The chief forms of cutting used are the brilliant cut, the step (or trap) cut, the mixed cut, the rose cut, and various forms of cabochon cuttings. Transparent stones are usually faceted; opaque and translucent stones are generally cut en cabochon. There are a number of other so-called “fancy” cuts, these being usually seen with diamonds, topaz, amethysts, aquamarines, and a few other stones.
The brilliant cut is so called because it is characteristic of the diamond. The number of the facets, their inclination to each other, and the ratio of the width to the depth of the stone are factors which have been definitely established by practice and calculation, and any departure from the acknowledged standards will lessen the brilliant effect which is such an outstanding property of this gem. If properly cut, there will be 57 facets (or 58 if a culet is present), and the brilliancy of the finished stone will depend largely upon the proportion of these facets to each other.
The girdle divides the upper part, or the crown, from the base, and it is usually circular. It is the only part of the finished stone which is generally left unpolished. If the girdle is not circular, the arrangement of the facets will be distorted. It should be as
thin as is practical but not so thin that there would be a risk of chipping when the stone is set in a mount. In order to obtain the maximum brilliancy and fire, light falling on the table (which is the broad, flat, large facet on the top of the stone) should be refracted and then reflected from the base facets, ultimately emerging from the crown facets. Additional facets are sometimes used in large stones, and their inclination might be modified to suit the optical characteristics of the particular specimen.
Of the 57 facets, 33 are contained in the crown. There is the large facet on the top surface, called the table, which is octagon shaped; 8 triangular star facets, 8 quadrilateral facets (4 templets and 4 quoins, sometimes called bezel and top main facets, or top corner facets), and 16 triangular facets (8 cross and 8 skill facets, sometimes called top half or break facets).