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.
Reversing the stone and again commencing at the girdle, we have eight "skill facets," sometimes called the lower skill facets, the bases of which are on the girdle, their outer sides forming the bases of eight cross facets, the apexes of which meet on the extremities of the horizontal line, as in those above the girdle. If the basal lines of these cross facets, where they join the sides of the skill facets, are extended to the peak, or narrow end of the stone, these lines, together with the sides of the cross facets, will form four five-sided facets, called the "pavilions"; the spaces between these four pavilions have their ends nearest the girdle formed by the inner sides of the skill facets, and of these spaces, there will, of course, be four, which also are five-sided figures, and are called "quoins," so that there are eight five-sided facets—four large and four narrow—their bases forming a square, with a small portion of each corner cut away; the bases of the broader pavilions form the four sides, whilst the bases of the four narrower quoins cut off the corners of the square, and this flat portion, bounded by the eight bases, is called the "culet," but more commonly "collet." So that below the girdle, we find twenty-five facets: 8 cross, 8 skill, 4 pavilion, 4 quoin, and 1 collet.
These, with the 33 of the crown, make 58, which is the usual number of facets in a brilliant, though this varies with the character, quality, and size of the diamond. For instance, though this number is considered the best for normal stones, specially large ones often have more, otherwise there is danger of their appearing dull, and it requires a vast amount of skill and experience to decide upon the particular number and size of the facets that will best display the fire and brilliance of a large stone, for it is obvious that if, after months of cutting and polishing, it is found that a greater or smaller number of facets ought to have been allowed, the error cannot be retrieved without considerable loss, and probable ruin to the stone. In the case of the Cullinan diamonds, the two largest of which are called the Stars of Africa, 74 facets were cut in the largest portion, while in the next largest the experts decided to make 66, and, as already pointed out, these stones are, up to the present time, the most magnificent in fire, beauty and purity ever discovered.
The positions and angles of the facets, as well as the number, are of supreme importance, and diamond cutters—even though they have rules regulating these matters, according to the weight and size of the stone—must exercise the greatest care and exactitude, for their decision once made is practically unalterable.
CHAPTER XII.
IMITATIONS, AND SOME OF THE TESTS, OF PRECIOUS STONES.
We now arrive at the point where it is necessary to discuss the manufacture and re-formation of precious stones, and also to consider a few of the tests which may be applied to all stones. These are given here in order to save needless repetition; the tests which are specially applicable to individual stones will more properly be found under the description of the stone referred to, so that the present chapter will be devoted chiefly to generalities.
With regard to diamonds, the manufacture of these has not as yet been very successful. As will be seen on reference to Chapter II., on "the Origin of Precious Stones," it is generally admitted that these beautiful and valuable minerals are caused by chemically-charged water and occasionally, though not always, high temperature, but invariably beautified and brought to the condition in which they are obtained by the action of weight and pressure, extending unbroken through perhaps ages of time.