Prof. Royle’s Lecture on the Great Exhibition of 1851. 167 : 
difficult to find materials pure enough to make good glass, and it 
would be some time before the original makers would find out 
the causes of discoloration. 
The natives of India seem to have been long acquainted with 
making different ornaments of glass: for instance, armlets and 
anklets, while rings of glass form a part of their warping reels. 
Small glass bettles are also made; but all that I have seen are of 
amore or less greenish color. The green is called kanch, and 
the purer glass, sisi. It is probable that the extensive diffusion 
of oxyd of iron in the Indian soil, which may have led to the 
discovery of iron, has prevented the making both of good glass 
and of good pottery. That this is not incompatible with a 
knowledge of the method of making imitation gems, seems 
proved by the same having been the case in the time of Pliny; 
who states that great value was set upon glass quite free from 
color, which was called crystal. He also mentions artificial hya- 
cinths, sapphires, and all kinds of black glass; and we know 
that the glass-houses of Alexandria were celebrated among the 
ancients. 
Make blackish and greenish glass: a bright grass-green is made 
by additions of oxyd of copper; and a blue glass by the ot 
Chester gallons. About fifty of these crucibles are placed in a 
furnace, and the fire kept up for five days, when a frit 18 pro-. 
— with which they make a black, green, red, blue, and yok 
