Part 235

Artificial borax is given the preference, since the native variety frequently contains substances which color the glass. Lead carbonate or red lead must be perfectly pure and not contain any protoxide, since the latter gives the glass a dull, greenish hue. White lead and red lead have to dissolve completely in dilute nitric acid or without leaving a residue; the solution, neutralized as much as possible, must not be reddened by prussiate of potash. In the former case tin is present, in the latter copper. Arsenious acid and saltpeter must be perfectly pure; they serve for the destruction of the organic substances. The materials, without the coloring oxide, furnish the starting quantity for the production of artificial gems; such glass pastes are named “strass.”

The emerald, a precious stone of green color, is imitated by melting 1,000 parts of strass and 8 parts of chromic oxide. Artificial emeralds are also obtained with cupric acid and ferric oxides, consisting of 43.84 parts of rock crystal; 21.92 parts of dry sodium carbonate; 7.2 parts of calcined and powdered borax; 7.2 parts of red lead; 3.65 parts of saltpeter; 1.21 parts of red ferric oxide, and 0.6 parts of green copper carbonate.

Agates are imitated by allowing fragments of variously colored pastes to flow together, and stirring during the deliquation.

The amethyst is imitated by mixing 300 parts of a glass frit with 0.6 parts of gray manganese ore, or from 300 parts of frit containing 0.8 per cent of manganic oxide, 36.5 parts of saltpeter, 15 parts of borax, and 15 parts of minium (red lead). A handsome amethyst is obtained by melting together 1,000 parts of strass, 8 parts of manganese oxide, 5 parts of cobalt oxide, and 2 parts of gold purple.

Latterly, attempts have also been made to produce very hard glasses for imitation stones from alumina and borax with the requisite coloring agents.

Besides imitation stones there are also produced opaque glass pastes bearing the name of the stones they resemble, e. g., aventurine, azure-stone (lapis lazuli), chrysoprase, turquoise, obsidian, etc. For these, especially pure materials, as belonging to the most important ingredients of glassy bodies, are used, and certain quantities of red lead and borax are also added.

GEM CEMENTS: See Adhesives, under Jewelers’ Cements.

GERMAN SILVER: See Alloys.

GERMAN SILVER SOLDERS: See Solders.

GILDING: See Paints, Plating, and Varnishes.

GILDING GLASS: See Glass.

GILDING, TO CLEAN: See Cleaning Preparations and Methods.

GILDING, RENOVATION OF: See Cleaning Compounds.

GILDING SUBSTITUTE: See Plating.

GILT, TEST FOR: See Gold.

GILT WORK, TO BURNISH: See Gold. {371}

GINGERADE: See Beverages.

GINGER ALE AND GINGER BEER: See Beverages.

GINGER CORDIAL: See Wines and Liquors.

GINGER EXTRACTS: See Essences and Extracts.

«Glass»

«Bent Glass.»—This was formerly used for show cases; its use in store fronts is becoming more and more familiar, large plates being bent for this purpose. It is much used in the construction of dwellings, in windows, or rounded corners, and in towers; in coach fronts and in rounded front china closets. Either plain glass or beveled glass may be bent, and to any curve.

The number of molds required in a glass-bending establishment is large.

The bending is done in a kiln. Glass melts at 2,300° F.; the heat employed in bending is 1,800° F. No pyrometer would stand long in that heat, so the heat of the kiln is judged from the color of the flame and other indications. Smaller pieces of glass are put into the molds in the kilns with forks made for the purpose. The great molds used for bending large sheets of glass are mounted on cars, that may be rolled in and out of kilns. The glass is laid upon the top of the mold or cavity, and is bent by its own weight. As it is softened by the heat it sinks into the mold and so is bent. It may take an hour or two to bend the glass, which is then left in the kiln from 24 to 36 hours to anneal and cool. Glass of any kind or size is put into the kilns in its finished state; the great heat to which it is subjected does not disturb the polished surface. Despite every precaution more or less glass is broken in bending. Bent glass costs about 50 per cent more than the flat.

The use of bent glass is increasing, and there are 4 or 5 glass-bending establishments in the United States, of which one is in the East.

«Colored Glass.»—R. Zsigmondy has made some interesting experiments in coloring glass with metallic sulphides, such as molybdenite, and sulphides of antimony, copper, bismuth, and nickel. Tests made with batches of 20 to 40 pounds and with a heat not too great, give good results as follows:

Sand, 65 parts; potash, 15 parts; soda, 5 parts; lime, 9 parts; molybdenite, 3 parts; sulphide of sodium, 2 parts, gave a dark reddish-brown glass. In thinner layers this glass appeared light brownish yellow. Flashed with opal, it became a smutty black brown.

Sand, 50 parts; potash, 15 parts; soda, 5 parts; lime, 9 parts; molybdenite, 1 part; sulphide of sodium, 2 parts, gave a yellow glass.