GEMS, ARTIFICIAL 



633 



Another. 

 White lead of Clichy, 771-6 ; flints calcined and pulverised, 771*6, 



Another. 



Oxide of silver . 

 Calcined potash 



White sand, well dressed 

 Borax, calcined . 

 Minium 



1543-23 

 138-88 

 2237-64 



. 77'16 

 .49376 



Sapphire: Whitest strass, 3858-086 ; pure oxide of cobalt, 57708. 



Ditto: another. Very fine strass, 481 '25; purest oxide of cobalt, 1*697. 

 Emerald, No. 1. Strass, 3858-087; pure green oxide of copper, 35-643; oxide of 

 chrome, 1-697. 



Ditto: ordinary. Strass, 7716-174; acetate of copper, Gl'll ; oxide of iron, 12-731. 



Ditto: another. Strass, 481-25; oxide of copper precipitated from the nitrate by 

 potash, 334-45. 



Emeralds (Bastenaire). 



Amethyst (Bastenaire). 



Aquamarine, 

 Strass, 2913-53 ; Glass of antimony, 20,370 ; Oxide of cobalt, 1-265. 



Syrian Garnet. 



Observations. For topaz, No. 1, the clearest and most transparent glass of antimony 

 should be used. Frequently this mixture only yields an opaque mass, translucent on 

 the edges, and transmitting in thin fragments a red colour when held between the 

 eye and the light : in that case rubies may be made of it. 



To make them, a portion of the topaz material is taken, and^mixed with eight parts 

 of fine strass : these are melted in a Hessian crucible for thirty hours in a potter's 

 furnace, and the result is a beautiful yellow glass-like strass, which, when cut, pro- 

 duces an imitation of the finest oriental rubies. 



These may be made of another tint by. using the following proportions : 



Strass, 2411-25; oxide of manganese, 61-310. 



In the emerald, No. 1, by increasing the proportion of chrome or oxide of copper, 



