46 ROCK CRYSTAL, 
Its uses are numerous. It is cut into vases, lustres, 
and snuff-boxes ; and many kinds of toys of extremely 
beautiful appearance are made of it. When pure and 
perfectly transparent, it is much in request by opticians, 
who make of it those glasses for spectacles which are 
called pebbles, and who use it for various kinds of op- 
tical instruments. The best crystal is imported from 
Brazil and Madagascar, in blocks, not urifrequently 
from fifty to a hundred pounds in weight. 
This stone is wrought into the different shapes that 
are required, by sawing, splitting, and grinding. The 
sawing is effected by an extended copper wire fixed to 
a bow : the wire is coated with a mixture of oil and 
emery, and is drawn backward and forward until the 
operation is performed. But, as this process is a 
tedious one, particularly when the mass is large, a more 
expeditious, although less certain, method is sometimes 
adopted. The crystal is heated red hot, and a wet 
cord is drawn across, in the direction that the workman 
intends to split it. By the rapid cooling thus effected, in 
the direction of the cord, the stone easily splits by a sin- 
gle blow of the hammer, and generally in the direction 
required. The grinding is performed by means of emery : 
and the polishing effected by tin ashes and tripoli. 
The ancients held vases that were made of this stone 
in great estimation, particularly when they were of 
large size. Of two cups which the tyrant Nero broke 
into pieces in a fit of despair, when informed of the 
revolt that caused his destruction, one was estimated to 
be worth more than 600/. of our money. The most valu- 
able kind of crystal that was known to the ancients was 
obtained from the island of Cyprus ; but it was often 
faulty in particular parts, having flaws, cracks, and 
blemishes. When the crystal was used for the engrav- 
ing of intaglios and cameos, the artist could sometimes 
conceal these defects amongst the strokes of his work ; 
but, when it was to be formed into cups or vases, this 
could not be done, and for the latter purpose the purest 
pieces only could be employed. 
