GLASS in a mould, around the inner sides of which are arranged pieces of canes of the required colors, as described in the case of filigree glass, which, adhering to the glass, form ribs or flutes on its external surface. The lump, having been twist- ed to give the spiral arrangement to the ad- hering canes, is formed into a conical shape and opened at the base. This forms the inner case of the vitro di trino. A corresponding outer case is formed in the same manner, which being turned inside out, the projecting canes appear on the inside of the cup with a reversed spiral arrangement. One case is now placed within the other, and both being reheated are collapsed together, forming uniform air bubbles between each white enamel-crossed section. The two cases, thus welded into one, may be formed into the bowl of a wine glass or other vessel. Frosted glass, like the preceding, is one of the few specimens of Venetian work not made by the ancients ; and although the process of making it is exceedingly simple, it was con- sidered a lost art until recently practised at the Falcon glass works in England. The appear- ance of irregularly veined, marble-like pro- jecting dislocations, with intervening fissures, is produced by immersing the hot glass in cold water, quickly withdrawing it, reheating the ball of glass, and simultaneously expanding it by blowing. Cameo incrustation is also of FIG. 17. Cameo Incrustation. modern origin, having been first introduced by the Bohemians. The figure intended for incrustation must be made of materials requi- ring a higher degree of heat for their fusion than the glass to be used. The figure, having been heated, is introduced into a cylindrical- shaped piece of glass, attached at one end to a blowpipe and open at the other. The open end is then closed, leaving the figure in the interior of the hollow pocket. The air is now exhausted through the hollow tube, which pro- duces a collapse and causes the glass and figure to form into a homogeneous mass. In making " paper weights," thin sections of little orna- mented rods are placed in a circular iron mould or bed, in the form of the required de- sign. A workman presses a piece of hot glass on the end of a punty into the mould and takes up the design. Then another workman drops a piece of hot glass on the opposite side of the design. The whole is now taken to the fur- nace, where the parts are welded into a hemi- spherical form, which magnifies the interior de- sign and presents a fine picture enclosed within the transparent setting. In making spun glass, the workman heats one end of a tube of glass, white or colored, by the flame of a lamp, and seizing the softened end with a pair of pincers draws out a long thread. Owing to the extreme ductility of glass, these threads can be drawn to an extraordinary fineness and length. In some cases spun glass has been made to imitate the hair of animals. Among the most valuable treatises on the subject of glass are " Curiosities of Glass Making," by Apsley Pellatt (London, 1849), and Guide du verrier, by G. Bontemps (Paris, 1868), both of these authors having been for many years extensively engaged in the manufacture of glass. Among other works are those of Neri, "The Art of Glass" (trans- lated, London, 1662); Shaw, " The Chemistry of Porcelain, Glass, and Pottery" (London, 1837) ; Henry Chance, " On the Manufacture of Crown and Sheet Glass" (London, 1856), and "On the Manufacture of Glass" (1868); Peligot, I? Art de la verrerie (Paris, 1862); Turgan, Les grandes mines de Prance (Paris, 1862-'70) ; Cochin, La manufacture des glaces de Saint- Gobain de 1665 a 1865 (Paris, 1865) ; Gaflield, "Action of Sunlight on Glass," re- printed from the " American Journal of Sci- ence and Arts " (New Haven, 1867) ; Sauzay, La verrerie (Paris, 1868), and " Wonders of Glass Making in all Ages " (London and New York, 1870) ; and Rapports du jury interna- tional of the Paris universal exposition of 1867, vol. cxi. (Paris, 1868). GLASS, Soluble, or Water Glass, an artificial sili- cate of soda or potash, or a double silicate of both these alkalies. It may be formed by fusing 8 or 10 parts of dry carbonate of soda or pot- ash with 15 parts of white sand or powdered quartz or flint. Nearly all glass is to a slight extent soluble in water, in consequence of the alkaline matter it contains ; and the solubility is increased by raising the temperature of the water, which under pressure may be carried far above the boiling point. Water holding caustic alkalies in solution will attack glass vessels containing it in consequence of the for- mation of a soluble alkaline silicate. It is to this quality of solubility that feldspar ordina- rily owes its value as a fertilizing ingredient of the soil ; and it is from the affinity of caustic lime for silica that it may be used for libera- ting the alkali in the feldspar. Attention was first directed to soluble glass by Fuchs as a suitable composition for rendering combustible bodies fire-proof; and in 1824 portions of the new theatre in Munich were coated with it. He also employed it in the style of fresco paint-
