have to be cut away1 and1 consequently1 reduce the size of the plate when finished4 ,in another method of making plate glass the molten metal is fed between two or more parallel rollers1 which are spaced apart to the thickness of the glass required 7about #a_/d in474 ,these rollers squeeze the glass out to a uniform thickness4 ,a roughly decorated surface is sometimes given to this glass intentionally1 by the metal rollers being indented with some form of set star pattern4 ,this glass is not ground or polished1 and is sold under the name of muffled or cathedral glass4 ,it is mostly used for roof lighting1 where the transparency may be somewhat obscured4 ,wired glass1 or strengthened plate1 is formed by embedding in the soft glass1 whilst being rolled1 a network of metallic wire of special composition to suit the temper of the glass4 ,this wire is fed from a separate roller into the space between the parallel rolls as the hot metal is fed in from either side4 ,it is necessary that the wire should be made from a metallic alloy which is not easily oxidised4 ,another method of strengthening plate glass consists in sealing together two plates with an intersecting film of celluloid4 ,a decorated coloured rolled plate is made for use in leaded lights by mixing portions of several differently coloured glasses together in a small pot and slightly agitating the contents so as to intermix the respective colours4 ,when the glass is rolled out1 a pretty agate or marbled effect is obtained1 due to the distributed coloured glasses becoming intermixed4 ,as a rule1 these glasses are more or less opalescent1 and are only used for decorative purposes1 church lights1 etc4 ---------------------------------------- -------------------------------- ,,chapter ,,xiii ,,tube1 ,,cane1 ,,and ,,chemical ,,glassware ,laboratory and chemical glassware consists of thin blown ware in the form of flasks1 beakers1 test tubes1 etc41 used in chemical operations4 ,most of these goods are blown in hinged moulds mechanically or automatically operated by the worker4 ,the lips and flanges of the necks are neatly formed afterwards by re-heating and working the edge to a form allowing them to pour cleanly1 and prevent any fluid contained therein from running down the sides of the flask or beaker whilst in use4 ,the heavier glassware1 in the form of desiccators1 measuring cylinders1 specimen jars1 and three-necked bottles1 are made by handwork4 ,chemical apparatus has necessarily to be made from a permanent stable highly refractory glass1 so as to resist the solvent actions of mineral acids1 alkaline solutions1 and boiling water1 as well as sudden changes in temperature4 ,the manufacture of tube and cane glass for various purposes forms a large and extensive portion of the glass trade4 ,considerable quantities of tube and cane glass in various sizes are used by lamp workers in the manufacture of certain forms of chemical apparatus and filling electric light bulbs4 ,by re-heating glass tube and working before a blow-pipe flame1 the various forms of test tubes1 pipettes1 burettes1 soda-lime ,u-tubes1 and condensers are made4 ,generally1 for chemical apparatus two classes of tube are made1 one a soft soda tube1 and the other hard combustion tubing4 ,particular care has to be devoted to the grading and sorting of the various sizes4 ,the bore of the tube1 the thickness of the walls1 and the outside width have all to be checked and the lengths classed accordingly4 ,in the manufacture of tubing1 unless the glass is of large size or great thickness1 it is not annealed1 and shows a case-hardened condition which materially increases the strength of the tube to resist internal pressure1 as is the case with boiler gauge tubing4 ,in the manufacture of apparatus from tube and cane1 care must be taken that the various pieces used in welding together the different portions of the apparatus should be of the same temper and composition1 and supplied from one source1 so that they may join and work perfectly together4 ,the lamp worker or glass blower should take care to get his supplies from a reliable source1 so that the glass pieces will be adapted to work together4 ,trouble occurs when odd tubings from various makers are worked together4 ,the same applies to fancy glass working1 where various coloured canes are worked into ornaments4 ,reputable firms can always supply from stock such colours and tubing properly adapted for their specific purposes1 and they take every precaution to see that the various colours join and work together4 ,supplies of glass rod can be had that will join on to platinum1 nickel1 iron1 or copper wire with sound joints4 ,in making cane glass1 the workman gathers sufficient metal upon a pontil3 for thin cane he would gather less than for heavy thick cane4 ,after gathering1 he marvers the metal into the form of a solid cylinder4 ,meanwhile1 an assistant gathers a little metal on a post or pontil with a flattened end4 ,the metal he has gathered has covered the flat end of the post1 and he holds this in readiness for the workman1 who is now re-heating the cylinder of glass at the pot mouth4 ,as the cylinder of glass becomes soft1 he withdraws it and allows the end of the cylindrical shaped mass of glass to fall gently upon the flat end of the post1 to which it adheres4 ,they then carry the glass between them to a wooden track or run-way1 along which they walk at a smart pace in opposite directions2 stretching out the hot glass between them1 it gradually thins out and rests on the floor4 ,the pace the men separate apart from each other is regulated according to the thickness of the cane desired3 for very thin cane a smart trot is necessary1 but for a thick cane a slow walk is sufficient4 ,as the glass is drawn out it is allowed to rest on wooden supports1 and when cool is cut up into convenient lengths by scratching the glass with a steel file4 ,these lengths are collected and bundled up for sorting and classification4 ,all portions distorted or over-size are returned as cullet for re-melting and re-use4 ,in tube making1 instead of a solid cylinder as in cane making1 the workman1 by gathering the glass on a blow-iron and blowing and