PRECIOUS STONES. 53
rubbed
together. To Peruzzi would seem to belong the honour of discovering the
principle of modifying the back of the stone so as to bring out the
full brilliance of the specimen. As pointed out when dealing with
light, this brilliance depends jointly on refraction and repeated
internal reflection.
By
far the most important type of cutting is that called the brilliant. In
this form the greatest circumference of the stone is called the "girdle";
the portion lying above the girdle is the "crown," and that below is
the "culasse." The crown terminates in a large plane called the table
(a, Fig.7). Meeting the table in an edge are eight triangular facets
called the "star facets" (b, Fig. 7); meeling the girdle in an
edge are sixteen upper " skill facets " (c, Fig. 7); and between the
star facets and the upper skill facets are eight lozenge-shaped facets
known as " bezils " (d, Fig. 7). Below the girdle, that is on
the culasse, are sixteen triangular facets meeting the girdle in an
edge. These are the lower "skill facets" (f, Fig. 7); and
running from them to the lowest portion of the stone are eight facets,
with five sides each, called the " pavilions " (g, Fig. 7). The lowest portion of the stone is a small plane called the " collet " (h, Fig.
7). Sometimes the upper and lower skill facets are collectively
referred to as " cross facets." There are thus thirty-three planes in
the crown, and twenty-five in the culasse. The table and collet are
both parallel to the plane of the girdle.
There
is a general proportion in the finished stone which has become by the
experience of generations of cutters to be regarded as a standard,
because a stone so proportioned is found to give the greatest
brilliancy. Thus if the
