The object of cutting and polishing the Diamond is twofold. First, to divide the natural surface of the stone in a symmetrical manner, by means of a number of highly polished polygonal planes, and thus to bring out to the best advantage, the wonderful refulgence of this beautiful gem ; and secondly, by cutting out such flaws as may happen to be near the surface, to remove those blemishes that materially detract from its beauty, and consequently from its value.
The removal of flaws is a matter of great importance, for, owing to the form in which the Diamond is cut, and its high degree of refrangibility, the smallest fault is magnified and becomes obtrusively visible in every facet. For this reason also, it is by no means an easy matter, at all times, to ascertain whether a flaw is, or is not superficial; and a person with a correct and well-practised eye, may often purchase to great advantage stones which appear to be flawed quite through, but are in fact only superficially blemished.
The first thing that the artist has to do when a rough Diamond is put into his hands, is to examine carefully, in what direction the stone may be cut, so as to afford the greatest breadth, or spread as it is technically termed, after the flaws, if any, shall have been taken out. So great a stress is laid by modern fashion, on the superficial extent of a brilliant, that the old rules for proportioning its dimensions are now nearly obsolete: the best cutters have entirely discarded the use of measures, and in forming the facets, trust wholly to an accurate and well-practised eye.
The direction being determined on, the artist must be well aware which are the hard points, and which the soft ones; the former being those solid angles of the original octohedron, which it is necessary to cut directly across, and the latter, those solid angles which are to be obliquely divided.
A degree of force which may be safely applied, and is even requisite in making a section through the former, will be very apt to flaw and tear up the laminae when applied to the latter. On these accounts it probably is, that the fatiguing and even painful process of performing this part of the business by hand, is not yet superseded by the use of machinery.
These preliminary matters being settled, the Diamond is imbedded in strong cement, fixed at the end of a stout spindleshaped-stick about a foot long with that portion only projecting, the removal of which is to form the first facet.
The instrument employed for this purpose is another Diamond fixed in a stick similar to the former, with one of the solid angles projecting. In order to collect the powder and shivers that are detached during the process, the cutting is performed over a strong box four or five inches square, furnished with a false bottom perforated with excessively minute holes, in order to sift, as it were, the dust from the shivers; and also with two upright iron pegs fixed on the sides, for the workman to support and steady his fingers against, while with a short repeated stroke somewhat between scratching and cutting, he is splitting off or more laboriously wearing away the Diamond in that part where the facet is to be placed.
This being done, the cement is softened by warming it, and the position of the Diamond is changed, in order to bring a fresh part under the action of the cutting Diamond. When in this slow and laborious way all the facets have been placed upon the surface of the Diamond, the cutting is completed. The stone, if examined by a moderate magnifier, now presents ragged rough edges; and a broken foliated surface with a glistening lustre on those facets that are nearly in the direction of the natural laminae, and on the other facets a more even surface, but of a dull opake greyish white colour.
The shape of many Diamonds is so irregular, that it is necessary to remove pieces of considerable magnitude, in order to bring them to a form proper for cutting. Where the lines of these proposed sections coincide with the natural lamellar structure of the stone, the workman has recourse to the delicate and perhaps somewhat hazardous operation of splitting the Diamond, by which a double advantage is obtained. In the first place there is a great saving of time, and in the second place the slices of shivers are themselves sufficiently large to admit of being cut and polished. The method of splitting is made a great mystery of, thus much however may be mentioned, that when the direction in which the section is to be made has been determined on, it is marked by a very fine line cut by the point of another Diamond; the stone is afterwards fixed by strong cement in the proper position in a block of wood, and then by the application of a due degree of force the section is effected.
The Diamond being thus, by the joint action of splitting and cutting, brought to the required form, the next object is to polish the facets, and at the same time to redress any little inequalities that may have taken place in the cutting.
