GEMS, IMITATION, or Pastes, Plows Precieuses Artifeielles, French imitations of the precious stones, are made of glass specially prepared. It differs from ordinary glass in its greater density; at the same time it is made with the greatest possible amount of transparency and purity. Its composition, generally, may be said to be silica of very pure quality, probably quartz crystals, potash, and oxide of lead ; but the exact portions are varied almost by every maker, and each has a secret ingredient or two to add.
The colors employed are usually the same as those used for coloring ordinary orna mental glass, but upon their careful admixture, and upon the skilful cutting to repre sent the crystalline form of the real gem, the success of the manufacture chiefly depends. By some persons, the cutting is carried to such a marvelous perfection, that their work would deceive the eye of most ordinary judges, when well set and foiled, or backed with silver or tinfoil. See FoIL.
The glass used for artificial gems is very generally called stress, from the name of a German who claimed the invention. But if we seek the real inventor of factitious gems, we must go far beyond the time of Strass, for we fiud Pliny describing., under the name of gannue vitrece, certain imitations of precious stones which were kaown in his time, some of which were certainly made of colored glass, and others by ingeniously cementing together layers of variously colored transparent stones. And Seneca (Epist. ix.) mentions that one Democritus had invented a process for imitating emeralds by giving a green color to rock-crystal. Other allusions arc plentifully scattered through the works of classical authors; and ancient artificial gems themselves exist, two espec ially famous being imitations of a chrysolite and an emerald, amongst the Roman antiquities in the Museum Victorium at Rome.
The manufacture of factitious gems is chiefly carried on in Switzerland, and like the polishing of diamonds in Holland, is engrossed by a small community in the French commune of Septmoncel, on the .Jura Alps, 16 miles from Geneva. Upwards of a hunched artisans are there employed in this manufacture, and they make almost enough to supply the whole world. comnion coldied glass is cutup Iu this country for the purpose of making the gilt-toy jewelery, but the writer believes that a small manufacturer of the name of Weston, in Birmingham, is the only person who attempts fine imitations of precious stones with colored strass. The followim• are a few known formulas for imi
tating gems: Amethyst—Strass, 500 paits; oxide of manganese., 3 parts; and oxide of cobalt, 2 parts.. Diamond—Perfectly pure rock-crystal, '1600 parts; biborate of soda. 560 parts; very pure carbonate of lead, 3,200 parts; oxide of manganese, I part. A glass, consisting only of the oxide of tin, fused, is used for the so-called Parisian dia monds; they are the nearest in brilliancy to the real gem when newly made, but they soon lose their brilliancy. Etnerald—Strass, 7,000 parts; carbonate of copper, 65 parts; glass of antimony, 7 parts. Garnet, Oriental—Strass, 1200 parts; glass of antimony, 580 parts; purple of Cassius, 3 parts; binoxide of manganese, 3 parts. Ruby—Strass, 45 parts; bin'oxide of manganese, 1 part. Sapphire—Strass, 3,600 parts; oxide of cobalt, 50 parts; oxide of manganese, 11 parts. Topuz—Strass, 1050 parts; glass of antimony, 44 parts; purple of Cassius, I part.
Antz7ope Ory.r, or Oryx Gazelles, a species of antelope, described by some naturalists as the oryx, but which. being a native of South Africa only, cannot be the oryx (q.v.) of the ancients, although it is certainly a nearly allied species. It is a heavy, stout animal, about the size of a stag, with rough, reversed hair on the neck and along the ridge of the back; large pointed ears; and almost perfectly straight horns, fully 2 ft. in the plane of the forehead, little diverging, and obscurely ringed at the base. The colors are harshly contrasted, dark rusty gray above, and white on the under parts, separated by a broad dark brown or black band; the head white, with black transverse bands; the thighs black, and the legs white. The hoofs are remarkably long, adapted to the rocky, mountainous districts which the animal frequents. The gems-bok makes use of its horns as sometimes even to beat off the lion. It inhabits districts free from wood, and is generally found in pairs or in very small herds.