marvering it1 obtains a thick-walled1 hollow1 cylindrical form4 ,this is re-heated and the end stuck to a post and drawn apart as before described in cane making1 forming a tube of a width proportional to the rate the two have travelled apart in drawing it out1 and to the quantity of metal gathered4 ,in this way the respective sizes and thicknesses are regulated4 ,a narrow cane or tube may be drawn out for #cjj ft41 but for a thick or wide one probably only #cj ft4 may be drawn4 ,in making the larger widths1 some method of cooling1 or fanning1 is adopted1 to ensure uniform size by cooling the hot glass quickly as it is drawn out4 ,it is evident that1 whatever shape is given to the original mass of glass whilst being marvered1 the tube will bear a similar shape in proportion1 either within or outside the glass4 ,in this way1 square1 triangular1 or oval sections can be produced in both tube and cane4 ,the manufacture of white opal1 coloured cane1 and tube is carried out on like methods to those used in ordinary cane and tube making4 ,we will now describe the manufacture of ,filigree4 ,this is rod or tube containing opal or coloured threads1 either straight1 spiral1 or interlaced within a transparent glass2 these threads follow the whole length of the cane or tube4 ,this curious form of glasswork was originated by the ,venetians1 who are exceptionally skilled in producing some elegant and ornamental filigree decorated glassware4 ,the method of producing filigree cane consists of first taking a number of short lengths of opal or coloured cane previously drawn and cut to about #f in4 lengths4 ,these are then placed in vertical positions around the inner circumference of an iron cup mould1 which may be about #e in4 in diameter4 ,the opal strips of cane are supported vertically in small recesses provided in the rim of the mould at equidistant intervals4 ,a ball of hot crystal glass is gathered on a pontil and is lowered into the inside of the mould1 the hot metal coming in contact with the opal strips of glass adheres to them1 and upon withdrawing the glass it brings the opal strips away with it arranged in sections round the circumference of the ball of glass4 ,this is now re-heated and marvered until the canes or strips of opal are well embedded in the hot glass4 ,then the workman gathers another coating of hot glass over the whole1 marvers it again into a cylindrical form1 and then proceeds to draw it out as described in cane making4 ,if a spiral form of lines is desired1 the workmen1 whilst drawing out the cane1 turn or twist the pontil and post in contrary directions4 ,these rotations cause the opal veins or threads to assume a spiral or twisted form within the glass4 ,various coloured cane may be used in the above process1 and by placing them in alternate positions to the opal strips within the cup mould some very pretty and curious filigree work is obtained4 ,these twisted filigree canes are used and manipulated over again in the process of making the various ,venetian goblets and wine stems4 ,some fine effects in the application of filigree decoration can be seen in the specimens of ,venetian glassware exhibited in the ,british ,museum4 ,millefiore work is produced by the workman1 first spreading a layer of an assortment of small coloured glass chips of varying sizes 7between #a_/h and #a_/d in4 cube7 over the face of the marver1 and then taking a gathering of crystal metal on his blow-iron and rolling the ball of hot glass into the coloured mixture on the marver4 ,the hot glass collects up a coating of the coloured chippings1 and is then re-heated and again marvered1 another gathering of crystal metal is made1 which incases the whole4 ,this is then blown out and worked into some form of ornament1 such as a paper weight1 inkpot1 or bowl1 producing a curious result that shows blotches of colours embedded within the glass1 the effect of which is increased if a backing of opal glass has been used in the first gathering3 this shows the coloured effect against a white background4 ,spun ,glass4 ,another curious form of glass is the spun glass which is much employed in making fancy ornaments4 ,glass can be spun into a thread so fine and flexible that it can be worked into a fabric like any textile material4 ,in this way1 glass ties can be made by plaiting the spun glass threads into the required form4 ,spun glass fibre is used in making the brushes used for cleaning metals with acids4 ,on account of its greater resistance to acids than is shown by ordinary cloth1 an endeavour is being made to use spun glass cloth in certain industries as a commercial application4 ,spun glass is used for making a form of filter cloth which is being used successfully in filtering acid residues in certain chemical processes1 and1 no doubt1 when the elasticity and strength of the glass threads can be more developed1 the scope for its use in other industrial processes will be increased4 ,the method of making spun glass thread consists in melting the end of a plain or coloured glass rod 7which may be square1 round1 or triangular in section7 in a blow-pipe flame and grasping the end which is melting with a pair of pincers1 drawing it out and affixing it to a wooden drum1 which is turned rapidly away from the glass being heated4 ,the drum may be #b or #c ft4 in diameter1 and as the glass is continually fed into the heat it is drawn out into a very thin thread by the rapidly revolving drum1 and coiled up until a sufficient quantity has been obtained4 ,the thread is then cut across the drum1 collected1 and used for plaiting or braiding into the fabric or cloth4 ,the iridescence and variety of colours yielded by the refraction of light between the glass threads gives spun glass its peculiar effect1 very evident in the forms in which it is used in decorating small ornaments such as forming the tails of glass birds4 ,glass wool is made in a somewhat similar way1 and is successfully used as a non-conductive packing material for insulation from heat4 ,glass frost or snow is made by blowing small gatherings of glass out to a bursting point4 ,these very thin shells are then crushed and the flakes collected1 and used for such purposes