56 PRECIOUS STONES.
Garnets are frequently cut "en cabochon." In
this form the upper surface is a low dome, convex towards the eye ; the
under surface is flat, or, in the case of very intensely coloured
stones, concave, so that the stone in section would show a parallel
curved outline ; or the concavity may be such as to leave the stone
thicker at the centre and thinner at the edges. Rarely, the upper
convex surface is worked in small facets around its margin. Turquois is
often cut en cabochon, Chrysoprase may be cut so, too, but more often it is given a lower curve, " Goutte de suit" being the name then used.
Many
of the coloured gems as Topaz, Sapphire, Ruby, Emerald, Garnet,
Peridot, Amethyst, Cairngorm, etc., are frequently step-cut, though
they may be formed into brilÂliants, and are, in many cases, so cut.
The Chrysoberyl is usually cut as a brilliant; colourless Corundum is
usually step-cut; most of the opaque gems are cut either en cabochon or
as the " tallow-drops " above referred to ; very often the margin in
Chrysoprase is worked with one or two rows of small triangular facets.
Cat's-eye is usually cut en cabochon, and the finished stone
must be so arranged as to have a definite relation to the internal
structure of the gem, to show its full beauty. Moonstone and
Labradorite must also have a definite relation to the crystal structure
to bring out the best effect.
In
the actual cutting of precious stones in general, a careful study of
the rough stone has first to be made to determine in what direction it
can best be cut so as to leave as large a finished gem as possible,
free from imperÂfections; this having been decided on, these
imperfections are removed and the stone brought to approximately tbe
desired shape by methods varying with the mineral in
