GLASS MANUFACTURE. 



GLASS MANUFACTURE. 



method of obtaining some such 8ect M this WM devised by Mr. 

 Johnson in 1853. It consists in hying piece of glass on another 

 piece of different colour ; softening and uniting them by the heat of 

 an enamel-furnace ; stomping a device on the upper surface by a die ; 

 and then grading away moe* of the upper glass by which the upper 

 colour prcMDts iUelf as a device let or incriuted in the lower. The 

 mcnuferf glass, or ary*aUo-c*ra*u, invented by Mr. PelUtt, consists in 

 forming a small medallion baa-relief, alto-relief, or other article, of a kind 

 of clay which baa the property of expanding and contracting by change* 

 of temperature just in the aame degree as flint-glass ; thin is imbedded 

 in a man of rol-hot glass ; and when cooled, annealed, fashioned, 

 ground, and polished, the glass appears with the device in the middle 

 of iu substance ; the clay, under these circumstances, presenting an 

 appearance almost exactly like that of unbumished silver. The owMsji 

 of flint-glass is effected by processes not differing much from that of 

 porcelain. [PORCELAIN MANUFACTURE.] Two or three patents have 

 bean taken out for tUctroyildmg on glass : but this process has not yet 

 come extensively into use. 



Artificial Gem*. Before passing to the consideration of other kinds 

 of glass, we may say a few words concerning the art of making imita- 

 tive gems and precious stones, which resemble flint-glass more than any 

 other substance. A transparent, fusible, dense glass, called paste or 

 ami, is the basis employed. To make good stress is the primary 

 work to be done. There are many recipes for producing it. One, by 

 Loyoel, consists in using pure silica, 100 parts ; red oxide of lead, 150 ; 

 calcined potash, SO ; calcined borax, 10 ; and arsenious acid, 10. This 

 mixture produces a glass of great brilliancy, much power of refracting 

 and dispersing -light (on which the flashing lustre of gems, whether 

 real or factitious, so much depends), and a specific gravity not far 

 different from that of the diamond ; it fuses at a moderate heat, and 

 acquires additional brilliancy when kept heated for two or three days. 

 Diamonds are imitated by this uncoloured stress ; and other gems by 

 mixing this stress with colouring agents. For every different factitious 

 gem, there are numerous combinations known ; but a few examples 

 will suffice to illustrate the general character of all. Amethyst : stress, 

 100 parts; oxide of manganese, 3; and oxide of cobalt, 2. AIJUM- 

 marine : stress, 4800 parts ; glass of antimony, 30 ; and oxide of 

 cobalt, 14. Avanturiiu: stress, 600 parts; scales of iron, 100; and 

 protoxide of copper, 50. Beryl : nearly the same as for aquamarine, 

 of which beryl is only a variety. Chrysolite : stress, 7000 parts ; and 

 calcined sesquioxide of iron, 65. Cornelian, or Cornelian; stress, 

 7000 parts; glass of antimony, 8500; calcined peroxide of iron, 875; 

 and binoxide of manganese, 75. Emerald : stress, 7000 parts ; car- 

 bonate of copper, 65 ; and glass of antimony, 7. Garnet : stress, 1200 

 parts ; glass of antimony, 580 ; purple of cassias, 3 ; and binoxide of 

 manganese, 3. Lapis lazuli : stress, 7000 parts ; calcined bones, 570 ; 

 oxide of cobalt, 24 ; and oxide of manganese, 24. The golden veins in 

 this beautiful stone are imitated by painting in the composition with a 

 mixture of gold-powder, borax, and gum-water, and then applying a 

 gentle heat till the borax fuses. Opal: strass, 960 parts; and cal- 

 cined bones, 48. Ruby : strass, 45 parts ; and binoxide of manganese, 

 1 ; or in another variety, 1 part of topaz paste, which has turned out 

 too opaque, with 8 of strass, fused together for thirty hours, cooled, and 

 fused again in small pieces before the blowpipe. Sapphire : strass, 

 3600 parts ; oxide of cobalt, 50 ; and oxide of manganese, 11. Topaz : 

 stress, 1050 parts; glass of antimony, 44; and purple of cassius, 1. 

