204 A Book of Precious Stones
tions
similar to the American brilliant, but with a greater height from the
girdle to the centre of the table, caused by the facets replacing the
table being carried to a low pyramidal point in the centre.
Subsequently the style was modified, the stone being cut thinner and
with but eighty facets, the central top facets being almost flat. This
cut is helpful in some cases, especially to shallow stones, but it
probably exceeds the limit of efficiency in the effort to increase the
surface reflection and dispersion of light rays, and experience has not
demonstrated its success.
The
cabochon cuts represent different degrees of convexity above the
girdle, and beneath a concave, plane, or slightly convex surface. The
double cabochon is customarily cut with a smaller curvature on the base
than on the crown. The single cabochon is a characteristic cut for the
turquoise. The hollow cabochon is best for deep-coloured transparent
stones. The mixed cabochon has either the edge or side, or both,
faceted. The degree of convexity in the various cabochon cuts is made
to depend upon the nature of the stone to which the cut is to be
applied. The cabochon cuts are specifically within the province of the
lapidary.
