GLASS 



early times simple vessels and 

 rough window glass were made in 

 the forests of Surrey and Sussex. 

 In the 14th century some, -at any 

 rate, of the glass required for 

 glazing the windows in S. Stephen's 

 Chapel, Westminster, came from 

 Chiddingfold in Surrey. The 

 Venetian adventurers of the 15th 

 and 16th centuries left few tradi- 

 tions. The members of the fami- 

 lies of Hennezel and Tyzack, from 

 Lorraine, who came over in 1576, 

 made England their home and had 

 a lasting influence. They moved 

 from place to place, wherever fuel 

 was available, and their names, 

 often mutilated, are to be found 

 in church registers in Sussex, Sur- 

 rey, Hampshire, Gloucestershire, 

 in Stourbridge, Newcastle, and 

 London. They introduced improved 

 methods of making window glass, 

 and new forms of drinking glass. 

 Development of the Industry 



The progress of the industry 

 can be traced in a long series of 

 special licences and monopolies. 

 Sir R. Mansell's monopoly lasted 

 from 1618 to 1653, and was con- 

 tingent on his substitution of coal 

 for wood fuel. In 1696 there were 

 88 glass-houses ; the excise list of 

 1833 gives 105 in England, 10 in 

 Scotland, and 10 in Ireland. By the 

 middle of the 18th century English 

 flint glass (sand-lead-potash) had 

 been perfected and used for cut 

 table-glass, the process of cutting 

 having been introduced from 

 Bohemia. The brilliancy of this 

 English glass eclipsed the German 

 crystal, and English cut glass 

 spread throughout Europe. The 

 best period was 1780 to 1810. The 

 chief centres were London, Stour- 

 bridge, Whittington, and Water- 

 ford, in Ireland. 



About the middle of the 18th cen- 

 tury taper-bowled wine glasses with 

 air twist in stem were introduced. 

 Few, if any, of the Jacobite glasses, 

 commemorating by engraved por- 

 traits, emblems, and mottoes the 

 risings of 1715 and 1745, belong 

 to the dates commemorated. The 

 Bristol milk glass of the end of the 

 18th century, enamelled by Michael 

 Edkins, has considerable merit. The 

 Nailsea rolling-pins and other 

 utensils, streaked or spotted with 

 enamel and colours, were merely 

 by-products of the great crown 

 glassworks (1793 to 1871) and have 

 no real technical or artistic value. 



Lighthouse and optical glasses, 

 the coloured glasses made for 

 stained -glass windows from analy- 

 ses of medieval specimens, and 

 vessels of simple and graceful 

 form due to the influence of Wil- 

 liam Morris, date from the latter 

 part of the 19th century. To the 

 U.S.A. may be attributed the in- 



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troduction of pressed table-glass, 

 Tiffany's lustrous vases, and a 

 great variety of automatic ma- 

 chinery which must destroy the 

 handicraft of glass-making. 



Glass is a non-crystalline, trans- 

 parent mixture of fused silicates. 

 The glasses known as " sheet " 

 and " plate " are mixtures of the 

 silicates of soda and lime, the in- 

 gredients being sand, carbonate of 

 lime, and sulphate or carbonate of 

 soda. Table or "flint " glass is 

 usually a mixture of the silicates or 

 potash and lead, the ingredients 

 being sand, red-lead, and carbonate 

 of potash. 



The temperature at which glass 

 mixtures melt ranges from about 

 1,200 C. to 1,500 C. When 

 thoroughly melted, glasses become 

 sufliciently liquid to be poured 

 Most, in cooling, pass from 

 liquidity to a stage of viscosity, re- 

 sembling the condition of stiff 

 treacle. In this state glass can be 

 coiled or " gathered " round the 

 end of a heated iron rod, as 

 treacle can be coiled round the 

 bowl of a spoon, and if the iron 

 rod be hollow (a blowpipe) the 

 lump can be blown out into a 

 hollow bulb. Viscous glass can be 

 squeezed and extended by an iron 

 roller, moulded by air pressure or 

 by a mechanical plunger, and, 

 owing to its ductility, can be 

 pulled or " drawn " out into an 

 almost invisible filament 



Glass is melted in tank-furnaces 

 or pot-furnaces heated by gas. 

