The chemistry, properties and tests of precious stones — John Shaqi
The chemistry, properties and tests of precious stonesMastin, John
Science
The chemistry, properties and tests of precious stones
Mastin, John
Precious stones
The most common of all, and usually applied only to the diamond, is the
"brilliant" cut. This is somewhat complicated, and requires detailed
description. In section, the shape is substantially that of a pegtop
with a flat "table" top and a small flat base. The widest portion is
that on which the claws, or other form of setting, hold it securely in
position. This portion is called the "girdle," and if we take this as a
defining line, that portion which appears above the setting of this
girdle, is called the "crown"; the portion below the girdle is called
the "culasse," or less commonly the "pavilion." Commencing with the
girdle upwards, we have eight "cross facets" in four pairs, a pair on
each side; each pair having their apexes together, meeting on the four
extremities of two lines drawn laterally at right angles through the
stone. It will, therefore, be seen that one side of each triangle
coincides with the girdle, and as their bases do not meet, these spaces
are occupied by eight small triangles, called "skill facets," each of
which has, as its base, the girdle, and the outer of its sides coincides
with the base of the adjoining "cross facet." The two inner sides of
each pair of skill facets form the half of a diamond or lozenge-shaped
facet, called a "quoin," of which there are four. The inner or upper
half of each of these four quoins forms the bases of two triangles, one
at each side, making eight in all, which are called "star facets," and
the inner lines of these eight star facets form the boundary of the top
of the stone, called the "table." The inner lines also of the star
facets immediately below the table and those of the cross facets
immediately above the girdle form four "templets," or "bezils." We thus
have above the girdle, thirty-three facets: 8 cross, 8 skill, 4 quoin, 8
star, 1 table, and 4 templets.
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