within a recent period. Articles are made there, not only for all the
civilized world, but for exportation to half-civilized and even
barbarous nations, in great variety of shapes, styles and colours.
Diamond Cutting.—On account of its extreme hardness, the treatment of the diamond in preparation for use in jewelry constitutes a separate and special branch of the lapidary’s art. Any valuable gem must first be trimmed, cleaved or sawed into suitable shape and size, then cut into the desired form, and finally polished upon the faces which have been cut. The stages in diamond working are, therefore, (1) cleavage or division; (2) cutting; (3) polishing; but in point of fact there are four processes, as the setting of the stone for cutting is a somewhat distinct branch, and the workers are classed in four groups—cleavers, setters, cutters and polishers.
1. Cleaving or Dividing.—Diamonds are always found as crystals, usually octahedral in form, though often irregular or distorted. The problem involved in each case is twofold: (1) to obtain the largest perfect stone possible, and (2) to remove any portions containing flaws or defects. These ends are generally met by cleaving the crystal, i.e. causing it to split along certain natural planes of structural weakness, which are parallel with the faces of the octahedron. This process requires the utmost judgment, care and skill on the part of the operator, as any error would cause great loss of valuable material; hence expert cleavers command very high wages. The stone is first examined closely, to determine the directions of the cleavage planes, which are recognizable only by an expert. The cleaver then cuts a narrow notch at the place selected, with another diamond having a sharp point; a rather dull iron or steel edge is then laid on this line, and a smart blow struck upon it. If all has been skilfully done, the diamond divides at once in the direction desired. De Boot in 1609 mentions knowing some one who could part a diamond like mica or talc. In this process, each of the diamonds is fixed in cement on the end of a stick or handle, so that they can be held firmly while one is applied to the other.
When the stone is large and very valuable, the cleaving is a most critical process. Wollaston in 1790 made many favourable transactions by buying very poor-looking flawed stones and cleaving off the good parts. In the case of the immense Excelsior diamond of 971 carats, which was divided at Amsterdam in 1904, and made into ten splendid stones, the most elaborate study extending over two months was given to the work beforehand, and many models were made of the very irregular stone and divided in different ways to determine those most advantageous. This process was in 1908 applied to the most remarkable piece of work of the kind ever undertaken—the cutting of the gigantic Cullinan diamond of 302534 English carats. The stone was taken to Amsterdam to be treated by the old-fashioned hand method, with innumerable precautions of every kind at every step, and the cutting was successfully accomplished after nine months’ work (see The Times, Nov. 10, 1908). The two principal stones obtained (see Diamond), one a pendeloque or drop brilliant, and the other a square brilliant, were given 72 and 64 facets respectively (exclusive of the table and cullet) instead of the normal 56.
This process of cleavage is the old-established one, still used to a large extent, especially at Amsterdam. But a different method has recently been introduced, that of sawing,[1] which is now generally employed in Antwerp. The stone is placed in a small metal receptacle which is filled with melted aluminium; thus embedded securely, with only the part to be cut exposed, it is pressed firmly against the edge of a metallic disk or thin wheel, 4 or 5 in. in diameter, made of copper, iron or phosphor bronze, which is charged with diamond dust and oil, and made to revolve with great velocity. This machine was announced as an American invention, but the form now principally employed at Antwerp was invented by a Belgian diamond cutter in the United States, and is similar to slitting wheels used by gem cutters for centuries. Two patents were taken out, however, by different parties, with some distinctions of method. The process is much slower than hand-cleavage, but greatly diminishes the loss of material involved. It is claimed that not only can flaws or defective portions be thus easily taken off, but that any well-formed crystal of the usual octahedral shape (known in the trade as “six-point”) can be divided in half very perfectly at the “girdle,” making two stones, in each of which the sawed face can be used with advantage to form the “table” of a brilliant. By another method the stone is sawed at a tangent with the octahedron, and then each half into three pieces; for this Wood method a total saving of 5% is claimed. Occasionally the finest material is only a small spot in a large mass of impure material, and this is taken out by most skilful cleaving.
After the cleaving or sawing, however, the diamond is rarely yet in a form for cutting the facets, and requires considerable shaping. This rough “blocking-out” of the final form it is to assume, by removing irregularities and making it symmetrical, is called “brutage.” Well-shaped and flawless crystals, indeed may not require to be cleaved, and then the brutage is the first process. Here again, the old hand methods are beginning to give place to mechanism. In either case two diamonds are taken, each fixed in cement on the end of a handle or support, and are rubbed one against the other until the irregularities are ground away and the general shape desired is attained. The old method was to do this by hand—an extremely tedious and laborious process. The machine method, invented about 1885 and first used by Field and Morse of Boston, is now used at Antwerp exclusively. In this, one diamond is fixed at the centre of a rotating apparatus, and the other, on an arm or handle, is placed so as to press steadily against the other stone at the proper angle. The rotating diamond thus becomes rounded and smoothed; the other one is then put in its place at the centre and their mutual action reversed.
At Amsterdam a hand-process is employed, which lies between the cleavage and the brutage. This consists in cutting or trimming away angles and irregularities all over the stone by means of a sharp-edged or pointed diamond, both being mounted in cement on pear-shaped handles for firm holding. This work is largely done by women. In all these processes the dust and fragments are caught and carefully saved.
2. Cutting and Setting.—The next process is that of cutting the facets; but an intervening step is the fixing or “setting” of the stone for that purpose. This is done by embedding it in a fusible alloy, melting at 440° Fahr., in a little cup-shaped depression on the end of a handle, the whole being called a “dop.” Only the portion to be ground off is left exposed; and two such mounted diamonds are then rubbed against each other until a face is produced. This is the work of the cutter; it is very laborious, and requires great care and skill. The hands must be protected with leather gloves. The powder produced is carefully saved, as in the former processes, for use in the final polishing. When one face has been produced, the alloy is softened by heating, and the stone re-set for grinding another surface; and as this process is necessary for every face cut, it must be repeated many times for each stone. An improved dop has lately been devised in which the diamond is held by a system of claws so that all this heating and resetting can, it is claimed, be obviated, and the cutting completed with only two changes.
3. Polishing.—The faces having thus been cut, the last stage is the polishing. This is done upon horizontal iron wheels called “skaifs,” made to rotate up to 2500 revolutions per minute. The diamond-powder saved in the former operations, and also made by crushing very inferior diamonds, here comes into use as the only material for polishing. It is applied with oil, and the stones are fixed in a “dop” in much the same way as in the cutting process. Again, the utmost skill and watchfulness are necessary, as the angles of the faces must be mathematically exact, in order to yield the best effects by refraction and reflection of light, and their sizes must be accurately regulated to preserve the symmetry of the stone. In this process, also,
- ↑ The Universal Magazine of Knowledge and Pleasure for 1749 states that diamond dust, “well ground and diluted with water and vinegar, is used in the sawing of diamonds, which is done with an iron or brass wire, as fine as a hair.”—Ed.
