that
when one Diamond is rubbed on another each is abraded ; it is made use
of to still more nearly approximate the stone to its desired form. The
stone is cemented to the end of a wooden holder about a foot long, and
two stones are wrought simultaneously by grasping the two holders and
rubbing the stones together in the desired direction over a wooden
trough, into which the fragments and dust fall, and in which they are
separated into larger and smaller particles by a fine sieve. In
bruting, care must be taken not to overheat the stone by the friction,
or a scaly appearance may be produced in the interior of the gem. When
the bruting is completed the surfaces have somewhat the aspect of
ground glass. The table and collet are the most important faces to be
dealt with at this stage, and entail the greatest amount of work, as
there is no cleavage that can assist in roughing out these planes ;
working in a plane normal to an axis of the octahedron five-ninths of
the upper pyramid must be removed to produce the finished table, and at
the other end of the same axis one-ninth of the lower pyramid for the
collet.
In
Amsterdam the Diamonds are sometimes slit by a disc of thin metal
revolving at high speed, and dressed on its edge by diamond-dust and
olive oil. This method allows of a slice being taken off in any
direction desired, but the process is extremely slow, taking many days
to accomplish; and it is stated that the resulting finished stone is
inferior in quality to one that has been cleaved.
Sometimes the larger planes are roughed out by working the stone in a high-speed lathe.
When the bruting is completed, there yet remains much work to be done, for the smaller facets have to be wrought