 A glass-melting tank is an oblong 

 bath built of large blocks of fire- 

 clay, and covered with a low 

 arched " crown " of silica bricks. 

 The raw materials are put in at 

 one end, and worked out at the 

 other as molten glass. There are 

 two kinds of pots (crucibles), one 

 like an open basin, the other 

 shaped like an old-fashioned bee- 

 hive, with a hooded opening near 

 the top. 



Pot Furnaces 



Pot furnaces are circular, oval, 

 or oblong. They are covered with 

 a low crown supported on arches, 

 within which the pots stand Until 

 recently the fireclay for making 

 pots was prepared by mixing it 

 with water, and kneading it with 

 the bare feet. The pots were built 

 up of long rolls of clay, carefully 

 consolidated by hand pressure. 

 The clay is now prepared in a pug- 

 mill, and the pots formed in. 

 plaster of Paris moulds. 



Glass is a bad conductor of heat, 

 and if suddenly cooled is liable to 

 break, owing to internal tension. 

 Glassware must therefore be cooled 

 slowly (" annealed "). Glasses of 

 special composition are now made 

 for gas chimneys and cooking 



utensils, to resist extreme changes 

 of temperature ; the alteration of 

 the zero-point in thermometers is 

 counteracted by the use of stable 

 zinc-borosilicate glass, and other 

 glasses are made to resist the co- 

 rosive action of heat, steam, 

 alkalis, and acids. No glass, how- 

 ever, can withstand hydrofluoric 

 acid, which is used for etching and 

 for polishing glass. 



Colour Effects in Glass 



Effects of colour in glass are 

 due to ingredients melted with 

 those of the glass, and held in 

 oolution or suspension. The 

 colouring ingredient is usually a 

 metallic oxide, e.g. cobalt gives 

 a rich blue ; chromium a yellow- 

 green ; manganese a violet ; nickel 

 purple or brown ; ferrous oxide 

 dull green. 



MACHINE-JHADE GLASS. Much of 

 modern glass is now machine made, 

 and the development of automatic 

 machinery must be credited to the 

 U.S.A. The " Owens " bottle- 

 machine revolves, and has fifteen 

 or more arms successively making 

 bottles. An arm is thrust out, 

 sucks into a mould from a basin of 

 molten glass the exact quantity 

 required to make a bottle, forms 

 the neck by a plunger, and the body 

 in a second mould by compressed 

 air admitted through the neck. 

 It drops the finished bottle into a 

 shoot, which carries it to and 

 through an annealing kiln. Directly 

 one arm has obtained its glass, the 

 succeeding arm commences oper- 

 ations. 



The arms of a similar machine 

 used for tumblers and chimneys, 

 turn the glasses horizontally within 

 the moulds to obliterate mould 

 marks. When liberated from the 

 moulds, the tops of tumblers, and 

 both edges of chimneys, have to 

 be cut off and the edges melted. 

 The arms of the Westlake electric- 

 lamp machines, after blowing the 

 initial bulbs, elongate them by 

 swinging before blowing, and turn- 

 ing them in the moulds. 



The Colburn or Libby - Owen 

 sheet-glass machine lowers a 

 straight bar or " bait," previously 

 heated into a trough of molten 

 glass, and draws over a roller a 

 continuous sheet. The Frink 

 sheet-glass machine lowers an 

 annular bait into a basin of molten 

 glass, so that it encircles a vertical 

 air f ipe in the centre of the basin. 

 The bait when raised draws up a 

 continuous glass cylinder, which, 

 owing to air entering through the 

 pipe, retains its shape. The 

 cylinder is cut into lengths suitable 

 for flattening. In the Libby-Owen 

 tube making machinery molten 

 glass flows over a hollow mandril, 

 revolving horizontally. The glass 



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