gem, ornamental mineral or organic substance: Gem Cutting

Gems are generally cut to bring out their natural color and brilliancy and to remove flaws. In the cabochon cut, the upper surface of the stone is smoothed and rounded into a simple curve of any degree of convexity; the lower surface may be concave, convex, or flat. All the remaining cuts have flat facets. In the table cut, the facets of the natural octahedron of the diamond are ground to smoothness and polished; one facet, the table, is ground much larger than any other and made the top of the gem, while the opposite facet, the culet, is left quite small. The rose cut consists of a flat base and (usually) 24 triangular facets—resembling a cabochon with facets. The brilliant cut is scientifically designed to bring out the maximum brilliancy of the stone. The crown of a brilliant consists of a table and 32 smaller facets, of which 8 are quadrilaterals and 24 are triangles; the base, of a culet and 24 larger facets, of which 8 are quadrilaterals and 16 are triangles. The base and crown are separated by a girdle. The brilliant cut has certain proportions—in general, the depth of the crown is one third the depth of the stone and the width of the table one half the width of the stone. The trap, step, or emerald cut consists of a table and quadriangular facets above and below the girdle with parallel horizontal edges. Diamond cutting and the cutting of other precious stones are distinct trades.

Sections in this article:

• Introduction
• Counterfeit Gemstones
• Precious and Semiprecious Gemstones
• Other Gemstones
• Diamond Cutting
• Gem Cutting
• Properties of Gems
• Bibliography

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.

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