as surfacing sand paper or decorating ,christmas cards1 being sieved to the requisite size and affixed with a siccative to the paper4 ,dolls' eyes and artificial human eyes are made by well-trained operators working before a blow-pipe flame and manipulating tube and cane of delicately coloured tints to form the pupil and shell of the eye1 the veins being pencilled on with thin threads of red-coloured glass4 ,a considerable amount of skill and adaptation is necessary to do this class of work1 and much depends upon the matching of the coloured cane glass used to give the natural effects4 ,when properly made1 so clever and natural are these glass imitations of the human eye that it is with difficulty that the ordinary observer can tell that they are not real4 ,a skilled worker will make the artificial eye to fit the muscles of the socket and so move4 ,in this way much ingenuity has been shown in fitting the eye sockets damaged during the war4 ,aventurine is a golden coloured glass containing minute yellowish spangles or crystals reflecting upon each other and giving its peculiar effect4 ,this glass is obtained by the use of an excess of copper with strong reducing agents in the glass1 whereby the copper is partially reduced within the glass1 giving the pretty spangled effect4 ,this glass is often used in the form of jewel stones1 being cut and polished and fitted in ornaments4 ,the process of making this glass was originated by the ,italians1 and for some time it remained a secret with them1 and even now is styled 8,italian aventurine40 ,chrome aventurine is another form1 giving a green1 spangled effect4 ,this is got by using an excess of chromium in the presence of reducing agents4 ,the successful production of aventurine depends upon slowly cooling the molten glass so as to assist crystallisation4 ,mica schist1 or flake mica1 is used to give another curious effect in glass4 ,a gathering of some dark-coloured glass is rolled or marvered upon a thin layer of flaked mica1 and then a further gathering or coating of clear crystal metal is made4 ,the whole is then blown and formed into some fancy ornament or vase4 ,when finished1 the glistening mica flakes show through against the coloured background1 giving a curious silvery reflection4 ---------------------------------------- -------------------------------- ,,chapter ,,xiv ,,optical ,,glass ,the manufacture of optical glass forms a very important section of the glass industry1 and presents some of the most difficult problems the glass maker has to deal with4 ,it is in this section of the glass trade that applied physical and chemical science becomes of the utmost importance to the manufacturer4 ,the production of optical glass is impeded by any defects which become evident in the structure of glass when examined under a polariscope4 ,the presence of any striae1 seeds1 or stresses within the structure of the glass disqualifies it for any important optical work4 ,it is a difficult matter to get pieces of optical glass only a few inches in diameter of the right optical constant and refractive index that are homogeneous enough to allow of the light rays passing without some dispersion when set up for use4 ,it becomes necessary1 therefore1 to achromatise one glass with another in the form of doublets to correct aberration4 ,a high degree of transparency and durability is necessary in all optical glasses4 ,the persistent evidence of stresses developed in the solidification of the glass upon cooling1 even when the glass is slowly and carefully annealed1 is a most difficult factor to deal with4 ,in annealing optical glass1 the various temperatures and time periods have to be delicately adjusted and controlled1 or big losses result4 ,even then many efforts may be made before a suitable piece of glass is obtained1 and the costs keep accumulating with each attempt1 and some idea of the amount of labour involved in the undertaking to produce optical glass at once becomes evident4 ,the use of decolorizers and impure materials is not permissible1 on account of the absorption and consequent resistance to the passage of light rays4 ,the annealing1 instead of occupying one or two days1 is sometimes extended over a course of ten or fifteen days1 in order gradually to relieve any stress present4 ,the pots in which the glass is melted may only once be used1 as the glass is usually allowed to cool down gradually and undergo the process of annealing within the pot4 ,the temperature of the furnace is controlled by regulating the draught by means of dampers in the main flues1 arranged to act so as to carry out the annealing of the glass within the furnace4 ,the regulation of the temperature within the furnace is of the greatest importance2 if too hot the glass dissolves the clay of the pot1 and if retarded too much it gives difficulty in freeing the metal from seeds1 and plaining or fining the glass properly4 ,small furnaces containing one or two pots give the best results4 ,these furnaces are worked on an intermittent process of first melting the glass and then gradually cooling to anneal the glass within the pots in mass1 the furnace being allowed to die out gradually4 ,when cool1 the pots are broken away from the glass1 which is then cleaved into lumps4 ,each lump is carefully examined for any defects and the best pieces selected for re-annealing4 ,these are afterwards ground to the desired shape in the form either of a lens or prism4 ,the chances are that not many pieces of perfect glass can be obtained from each pot of metal1 and probably out of a whole pot only a fifth would be suitable for use after the process of selection and cleaving has taken place4 ,in the manufacture of optical glass1 batch materials are chosen that do not differ greatly in specific gravity4 ,every effort is devoted to obtain the purest materials possible2 the batches are finely ground and well mixed before melting4 ,the glass-melting pots should be made of the purest and most refractory obtainable in order to prevent the solution of any impurities into the glass whilst it is melting4 ,in heating the pots for melting optical glasses every endeavour is made to heat them equally all round the