whose
breadth to its depth is too much extended, and which would not, without
much loss, make a good brilliant. There are fragment rose-diamonds,
which are very small, and ear-drop roses.
C. The Table-Diamond is
that stone which is very flat and of little depth, and which reflects
but little lnstre. They have a table with four planes and eight facets,
and, in order to make the best of their lustre, they receive a
brilliant cut.
D. The Bastard-Diamond is that diamond whose cut is mixed up from the above forms.
There are a few more
forms given to those diamonds which are found unfit for any of the
above cuts, such as the thick-stones, the portrait-diamonds, the
senail-diamonds, which are, however, all unfit for the above cuts.
FORMS OF GEMS.
The gem lapidary occupies himself not only with grinding the common and rare gems, but also pastes, &c He
uses likewise wheels, but of different material from those
for-diamonds. His wheels are either of copper, if for very hard stones,
or of lead or pewter for softer stones; he has likewise polishing
wheels. If a wheel is too soft for very hard stones, he cuts furrows in
it, which are then filled out with rotten-stone or tin-ashes; or if
very hard stones, such as sapphire, .are to be ground, the diamond
powder is used for the same. Tin wheels are used for hard stones; water,
or oil of vitriol, is used for moistening the wheels. The gems (in
order to grind them or to give their facets) are cemented into a
handle, at the end of which is a composition of resin and brickdust.
Particular attention is required in grinding the colored, gems, as the
greatest effect may be produced by their "thickness; pale-colored gems
require to be left thicker -than darker ones; on the