 Tnrr/uoue : blue strass, 20 parts ; and calcined bones, 1. There is a 

 peculiar mode of producing imitative rubies and emeralds by the use 

 of a kind of alum-glass, subjected to a long and elaborate series of 

 processes ; and another, by M. Gaudin, for producing imitative sap- 

 phires by an equally elaborate treatment of alum and sulphate of 

 potash. There are other modes of imitating gems ; but we need not 



them here. 



Cram Glaa.Tha is one of two varieties of blown glass. It is 

 made without any admixture of metallic oxide, and is both specifically 

 lighter and much harder than flint-glass. Many receipts have been 

 given for the production of this kind of glass. At the great works of 

 St. Oobain, in France, the mixture of ingredients is said to be : fine 

 white sand, 100 parts; carbonate of lime, 12; carbonate of soda 

 calcined, 4S ; clippings of crown-glass, 100; with minute portions ol 

 nunginn** and cobalt to correct impurities, and to remove the 

 colour which those impurities would impart ; they are not therefore 

 at all times necessary. In England the ingredients are mostly sand, 

 alkali, and slaked lime, in the proportions of 200 of the first, 330 of the 

 second, and 15 of lime, to which is added about half the weight ol 

 the three materials in broken crown-glass, called by the makers cutlet. 

 The perfect fuxion and refining of these materials are usually accom 

 pushed in aU.ut forty hours. Crown-glass is made by blowing, in tli< 

 form of circular plates ol 54 to 70 inches diameter. A quantity of 

 glass in the pasty state is collected upon the end of a hollow iron tube 

 five feet long, similar to the tube used for blowing flint-glass. The 

 lump of glass is then converted, by blowing through the tube, into a 

 hollow globe of the requisite substance. This globe is flattened at the 

 nde opposite to the tube by pressing it upon a hard plane surface ; 

 a solid rod of iron having a small quantity of melted glass at the 

 end is applied, and adheres to the centre of tho flattened side opposite 

 to the tub*; the tub* is finally removed by watting the glass near 

 the point of union, leaving a small circular hole. To arrive at this 



stage the 'glass must have been several times re-heated, by placing 

 t, when connected with the tube, within a small opening left for 

 .he purpose in tho wall of the furnace. When transferred from the 

 tube to the solid rod, called a ptmtil, it must be again heated in 

 the same manner, and is then twirled round by the workman some- 

 what in the manner that a mop is twirled to drive off the moisture ; 

 with this twirling the softened material is continually driven off from 

 :he centre by the centrifugal force ; the hole just mentioned expands, 

 from a few inches to a foot or more in diameter, when suddenly, 

 and in a most unaccountable manner, it flies open, and the whole 

 substance is converted into a flat disc of circular form, and. except 



Flashing-out Crown-g!a.. 



at the centre, where it is attached to the rod, of a uniform thickness. 

 This flathmg of the glass as it is called, is one of the most striking and 

 surprising things in the whole manufacture. The centre parts are 

 used for the commonest purposes, such as glazing outhouses and the 

 poorer kinds of windows. As the shape of the tables or pieces of glass 

 is circular, and as there is a bulb or bull's eye in the middle, it is 

 impossible to obtain very large panes of crown-glass ; and the differ- 

 ences of quality are so great and so uncertain, that the best are worth 

 thrice as much per square foot as the worst. Nevertheless, there is 

 always a brilliancy of surface upon crown-glass, which renders it 

 valuable. 



Sheet Giant. This is another kind of blown-glass, which has become 

 a very important article of manufacture in England within the last 

 twenty years. Before that time, glass of a peculiar kind was imported, 

 under the names of broad, spread, or German ikeet-glatl ; but the 

 sheet-glass of modern make is a French invention, and French work- 



Swinging ind blowing- Shttt-glnM. 



men are largely employed in its manufacture, even in English esta- 

 Mi-lmii-nta. It required six years, 1832 to 1338, for Messrs. Chance and 

 other manufacturers to overcome the numerous difficulties which beset 



