GEMS

Gem Cutting

The forms just described may be regarded as typical brilliant forms, and are used far more frequently than any other. They are nevertheless subject to certain modifications, not, however, deviating far from the normal types. These modifications usually take the form of variations in the arrangement and number of the facets; in the latter case further small facets are introduced in groups, which are placed symmetrically relative to the other facets. The majority of the large historical diamonds are cut in the brilliant form, as an examination of Plate 4 and Plate 5 will show. On comparing these forms with the normal forms of Plate 1 a strong general resemblance, accompanied by differences in minor details, will be noticed.

To bring out all the beauties of a stone, and to display them to the greatest possible advantage, involves infinite care and precision in the cutting. The facets must be regularly and symmetrically grouped, and corresponding facets must be of precisely the same size; moreover, it is of the greatest importance that all the different parts of the stone should be correctly proportioned. In this connection may be mentioned the following rules which are generally observed, and which are only departed from where there are special reasons for so doing.

The height of the upper portion of the brilliant above the girdle must be one-third, and that of the lower portion must be two-thirds, of the total thickness of the stone from table to culet. The diameters of the table and culet must be respectively five-ninths and one-ninth of the diameter of the girdle; hence the diameter of the table is five times that of the culet. Few of the best cut and most beautiful brilliants show any essential deviation from these dimensions; the exceptional cases mentioned above occur when the rough stone is of such a shape that to give it these proportions would involve too great a waste of material; or, again, in the case of a coloured stone, where the thickness is varied in order to obtain the particular depth of colour desired.

The "Koh-i-noor", the famous diamond now in the English crown jewels (Plates 4, Fig. 5), on account of the former reason departs considerably from the typical form. The "Regent", a large brilliant in the French crown jewels, is perhaps the most perfectly beautiful stone of its kind existing at the present day (Plate 5, Fig. 8). It conforms with the greatest precision to the proportions laid down above, and consequently far surpasses the "Koh-i-noor" in brilliancy and play of colours, although the two stones are equal in quality. It remains to be mentioned that the girdle of a brilliant is sometimes left with sharp edges (Plates 4, Fig. 5), as is the custom of English gem-cutters; or the edges may be ground down (Plate 5, Figs. 8 and 9), as is done in Holland. The former plan improves the appearance and effect of the stone, but the sharp edges are liable to get chipped, which is not the case when they have been rounded off.

Mention may be made here of the half-brilliant (or brillonette), which is very occasionally made use of. It is essentially an ordinary brilliant, the under portion of which is replaced by a single large face, which forms a base to the upper portion as in rosettes. This device is occasionally resorted to when the rough stone is very flat, but the appearance of a stone so cut is far inferior to that of a complete brilliant.

Parisian jeweller, Caire, at the beginning of the nineteenth century, devised the star-cut, which is closely related to the brilliant form and is illustrated in Plate 2, Fig. 1 a, b, c. In this form Caire aimed at combining the advantages of the brilliant with those of the rosette, as may be seen from the diagrams, the facets are arranged in multiples of six, and are distributed with great regularity, which serves to enhance the appearance of the stone. This form of cutting was devised principally for diamond, to which it gives a very effective star-like or rayed appearance, very little inferior to that of the ordinary brilliant. The cutting of this form from the majority of rough stones is attended with but little loss of material; the form is, however, not in general use.

2. Step-cut or trap-cut-The different types of step-cut stones, together with the various modifications of this form, are illustrated in Plate 2, Figs. 2 to 8, and Figs. 2 to 4 being typical forms. In one of these (Fig. 2 b) the girdle is square; in another hexagonal (Fig. 3 b); in a third it is eight-sided (Fig. 4 b, c), while it may be occasionally twelve-sided. The outline of the girdle may be such that all its diameters are approximately equal, or it may be more elongated in one direction. Above the girdle rises the upper portion of the stone, bearing a large table of the same outline as the girdle (Figs. 2 b, 3 b, 4 b); the lower portion terminates in a small culet (Figs. 2 a, 4 c), or in a point (Figs. 7 a, c). On both portions lie a series of facets arranged in such a way that their edges of intersection are parallel to the corresponding edges of the girdle. In passing from the girdle to the table or to the culet, the facets become successively less and less steeply inclined (Fig. 2 a, etc.). The upper portion has two, or sometimes three, series of facets, each series differing but slightly in their inclination to the table. The facets of different series may be of the same width (Figs. 2 b, 3 b), or the facets of the lower series are wider than those of the uppermost bordering on the table (Fig. 4 b). On the lower portion of step-cut stones, there are usually from four (Figs. 8 a, c) to five series (Figs. 2 a, 4 c, etc.) of facets. None of the facets of these lower series differ in width.

The step-cut is the form employed for less deeply coloured stones, which are not cut as brilliants. It brings out the colour and lustre of the stone to greater advantage; it must, however, be specially proportioned, particularly in the lower portion, to suit the stone to which it is applied. The brilliancy and colour of the stone do not attain their full value with an insufficient number of facets; there are scarcely ever less than four or five series of facets on the lower portion of the stone, and in faintly coloured stones this number may be increased. In such faintly coloured stones the lower portion is rather deep, as is shown in the figures, while in stones of a deep colour it is flat, sometimes very flat. While certain insignificant modifications of the lower portion of step-cut forms are effective in varying the depth of colour of the stone, the upper portion may undergo more marked modifications, a few of which are illustrated in Plate 2, Figs. 5 to 8. Here we find the step-like facets of the upper portion replaced by an arrangement of facets similar to that of a brilliant. These forms are therefore, to a certain extent, combinations of the step-cut and the brilliant-cut, and are in general specially suited to stones of a pale colour. The mixed-cut (Fig. 5 a, b) is a form in frequent use; it bears on the upper portion a series of triangular star facets and of similarly shaped cross facets, separated by a series of four sided facets. The mixed-cut brings out in light-coloured stones a stronger brilliancy and lustre than does the typical step-cut. The outline of the girdle in this form need not necessarily be circular, as in Fig. 5, but may be square, hexagonal, etc..

Fig. 6 a, b, shows the cut with double facets, a form which differs from the mixed-cut in that several single facets of the latter are replaced by two facets; the arrangement of these facets in two series can be easily made out tram the diagrams without further explanation. The cut with double facets is no more effective than is the mixed-cut; it is used simply for the purpose of removing, or rendering inconspicuous, any faults, which may exist in the rough stone. In the cut with elongated brilliant facets the arrangement of the facets on the upper portion is much the same as in the previous form; the facets, however, are much elongated or shortened (Fig. 7 a, b, c). The outline of the girdle may approach that of a square, as in the girdle, or it may be oblong. This form of cutting is peculiarly adapted to stones of an elongated shape, and it brings out their lustre to a marked degree; the elongated brilliant facets seem to compensate for any lack of depth in the lower portion of the stone. Another similar form is that known as the Maltese cross (Fig. 8 a, b, c), so called from the cruciform arrangement of its facets. Other similar forms exist, differing but slightly from those already described; a detailed account of these is therefore unnecessary.

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Large and Famous Diamond Properties Diamond Geology and Mining Diamond Cutting Diamond trade

Rafal Swiecki, geological engineer email contact
January, 2008

This document is in the public domain.