In various parts of the world certain dubious methods have been used for restoring the beauty of pearls which have grown dim. In India they are rubbed in boiled rice. Some persons have even fed them to a chicken fastened in a coop; after the lapse of an hour or two the chicken is killed, and the pearls rescued from their temporary lodging-place, where they have been somewhat restored by the digestive juices of the fowl.
Some curious tests applied to pearls are given us in a Hindu treatise on gems by Buddhabhatta. For instance, we read: “If the purchaser conceives a doubt as to the genuineness of a pearl, let him place it during one night in a mixture of water and oil with salt, and heat it. Or let him wrap it in a dry cloth and rub it with grains of rice; if it do not become discolored, it should be regarded as genuine.”[[416]] It is needless to state that these tests would be either useless or injurious.
If the reader is the owner of a pearl or of a pearl necklace and feels that the pearls need treatment, any attempt to follow the directions given by many ancient writers would infallibly result in their injury or destruction.
Pearl drilling is a most delicate operation. It is necessary that the drill points should have the proper shape,—that is, should not be too tapering, but slightly blunt at the end, and turning somewhat in a V-shape,—it is also important that the drill should be revolved with perfect regularity, so as not to jar or jolt the pearl, as this is likely to lead to the cracking of the pearl or to the breaking of the drill. This latter happens not infrequently, and is due either to the structure of the pearl, the clogging of the drill, or to encountering a hard grain of sand inclosed in the pearl. Should the drill break in the pearl, it can best be removed by drilling from a point directly opposite, and slowly forcing the broken drill outward. This process requires great care in the regulation of the speed, and great exactness of direction in order to meet the broken drill accurately.
Pearl drilling was formerly a laborious process, and it was scarcely possible for a driller to perforate more than from forty to fifty pearls per day by means of the bow-drill operated by hand. Now, by the use of a modern machine, 1500 pearls of average size can be drilled without any difficulty in the same time.
Some of the most successful drilling of fine pearls is done by means of the bow- or fiddle-drill. The arm of this is made either of steel or of wood, with a strong cord stretched across it in the style of an archer’s bow. The drill is inserted in the end of a brass circular disk with a V-shaped groove on its edge, to admit of the string being passed entirely around it like a pulley, so that when the drill is placed on anything and held at the other side, and the bow is moved up and down, the wheel with the drill-end rotates rapidly.
If the pearl is not properly secured, if the drill point is too irregular, if it is not properly centered, or if it is too rapidly rotated at the start, one or more layers of the pearl are likely to be broken, giving an irregular, ragged appearance. If, again, the drill is rotated too rapidly as it is leaving the other side of the pearl, one or more layers are occasionally forced off, and this in turn will produce a break on the pearl. It happens not infrequently that pearls are broken away on the surfaces at both drill holes if the workman is careless.
As pearls have become more valuable, only the most efficient workmen are employed in drilling them. Whereas formerly a drill hole would be half a millimeter in diameter, at present it is much smaller, and such drilling requires the greatest skill in manipulation. The use of these very fine drill holes is due principally to the fact that pearls have become so valuable that the slightest loss, even the fraction of a grain, would amount to a considerable sum in a necklace of large pearls.
When a pearl has been perforated with a very fine drill hole, the hole may be enlarged somewhat by using a slender copper wire, the fineness of the drill hole itself, charged with either diamond-dust, emery, or sand. When the wire thus charged is drawn in and out, the drill hole can be enlarged to any desired size.
A large pearl is held in the hand or secured in a wooden block, or else it is held in a small pair of forceps with a rounded, cup-shaped receptacle at the end, which is usually lined with chamois leather and is pierced with a hole through the center. This hole serves as a guide for the drill, directing it while the pearl is being perforated. Adjustable cups or forceps with cup-like ends of every size are necessary, according to the size of the pearl; and in order that it may be properly seen, it is requisite that the pearl should always be larger than the cup in which it is placed.