Artificial Gems. These consist of vitreous compounds made in imitation of gems and precious stones. Like enamels, the artificial gems have for their basis a very fusible, highly transparent and brilliant dense glass, which is known under the name of frit, paste, strass, mayence base, etc., and which, in its state of greatest excellence, consitutes the artificial diamond. As the strass or base enters largely into the manufacture of imitation gems, we give the method for making it first. It is absolutely necessary, to ensure success in the following receipts, that the substances employed be perfectly free from impurities, particularly those of a mineral nature. Litharge, oxide of lead, and carbonate of lead especially, must be entirely free from oxide of tin, as the smallest particle of this imparts milkiness to the paste. All the ingredients must be separately reduced to powder; and, after being mixed, sifted through lawn. For the finer kinds of mock diamonds, rock crystal should alone be employed; when sand is used, the purest white variety should be selected, and be washed thoroughly, first with muriatic acid and then with water, to remove any traces of earthy matter. Much of the minute detail in making artificial gems can only be acquired by experience. The fusion must be carefully conducted and continuous, and the melted mass allowed to cool very slowly, after having been left in the fire for 24 to 30 hours at least. Hessian crucibles are preferred for this purpose, and the heat of an ordinary porce-lain kiln is usually sufficient; but a small wind-furnace, devoted exclusively to the purpose, is in general more convenient. It is found that the more tranquil, continuous and uniform the fusion, the denser and clearer is the paste, and the greater its refractive power and beauty. All the colored vitreous compounds noticed as enamels (see No. 2378, etc..) may be worked up in this way into ornamental stones. It may be further observed that the beauty of pastes or imitation gems, and especially the brilliancy of mock diamonds, is greatly dependent on the cutting, setting up, and the skillful arrangement of the foil or tinsel behind them. (See Enamels, No. 2378, fa.; Foils, No. 2447, etc..)

2420. Diamond Paste, or Strass

2420.      Diamond Paste, or Strass. Litharge, 20 parts; silica, 12 parts; nitre and borax, each 4 parts; white arsenic, 2 parts; powder mix, fuse in a crucible, pour the melted mass into water, separate any reduced lead, and again powder and re-melt.

2421. Mayence Base, or Strass

2421.    Mayence Base, or Strass. Silica (quartz, flint or rock crystal;, 8 ounces; salt of tartar, 24 ounces; mix, bake, pool, wash with dilute nitric acid, and afterwards with water; dry, powder, add 12 ounces pure carbonate of lead, and to every 12 ounces of the mixture add borax, 1 ounce; triturate in a porcelain mortar, melt in a clean crucible, and pour the fused compound into cold water; dry, powder, and repeat the process a second and a third time in a clean crucible, observing to separate any revived lead. To the third frit add nitre, 5 drachms, and again melt. Very brilliant. Or: Carbonate of lead, 8 ounces; powdered borax, 2 ounces; rock crystal, 3 ounces; manganese, 1/2 grain; mix, and proceed as last.