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opalescent
as in moonstone and asterism as in 'star' stones. Stones that depend
mainly on their colour or markings are cut in this way, e.g. garnets.
The dark garnet requires a hollow cabochon cut to give a pleasing
colour or, due to its thickness, it will appear very dark.
Faceted cutting
The
art of cutting smooth plane surfaces of geometrical design and symmetry
on gems has been credited to Louis de Berquem of Bruges, Belgium. The
discovery was made about 1456 or 1476, but it is also considered that
it was known and practised earlier in Italy and France. 'According to
Henri Polak, a Venetian craftsman, Vincenzo Peruzzi was probably the
first to cut the diamond in the shape now known as the " brilliant".'
FORMS OF CUT STONES
The
'rose cut' was then developed and used in diamond cutting. It is not
much used now except in the case of small stones. It has a flat base,
with triangular facets to the number of 12 or 24 or 32, which terminate
at a point, and are grouped about the upper part of the stone. The
outline of the stones may be circular, elliptical or oval. In some
cases a double rose cut is given an upper and a lower portion. (See
Fig. 37.)
The
'brilliant' cut, introduced about the end of the seventeenth century,
has been extensively used for the diamond, since it brings out to
marked advantage the remarkable fire and brilliancy of the gem. The
octahedron is the basis of this cut. The upper and lower parts of a
natural octahedron crystal are smoothed off and polished. The upper
face is known as the 'table'—much wider than the lower facet known as
the 'culet'. 3/8 of the height is removed from the upper part and 3/16
from the ldwer part.
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