top1 bottom1 and sides1 so as to dissolve all portions of the glass evenly and completely together4 ,at times the melted glass is stirred with a bent iron rod encased in a porcelain tube1 and the glass agitated in order thoroughly to mix the components whilst fusing1 and keep the composition of the glass as uniform as possible4 ,after the metal has melted and plained clear from all seed and cords1 the pot of metal is annealed1 and when cooled the glass is extracted in lumps and examined for any defective pieces1 which are rejected4 ,the selected pieces are afterwards ground to the desired shape and1 if necessary1 re-annealed4 ,in this process the pots being used only once1 are expensive items1 and they considerably increase the cost of production4 ,before the war the optical glass trade was confined to a few firms in this country1 who supplied only a fraction of our needs4 ,we have been dependent mostly upon continental supplies of optical glass1 and it is only quite recently that ,government state assistance has been forthcoming in giving scientific aid to manufacturers by investigating and reorganising this section of the glass industry4 ,it is to be hoped that this state assistance will continue1 and that the optical branch of the glass trade will be perfected to such an extent that we may in future be independent1 and produce for ourselves all the optical glass requirements of our navy and army4 ,it is to be regretted that this industry did not receive state assistance before the war4 ,if it had1 we should certainly have been better prepared and equipped than was the case at the start of the ,great ,war4 ---------------------------------------- -------------------------------- ,,chapter ,,xv ,,decorated ,,glassware ,certain methods of decorating glass are carried out whilst the glass is being made by the workmen4 ,other methods consist in decorating the glass after it has been made1 such as cutting1 fluting1 etching1 engraving1 and enamelling4 ,in another form of decoration the method consists of a combination of two or more of the above processes4 ,the crystal glass may be cased over with a thin covering of coloured glass by the glass worker1 and this outer coloured casing cut through by the glass cutters1 exposing and showing through the colourless crystal underneath with very effective results4 ,a small portion of coloured glass1 such as citron green1 topaz1 blue1 or ruby metal is gathered from the pot by an assistant1 and the workman1 gathering a ball of crystal glass on his blow-iron1 allows a portion of the coloured metal held by the assistant to fall or drop upon the ball of crystal4 ,upon blowing the whole out1 the coloured metal is spread as a thin casing upon the outside of the bulb of crystal4 ,this bulb is then worked into a wine-glass or other article1 which1 after annealing1 is sent to the glass cutter1 who decorates the outer surface by cutting the glass on his wheel4 ,the colourless glass then shows through against the coloured surface where it has been cut to the pattern1 the colour standing out in relief4 ,in another form of decoration1 the workman allows small pear-shaped tears or drops of coloured glass to fall upon the outer surface of a bowl or vase1 in equidistant positions round the circumference of the article1 ,by placing and working the coloured glass into position in this way1 some pretty artistic results are obtained1 dependent upon the skill and artistic taste of the workmen4 ,in another method of decoration1 certain coloured glasses are used1 the composition of which causes them to turn opalescent upon re-heating the glass to a dull red heat4 ,the re-heating of the tops of crimpled flower vases made from such glass gives pretty results1 showing a gradual fading opalescence1 extending from the top edges to a few inches down the vase1 into a clear coloured glass at the foot of the stand4 ,a similar effect1 without the opalescence1 is obtained by the workman gathering a small piece of coloured glass on the tip of his blow-iron1 and then taking a further gathering of clear crystal metal4 ,the whole is then blown out and worked into a vase or wine-glass1 thus obtaining a coloration denser at the top edges1 where the vase or wine-glass has been sheared off1 and gradually fading away to a colourless glass a few inches towards the foot1 which is clear crystal4 ,there are also certain compositions which1 when worked into a vase1 and re-heated on the edges1 strike or turn to a colour such as pale blue or ruby4 ,these are self-coloured glasses1 in which the colouring remains latent until the glass is re-heated1 like the opalescent glasses4 ,in these glasses the composition is the more essential factor4 ,glass cutting is an effective way of decorating glassware4 ,in using this method1 the crystal glassware is made fairly heavy and strong1 so as to permit of the deep cuttings which refract the light and show up the prismatic patterns so brilliantly4 ,illustration3 ,,machine ,,for ,,smoothing ,,bottoms ,,of ,,tumblers ,in cutting glassware1 the glass cutter works in front of a rotating disc of iron carried in a frame4 ,this wheel has a bevelled edge upon which a fine jet of sand and water is allowed to drip from a tundish above4 ,the abrasive action of the sand cuts into the glass1 and the workman1 by holding the glass dish or bowl against the wheel1 follows the design or pattern in diagonal lines across the article4 ,these cuttings are recrossed1 and the intermediate diamond spaces filled in with lightly cut set patterns1 until the whole of the intended design is 8roughed0 out over the surface of the glass1 after which the glass is taken to another frame carrying a stone wheel1 which is of much finer abrasive action4 ,this stone wheel smooths the rough cuts done by the previous wheel4 ,after this the cuts are polished successively on a wood wheel and brush with polishing powders1 until a smooth and polished cut is obtained4 ,as the value of the glass is greatly increased by cutting1 only the best and clearest articles of table glass are so treated4 ,the work of cutting becomes technical and expensive1 according to the richness of the cutting demanded4 ,the crystal table