Diamond Cutting: Forms

There are two principal forms into which diamonds are cut, the brilliant and the rose, both of them subordinate, in the first place, to the thickness of the stone. To each of these two types is attached a number of derivative and more simple forms.

THE BRILLIANT

The starting point for the modern diamond, as for the ancient Indian form, is the simple octahedron. The following is the method employed in forming the octahedron into a brilliant:--

In Fig. 103 let the line AB which joins the two opposite summits, be divided into six equal parts, and let a plane perpendicular to the line AB pass through the second division from the upper point, and another plane also at right angles to AB pass through the first division from the lower point, then a small pyramid will be detached from each extremity, and there will remain the solid represented by Fig. 104.

These are the proportions in which the axis is cut by the French lapidaries, but English lapidaries usually cut five-eighteenths from the upper pyramid, and one-eighteenth from the lower. The upper and larger plane surface is called the table; the lower is named the collet (French, culasse).

The four superior edges or ribs, and the four inferior edges, are then removed in such a way that the table and the collet are circumscribed by regular octagons, as represented by Fig. 105.

Lastly, the eight faces which limit the table are cut each into four facets, forming the crown; and the eight faces of the collet are divided in the same manner to obtain the pavilion.

The stone bears then sixty-four facets, besides the two parallel planes--the table and the collet. It is called the double-cut, or recut brilliant, and being the style which best displays all the beauties of the diamond, it is used at the present day for all stones of fine water and of sufficient depth. Figs. 106 and 107 represent this form as seen both vertically and horizontally.

The simple-cut brilliant has the same general form, but it has only eight facets above and eight below--sometimes only four--besides the table and collet.

There is another cutting for stones whose thickness is small in proportion to their surface. It is the semi-brilliant. It consists of the upper part of a double-cut brilliant, cut off at the line of junction between the crown and pavilion. This form is represented by Fig. 108.

THE ROSE

In rose-cutting, the diamond is flat underneath; the upper and convex part is covered with a variable number of facets, systematically disposed around a first, of which the summit occupies the centre of the stone. If the stone bears twenty-four facets it is a "Holland Rose;" if it has but eighteen or twenty, it is a "Semi-Holland;" if the number of facets is diminished to twelve, or eight, or even six, it is an "Antwerp Rose."

THE BRIOLETTE

Sometimes rough diamonds, found in the form of pears, are covered with little facets, retaining the general form. These stones have the name of briolettes; they come exclusively from India, and are generally pierced in the upper part with a very small hole. No lapidary in Europe could drill such a hole in these diamonds.

THE PENDELOQUE

There are also known in commerce stones cut into pendeloques or pendants, in the form of a half-pear with table and collet, covered with facets on the collet side. They are very rare, and their price far exceeds that of brilliants of the same weight. Fig. 110 represents one of the pendeloques which Tavernier saw in India, and which its possessor would not part with for $11,160.

Another special form of cutting is that which was employed for "the Sancy." Diamonds cut in this style have the form of flattened pears almost round, of a pendeloque shape, facetted both superiorly and inferiorly, and having a very small table above. M. Babinet thinks that this is the form in which both the Koh-i-noor and the Star of the South should have been cut.

THE STAR