Emerald, a genus of precious stones belonging to the order of siliceous earths. This is perhaps the most beautiful of all the gems : when heated in fire, it changes its colours to a deep blue, and becomes phosphorescent ; it resumes its natural green on growing cold.
Emeralds are divided by jewellers into two classes or kinds, namely, the oriental and the occidental. The former is at present extremely scarce, being found only in the kingdom of Cambay, in India. The occidental emeralds are chiefly imported from Peru, in South America. A very inferior sort is also obtained from Silesia, which, however, is little esteemed.
Genuine emeralds being seldom to be met with, several experiments have been made, and directions given for imitating them ; from which we select the following : Take of natural crystal and of red lead, each 4 ounces; ver-digrease 48 grains ; and of crocus martis, prepared with vinegar, 8 grains. The whole is to be finely pulverized, sifted, and put into a crucible, the space of one inch being left empty. It is then to be well luted, set in a potter's furnace, and left for the same space of time as earthen ware. When cool, the crucible is to be broken, and these ingredients will be found converted into a mass of a fine emerald colour ; which, after being properly cut and set in gold, will at least be equal, if not superior, to genuine oriental emeralds.