CARBORUNDUM.
31
charged
with various grinding and polishing powders, are employed for different
stones, and in different stages of the operations. The wheel, or disc,
or lap as it is called, is usually horizontal and is made to revolve
with great rapidity. The grinding or polishing powder, mixed, according
to its nature, with olive oil or water, becomes partially embedded in
the lap. This powder, in the case of diamonds, must be of diamond
itself, generally in the form of boart, a dark and rather porous
variety of the mineral. The comparatively new and artificial compound
of silicon and carbon known as carborundum is now largely used in the
case cf the harder stones, but emery, garnet-powder, tripolite, rotten
stone, jeweller's rouge, pumice, putty-powder, and bole are in constant
requisition for the grinding and polishing of stones less hard than the
diamond. The whole subject of this mechanical treatment of stones,
including splitting, dividing and shaping operations, is one which
cannot be discussed here, involving as it does a large number of minute
technical details of no interest from an artistic standpoint.
