A stone cabochon cut is cut in a smooth upward (convex) curve, like the arc of a circle or an ellipse. Most frequent is the medium cut, a smooth oval with the under surface flat. The steep cut produces a dome-like effect, as of a small haystack or high mound. In the hollow cut, the upper surface is convex and the lower surface is concave, the effect being that of a small bar curving upward. The fourth commonly used cabochon cut is the double cut, the upper surface curving up and the lower surface curving down, like a tiny elongated football. Which of these cuts is used depends partly upon the jewel for which the stone is intended, but mainly upon the original shape and coloring of the stone.
Facets
Transparent and translucent stones which seem to have radiance are usually made more beautiful by faceting. A facet is a small, smooth face or plane surface; a number of these are cut upon a gem.
In most facet-cut gems five regions can be distinguished. The table—the top of the stone—is usually flat, though it may be slightly domed; it is usually the largest of the facets, though the size may vary according to the stone and the type of cut. The bezel is the slope from the top, consisting of slanted, smooth faces that may proceed in various planes or by ninety-degree “steps” down to the girdle. The girdle is the widest part, the “equator,” of the cut stone; it is here that the setting is usually attached. The pavilion is the part that slants down from the girdle to the culet, which is the bottom point of the stone. Sometimes the stone is slightly truncate; that is, it is cut to a small flat surface, instead of a point, at the culet. More generally, the part of the stone above the girdle is the crown; the part below the base.
Types of Faceting
There are many patterns of faceting. Six are fairly common.
1. Brilliant. This is used especially for large diamonds, which are then often called brilliants. The gem is cut as though two pyramids with sixteen-sided bases were placed base against base, the points at opposite ends. The upper point is truncated, to form the table. Brilliant-cut gems usually have 58 facets, 33 above the girdle, 25 below. For the sake of the superb light effects achieved by this cut, there is often sacrificed a considerable portion of the original stone.
2. Rose. This may be used for smaller diamonds and other gems. The rose cut is circular, with the table slightly domed. It is flat underneath. The part above the girdle is usually cut into 24 equal facets.
3. Square. This cut, as its name indicates, provides a square table. The facets are cut parallel to the girdle, both above it and below. Since they will thus seem to be proceeding downward in a succession of steps, this is also called the step cut.
4. Emerald. The emerald cut may have either a square or an oblong table. The corners, instead of being pointed and at right angles as in the square cut, are cut off and faceted. As the name implies, this is a frequent cut for the emerald, but the topaz, amethyst, aquamarine, and other stones—even the diamond—may be square cut or emerald cut.