glass made from lead gives the most brilliancy in cutting4 ,soda-lime glasses are found to be hard to cut and do not give such brilliant and prismatic effects as the glass made from lead compositions4 ,an automatic machine for grinding1 smoothing1 and polishing the bottoms of tumblers1 etc41 8bottoms0 or grinds1 smooths1 and polishes tumblers at the rate of #b1jjj a day4 ,four vertical revolving wheels are fixed within a frame1 one iron1 two stone1 and one wood4 ,over each of these is a rotating spindle carrying the tumbler so that the bottom of it is automatically pressed against each vertical wheel in turn4 ,the first wheel does the roughing1 the two next the smoothing1 and the fourth the polishing4 ,these machines are simple and require only unskilled labour to operate1 and go far towards cheapening production4 ,glass engraving and intaglio work is a much lighter and more artistic method of decorating glass than the deep cutting before described4 ,in these processes the glass is cut or ground to a less extent1 and a more free treatment of design is possible4 ,floral ornamentation and natural forms of applied designs can be carried out1 and portions may be left rough or polished1 according to the effect of light and shade required4 ,the workman1 whilst engraving1 works before a small copper or metal wheel rotating in a lathe1 and uses fine grades of emery or carborundum powders made into a paste with oil1 as the abrasive medium4 ,the frame turning these wheels is like a lathe1 and may be worked by a foot treadle4 ,the wheels are interchangeable1 and an assortment of various sizes1 having different bevelled edges1 is kept at hand in a case1 from which the engraver selects the one most suitable for the particular work to be done4 ,glassware for engraving and intaglio may be made much lighter than that required for cutting4 ,etching is a method of decorating glass by the chemical action of hydrofluoric acid4 ,this acid in its various combinations attacks glass1 decomposing its surface and giving a dull or semi-matt effect4 ,only those portions of glass which constitute the design are exposed to the acid paste or fumes4 ,the other portions are protected by a covering of beeswax1 which is unaffected by the acid and protects any portions covered by it4 ,illustration3 ,,glass ,,engraving ,the process carried out is varied in many ways4 ,in some cases pantograph and etching machines are introduced to give the designs4 ,a warm copper plate1 with the design or ornament engraved thereon1 is covered with a wax paste1 and the surplus cleaned off with a palette knife or pad of felt1 leaving the paste in the recesses of the engraving2 a piece of thin tissue paper is laid over the engraved plate and takes an impression of the design in wax4 ,this tissue is then transferred to the glass to be decorated1 the wax design adheres to the glass1 and the paper is drawn away4 ,a further resist or coating of wax is painted round the design to protect the rest of the glass1 and a paste composition giving the action of hydrofluoric acid is applied1 which after a short time eats into the exposed portions of glass4 ,after another short interval1 it is washed off1 and the wax coating removed by washing the glass in hot1 soapy water4 ,the design then appears in a matt state against the clear1 unattacked glass4 ,the mechanical method of etching the design is carried out by first dipping the whole glass into a bath of hot liquid wax1 allowing a thin coating to set and cool upon the surface of the glass4 ,the article is then introduced into a machine which has a number of needles1 worked by sliding gears in an eccentric fashion4 ,these needles are adjusted just to scratch away the thin coating of the wax into a design1 and expose the glass in the form of a decorated scroll or band round the glass4 ,the glass is then dipped into a vat or bath of dilute hydrofluoric acid for a few minutes1 after which it is removed and washed1 and the wax recovered by heating the glass upon a perforated tray1 when it melts and runs off the glass1 and is collected for further use4 ,the article is then washed and cleaned and shows the scroll or etched portions where the needle has traced the design4 ,another effective result is obtained by etching a design on the back of a plate glass panel4 ,after cleaning and silvering or gilding the back1 the design appears in a matt silver or gilt lustre upon viewing it from the front of the mirror4 ,glass which has been sand-blasted has a similar appearance to etched glass1 but a rather coarser surface4 ,the portions of the glass plate to be decorated are exposed to the action of a blast of air1 into which fine1 sharp-grained quartz sand is automatically fed4 ,an abrasive action1 due to the force with which the particles of sand are blown against the glass1 takes place1 rendering the surface opaque or matt4 ,this method is generally adopted in printing trade names or badges upon bottles1 etc4 ,a stencil of parchment or lead foil is cut out to form1 and used to protect the glass and resist the abrasion where required4 ,rubber gloves are worn by the operator4 ,the work of sand-blasting is executed within a small enclosed dust-proof chamber fitted with glass panels4 ,the operator manipulates the glass through openings in the sides of the chamber4 ,the air blast is supplied by a motor-driven air compressor and is regulated by a foot pedal4 ,the action is very sharp and quick1 and is a cheap and effective way of badging hotel glassware and proprietary bottles4 ,glassware may be decorated by being enamelled with coloured enamels4 ,in this method of decorating1 soft1 easily-fused1 coloured enamels are used1 containing active fluxes such as borates of lime and lead1 which melt at low temperatures4 ,these enamel colours are prepared by being fused and then ground to fine powders1 which are mixed with a siccative or oil medium1 and painted upon the glass4 ,the painted ware is then heated within a gas or wood-fired enamelling furnace or muffle1 until the painted designs are melted and fused well upon the glass4 ,the glass is re-annealed in cooling down the muffle4 ,for this form of decoration1 a hard refractory glass