Gems in the Smithsonian InstitutionDesautels, Paul E.
History
Gems in the Smithsonian Institution
Desautels, Paul E.
Gems; Precious stones; Smithsonian Institution
For other purposes and for other kinds of precious stones a number of
basic cuts have been developed. The _brilliant_ and _step_ cuts are by
far the commonest of these basic cuts, but modern jewelry design
frequently uses such fancy cuts as the baguette, cut-corner triangle,
epaulet, half moon, hexagon, keystone, kite, lozenge, marquise,
pentagon, square, trapeze, and triangle. Some of these are shown here.
[Illustration: Just as the English brilliant cut, because of its 28
fewer facets, has less sparkle than the standard brilliant cut, the
step brilliant, with its 20 additional facets, has greater sparkle.]
[Illustration: The step brilliant cut is a complicated modification
of the standard brilliant. With an additional 12 facets in the crown
and 8 in the pavilion, the step brilliant has 78 facets, compared
with the 58 of the standard.]
[Illustration: Various kinds of cuts have been devised for special
purposes in jewelry design. These include the pentagon (1), lozenge
(2), hexagon (3), cut-corner triangle (4), kite (5), keystone (6),
epaulet (7), baguette (8), trapeze (9) and square (10).]
[Illustration: With this typical trim saw, water is used as a
coolant for the rapidly rotating metal disk, which has a
diamond-impregnated rim. Here, the blade is cutting its way through
a piece of gem tourmaline.]
In general, there are three operations in preparing a gemstone from the
rough—sawing, grinding, and polishing. Sawing usually is accomplished by
using a thin, diamond-impregnated, rapidly rotating disk of soft iron or
bronze, with oil or water being used as a coolant. The very hard diamond
dust literally scratches its way through the stone. Once the stone is
sawed to shape, the facets are ground and polished on a rotating
horizontal disk by the use of various abrasives. For rough grinding,
silicon carbide—or sometimes diamond powder—is used. Scratches are
removed and a high polish is given by the use of tin oxide, pumice,
rouge, or other fine-grained abrasives. The thick disks, or laps, are
made of cast iron, copper, lead, pewter, wood, cloth, leather, and
certain other materials. Since each species of gemstone differs in its
characteristics, each must be treated somewhat differently as to sawing
and lapping speeds, kind of lap, and choice of abrasives. Because of the
greatly increased interest in gem cutting as a hobby and the large
number of amateur cutters, a substantial market has developed in the
United States for lapidary supplies and equipment. New kinds of
machinery, new abrasives, and new kinds of saws and laps are introduced
regularly. Fundamentally, however, the process still involves sawing,
grinding, and polishing.
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