Diamond Cutting

DIAMOND CUTTING On account of its extreme hardness, the treatment of the diamond in preparation for use in jewellery 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, there fore, (I) 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.

I. Cleaving or Dividing.—Diamonds are always found as crystals, usually octahedral in form, though often irregular or dis torted. The problem involved in each case is twofold: (I) to ob tain 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. 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.

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 cleav ing 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 di vided 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 English carats. The stone was taken to Amster dam to be treated by the old-fashioned hand method, with innu merable precautions of every kind at every step, and the cutting was successfully accomplished after nine months' work (see The Times, Nov. I°, 1908). (See DIAMOND.) 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, which is now generally employed in Antwerp.

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 ma chine method, invented about 1885 and first used by Field and Morse of Boston, is now used at Antwerp exclusively.

At Amsterdam a hand-process is employed, which lies between the cleavage and the brutage. This consists in cutting or trim ming 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.

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 pro duced. This is the work of the cutter; it is very laborious, and re quires 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 adjustable 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 2,500 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 symmetry.

The rapid development of mechanical and electrical devices for the several stages of diamond cutting has already greatly in fluenced the art. (G. F. K.)