is required that will not soften easily under the heat of the muffle2 otherwise the glassware becomes misshapen too easily under the heat necessary to flux or fuse the enamels properly4 ,a form of staining glass is also practised which consists of applying compositions containing silver salts to portions of the glass and firing at a low heat4 ,the silver stains the glass a deep yellow4 ,the colour may be varied by the use of copper salts1 when a fine ruby stain is obtained wherever applied4 ,iridescent glassware is produced by several methods4 ,sometimes a small proportion of silver and bismuth is added to a coloured glass batch1 and by manipulating the resulting glass in a carbonaceous flame the silver is partially reduced within the glass1 forming a pretty iridescent reflection on the glassware4 ,by a suitable adjustment of the oxygen content in the composition of such glasses1 the iridescence can be regulated to such an extent that the slightest flash or reducing influence gives a beautifully finished lustre over the ware4 ,iridescence can also be formed by re-heating crystal glassware within a chamber in which salts of tin1 barium1 aluminium1 and strontium are volatilised4 ,this method produces a superficial iridescence which is not quite so permanent as the previous process4 ,glass ,silvering4 ,the silvering of mirrors is carried out by taking a thoroughly cleaned plate of polished glass and floating one surface in a solution of silver nitrate1 to which a reducing agent is added4 ,the silver is thereby precipitated or deposited in a thin lustrous film upon the glass1 which causes reflection by the rays of light striking against the silvered background4 ,after silvering1 the back of the plate is coated with a protecting paint or varnish1 which dries and preserves the silver deposit and gives it permanency4 ,in the manufacture of fancy ornaments1 such as birds1 hat pins1 and small animals1 various coloured glass cane and tube are worked together by the operator melting and welding the respective colours together before a blow-pipe flame1 the tails of the birds being formed by sealing in a fan of spun glass into the body of the bird1 which has been blown out and formed from a piece of tube4 ,some very curious ornaments are formed in this way4 ,glass buttons1 pearl1 and bead ornaments are formed by working cane and tube of various coloured compositions before the blow-pipe1 sticking and shaping the various forms on to wire4 ,mosaic glass decoration is used in jewellery in a mural or tessellated form4 ,in this method small cubical or other shaped cuttings of various coloured opaque glass are inlaid in mastic cements or pastes to form the design1 the face being afterwards ground and polished smooth1 and mounted or set within the ornament4 ,larger cuttings may be inlaid in cement for pavement or mural decoration4 ---------------------------------------- -------------------------------- ,,chapter ,,xvi ,,english ,,and ,,foreign ,,methods ,,of ,,glass ,,manufacture ,,compared ,the continental methods of glassmaking differ so much from the ,english methods that a few remarks giving comparisons will be of interest4 ,it is noticeable that chemical and engineering science is more thoroughly applied in the manufacture of glassware abroad4 ,their method of specialising wherever possible1 and the introduction of mechanical and automatic machines have done much toward increasing their production and efficiency4 ,the flourishing and extensive state of glassmaking abroad is shown by the size and extent of the glass works1 some of which work as many as forty or fifty furnaces and employ #c1jjj to #e1jjj hands4 ,gas-fired regenerative or recuperative furnaces are more generally used1 which permit higher temperatures1 cheaper metal1 and greater economy in fuel and labour4 ,the present type of ,english furnace is very wasteful1 and even with good fuel it is difficult to maintain high temperatures and regularity in working4 ,our method of firing1 raking1 and teasing is very exhausting to the workmen in attendance4 ,in many ,english glass works1 especially those in the ,stourbridge district1 it is the practice to fill the pots on a ,saturday morning and take until the following ,monday night to melt and plain the glass1 no glassware being made for three days of each week4 ,starting on ,monday night or ,tuesday morning1 the glass makers work in six hour shifts day and night until ,friday night or ,saturday morning1 when the pots are again filled and the weekly course starts over again4 ,abroad the pots are filled nightly and hold just sufficient metal to last out the work during the day1 and are built of a capacity to suit the articles being made4 ,the disadvantages of our method are obvious when a comparison is made with the continental method of melting the glass nightly and working it out daily1 especially when the efficiency or output of the furnaces as compared with their fuel consumption is taken into consideration4 ,abroad the furnaces are small and compact2 they take up less floor space1 yet they are far greater in efficiency4 ,as they are gas-fired1 the combustion is more complete1 and by the use of regenerators or recuperators greater heat is available for melting the glass quickly4 ,larger proportions of sand are used in the glass mixtures1 which1 being the cheaper component1 cheapen the production of their glass wares4 ,owing to the more perfect combustion which takes place within the chambers of gas-fired furnaces abroad1 lead glasses are successfully melted within open crucible pots4 ,when the heat comes into direct contact with the batch materials being melted1 it does its work quicker and with less fuel consumption than is the case if it has first to be conducted through the hood of covered pots which have necessarily to be used in the old ,english type of furnace4 ,it is particularly noticeable that the glass workers abroad do not spend so much time upon producing an article as is usual under the ,english method of working4 ,by the extensive use of moulds fitted to mechanical contrivances operated by the foot1 their work is expedited and made simple and easy4 ,technological education in the glass industry abroad is more thorough and general4 ,the glass workers1 not having to work at night1 have the evenings free for recreation and education4 ,it would do much towards developing the ,english glass trade if night work for boys could be abolished4 ,the adoption of the continental system of melting the metal during the night and working only during the day 7by using gas-fired furnaces7 would do much in this direction4 ,one cannot expect the youths of the glass trade1 who have to work during nights1 to attend the evening classes for educating themselves1 without a severe strain upon their constitutions4 ,this fact partially accounts for the repeated failure to establish technical classes and trade schools in the glassmaking centres of this country4 ,the conservatism and lack of support from the glass manufacturers themselves account for much of the slow progress and development of the trade4 ,as a rule1 it will be found that the manufacturers have everything to gain by the better technical education of their employees4 ,it is with pleasure we notice that a few at least are now taking this broader view and giving such schools their hearty support and financial aid4 ,in the glassmaking centres abroad there are established state-aided technical and trade schools1 where1 for a small nominal fee1 the youths of the glass works are trained and taught the principles of their industry4 ,apprenticeship in the factories then becomes unnecessary4 ,the working hours abroad are usually sixty hours a week 7ten hours a day71 compared with the ,english forty-four to fifty hours' week 7six hour shifts74 ,the trade unions of the glass workers abroad are more progressive1 and their officials do not interfere with the manufacturers' endeavours to increase efficiency and cheapen production by introducing machinery4 ,the promotion of the workpeople goes by merit1 and not by the dictation of the trade union officials1 as is too often the case in this country4 ,here1 very little sentiment or good-fellowship exists between the glass workers' union and the employers1 and in its place the rank officialdom of unionism has become so evident as to be a bar to the progress of the industry4 ,instead of assisting the progress of the trade1 and mediating in cases of dispute1 the union appears to exist as a buffer of antagonism between the glass workers and their employers4 ,many a capable youth in the glass trade here has been kept back from promotion to a better position solely by the dictation of the union to which the men belong4 ,cases are known where the union have restricted the workman's output when he may be working under piece rate4 ,the best inducements may have been offered him by the employer to increase his output1 and1 although the workman may be willing to accept the master's terms1 we find a union official stepping between them1 and fixing the maximum number of the articles that shall be made in his six hour shift4 ,usually1 this fixed quantity is got through in four hours1 yet the workman is not allowed to make more than the stipulated number fixed by the union1 or he is fined4 ,another incredible fact is that the employer here1 when in need of a workman1 is not allowed to choose his own men4 ,he must apply to the union1 and the man remaining longest on the society's unemployed book is then sent to him4 ,whatever his inefficiency may be1 the employer is bound to take him2 if he employs anyone else1 a strike results4 ,such action is despotic and shows up the worst features of trade unionism that can possibly be conceived4 ,the ,english glass industry has been repeatedly disorganised by this obstinate attitude of the glass makers' union1 and a consequence is that the foreigner has seized the opportunity to step in and increase his market1 to the detriment of our own trade2 with this extended market1 increased output1 and cheaper production1 the foreigner undersells us in our own country4 ,it is to be hoped these adverse conditions will soon be remedied and the ,english glass industry restored to a more flourishing state by the prompt and united action of the men and masters1 realising the gravity of the position and acting accordingly4 ---------------------------------------- -------------------------------- ,,appendix ,,journals ,,and ,,books ,,for ,,reference 8,american ,pottery ,gazette40 7,new ,york1 ,u4,s4,a47 8,boswell's ,memoir on ,sands ,suitable for ,glassmaking40 7,longmans1 ,green ,co41 ,london47 8,pottery ,gazette40 7,scott ,greenwood1 ,london47 8,sprechsaal40 7,coburg1 ,germany47 8,painting on ,glass and ,porcelain40 ,hermann4 7,scott ,greenwood47 8,decorated ,glass ,processes40 7,constable1 ,london47 8,jena ,glass40 ,hovestadt4 7,macmillan ,co47 8,glass ,manufacture40 ,rosenhain4 8,producer ,gas-,fired ,furnaces40 ,ostwald4 8,glassmaking40 ,by ,a4 ,pellatt4 7,bogue1 ,london47 8,gas and ,coal ,dust ,firing40 ,putsch4 7,scott ,greenwood47 8,the ,collected ,writings of ,h4 ,seger40 7,scott ,greenwood47 8,ceramic ,industries40 ,vol4 ,i4 ,by ,mellor4 8,modern ,brickmaking02 8,british ,clays1 ,sands1 and ,shales02 8,handbook of ,clay ,working40 ,by ,a4 ,b4 ,searle4 7,griffin ,co47 8,glass ,blowing40 ,by ,shenstone4 8,asch's ,silicates of ,chemistry and ,commerce40 8,clays40 ,by ,a4 ,b4 ,searle4 7,pitman1 ,london47 8,fuel and ,refractory ,materials40 ,sexton4 7,mackie ,sons47 8,furnaces and ,refractories40 ,harvard4 7,mc,graw1 ,new ,york7 ,,societies' ,,journals ,,and ,,transactions 8,the ,society of ,glass ,technology40 7,sheffield47 8,the ,american ,ceramic ,society40 7,columbus1 ,ohio1 ,u4,s4,a47 8,the ,english ,ceramic ,society40 7,stoke-on-,trent1 ,staffs47 8,journal of the ,society of ,chemical ,industry40 7,westminster1 ,london47 ---------------------------------------- -------------------------------- ,,index ,aberration1 #ajd ,acids1 action of1 on glass1 #ah1 #ai ,action of glass on 1 #de ,alkali1 #bc ,alumina1 #i-aa1 #bj ,amethyst1 #ca ,analysis of 1 #cg ,ancient glass1 #a ,annealing glass1 #ah ---- pots1 #ff ,arsenic1 #ca ,artificial eyes1 #aja ---- cements1 #bd ---- pearls1 #ca ,aventurine1 #bb-ajb ,barytes1 #h-bf ,basalt1 #aj ,bastie's ,process of hardening glass1 #ah ,batch1 #aa-ac ,beads1 #ca-aaf ,black glass1 #bi ,blowing glass1 #hj1 #hb ,blow-iron1 #hj ,blue glass1 #bh ,bohemian glass1 #be ,borates in glass1 #g1 #h1 #i ,boric acid1 #g ,bottle glass1 #bf1 #bg ,bottle-making1 #gg1 #gi ,bull's eye1 #ij ,buttons1 #aaf ,cane1 #ig ,capacity of pots1 #ea-eb ---- of tank furnace1 #ef ,carbonate of soda1 #f ,cements1 #bd ,chain screen1 #fh ,chair1 ,glassmakers'1 #ha ,chemical properties of glass1 #d-ae ,chemical ,formulae1 #ab ,chimneys1 ,lamp1 #af ,clays for pots and furnaces1 #cf ,coloured glasses1 #bh1 #bi ,colour of silicates1 #aa-bb ,complex glass1 #bf ,composition of glass1 #d-be ,compound glasses1 #be ,conductivity of glass1 #bc ,continental glass1 #c1 #hh1 #aah ,covered pots1 #ba-bg ,cracking-off glass1 #ae1 #ag1 #he ,crown glass1 #bf-hi ,crucible pots1 #ba1 #bg1 #fd ,cullet1 #aj1 #he ,cutting glass1 #h1 #aj1 #af ,decay in glass1 #b ,decomposition1 #b1 #ai ,decorated glass1 #ajh ,decolorants1 #cb ,defects1 #i1 #bc1 #cd ,de-grading glass1 #bc ,density1 #af ,devitrification1 #c1 #h1 #bj ,discovery of glass1 #a ,doll's eyes1 #aja ,education1 ,technical1 #abj ,electric furnaces1 #eh ,emerald1 #ca ,enamelling glass1 #aae ,english type of furnace1 #dc ,engraving glass1 #aaa ,etching1 #ai-aab ,expansion1 ,thermal1 #af ,eye of furnace1 #dc ,eyes1 ,artificial1 #aja ,fancy glass1 #aaf ,filigree1 #ii ,fire-clay1 #c1 #aa-cf ---- analyses1 #cg ,fire-clay1 blocks1 #ci1 #de ----1 ,burnt1 #ci1 #da1 #fa ---- crucibles1 #fd ----1 ,grinding of1 #ci ----1 ,melting point of1 #fd ----1 ,mild1 #ci1 #fe ---- pots1 #fb ----1 ,properties of1 #cf-ch1 #da ---- rings1 #fe ----1 ,selection of #ch ---- stoppers1 #ff ---- ,strong1 #ci1 #fd ----1 ,tempering1 #ci1 #fa ----1 ,weathering1 #ci1 #fa ,flint glass1 #d ---- stones1 #d ,fluorspar1 #h ,foot maker1 #hb ,formulas1 #ab1 #ba ,frisbie's ,feeder1 #dg ,furnaces1 #ba1 #da1 #ea1 #eg ,fusibility of glass1 #i ,gadget1 #bh ,garnet1 #ca ,gas-fired furnaces1 #dg1 #ea1 #ee ,gathering1 #gf1 #gg ,glass1 ,afterworkings of1 #hf ----1 ,alkalies in1 #bc ----1 ,alumina in1 #i1 #aa1 #bj ----1 ,ancient1 #b ----1 ,annealing1 #ga ----1 ,cane1 #ig ----1 ,coloured1 #bh ---- cloth1 #aja ----1 ,cut1 #aji ----1 ,enamelled1 #aae ----1 ,founding of1 #fi1 #gd ---- furnaces1 #ba1 #da1 #ea1 #ef ----1 ,gauge1 #ah ----1 ,grinding of1 #id ----1 ,hardened1 #ie ----1 ,homogeneity of1 #bc ---- house pots1 #fb ----1 ,moulds for1 #gg ----1 ,melting of1 #fi ----1 ,plasticity of hot1 #d-af ----1 ,polishing of1 #ib-id ----1 ,properties of1 #ae ----1 ,process of making1 #ae1 #gf ----1 ,sand-blasted1 #aad ----1 ,scum on1 #fi ----1 ,seeds in1 #aje ----1 ,silvered1 #aaf ---- snow1 #aja ----1 ,stress in1 #gd ----1 ,strengthened1 #ie ----1 ,temperature of melting1 #bj ----1 ,tube1 #if ----1 ,types of1 #ae1 #be ----1 ,wired1 #ie ---- wool1 #aja ----1 ,yellow1 #bh ,grinding tumblers1 #aaj ---- plate glass1 #ib1 #id ,hardened1 #ah1 #bc ,hermansen's ,furnace1 #eb1 #ec ,history1 #a ,homogeneity1 #bc ,honey pot making1 #he ,hydrofluoric acid1 #ai ,introduction of glassmaking in ,england1 #b ,iridescence1 #ba-aja ,iron in glass1 #cb ,italian ,aventurine1 #ajb ,laboratory glass1 #be ,ladling glass1 #de ,lamp glass chimneys1 #af ,lead glass1 #ba ---- poisoning1 #ad ,lehr1 #ga ,light and glass1 #cc ,lime glass1 #be1 #bf ,machines in glassmaking1 #gi1 #aaa ,mechanical boy1 #hf ,millefiore1 #ajj ,moulds1 #he ,opalescent glass1 #ie-aji ,opal glass1 #bi1 #ca ,optical glass1 #e1 #i1 #cc1 #ajd ,oxidising agents1 #g ,pearl ash1 #f ,pearls1 #ca1 #aaf ,phosphates in glass1 #h ,polariscope1 #gd ,potash1 #f ---- glass1 #bd ,pots1 #h-ac1 #bg-eh ----1 ,annealing1 #ff ---- cracking1 #de1 #fi ---- clays1 #cg1 #fd ----1 ,glazing1 #fi ----1 ,making1 #fb ----1 ,open1 #ba1 #bg1 #fd ----1 ,plumbago1 #fe ----1 rings1 stoppers1 #fc-fe1 #ff ---- sherds1 #fe ----1 ,setting1 #fg ----1 ,trolley1 #df ,plaining glass1 #d1 #ea1 #fi ,plasticity1 #aa1 #af ,plate glass1 #bf1 #ic ,plumbago1 #fe ,pressed glass1 #bf1 #gg ,pucellas1 #hb ,quartz glass1 #ai ,raumur's ,porcelain1 #ag ,recipes for glass making1 #be1 #bf ,recuperative furnaces1 #eb-ed ,reduction in glass1 #bh1 #ca ,regenerative furnaces1 #di ,rocaille flux1 #be ,roman glass1 #b ,ruby glass1 #bh1 #ca ,rupert drops1 #ah ,saltpetre1 #g ,sands1 #d ,sand-blast1 #aad ,scratching glass1 #af ,screens for pot setting1 #fh ,seeds in glass1 #d1 #ac1 #aje ,servitor1 #hc ,shearing glass1 #ha1 #hc ,sheet glass1 #ia ,siemens ,furnace1 #dh ,siege of furnace1 #dc1 #dd ,silica1 #d1 #e ,silicates in glass1 #bd ,silvering glass1 #aaf ,simple glasses1 #bd ,soda-lime glass1 #ba-bf ,soft glass1 #e ,soluble glass1 #bd ,spun glass1 #ae1 #ajj ,stirring glass1 #aje ,strengthened glass1 #ie ,stress in glass1 #ah1 #ajd ,striae1 #i ,sulphates1 #e1 #be ,table glass1 #be1 #gf1 #gg ,tank glass1 #bf1 #eg ,technical ,education in glass manufacture1 #abj ,temperature of furnaces1 #bj1 #aje ,thermal expansion of glass1 #af ,tin oxide in glass1 #aj ,tizeur1 #dc1 #df ,tools1 #gf ,topaz1 #ca ,trades ,unionism1 #hf ,tube1 #bf1 #ih ,tumblers1 #he1 #aaj ,turquoise1 #ca ,uranium1 #bh ,varieties of glass1 #be1 #ajb ,venetian glass1 #b ,violet glass1 #bh ,waste glass1 #cj ,waterglass1 #bd ,wine-glass making1 #hb ,window glass1 #a ,wired glass1 #ie ,working hours1 #abj ,zinc oxide1 #i ,printed by ,sir ,isaac ,pitman ,sons1 ,ltd41 ,bath1 ,england ---------------------------------------- -------------------------------- ,transcriber's ,notes3 ,missing or obscured punctuation was silently corrected4 ,typographical errors were silently corrected4 ,inconsistent spelling and hyphenation were made consistent only when a predominant form was found in this book4 ,text that was in italics is enclosed by underscores 7italics72 text that was bold by 8equal0 signs 7bold74 ,the use of a caret 77 before a letter1 or letters1 shows that the following letter or letters was intended to be a superscript1 as in ,st ,bartholomew or #ajth ,century4 ,superscripts are used to indicate numbers raised to a power4 ,in this plain text document1 they are represented by characters like this3 8,p#c0 or 8#ajah01 i4e4 ,p cubed or #aj to the #ahth power4 ,variables in formulae sometimes use subscripts1 which look like this3 8,a#j04 ,this would be read 8,a sub #j04