CULTURED PEARLS

Most of us are familiar with cultured pearls for they have been a part of almost every jeweler's stock since just before the war years of 1939 and onwards. To the uninitiated, they look very much like natural pearls, but to those who are accustomed to handling the natural gem, there is seldom any doubt as to their true origin. If doubt does exist, proof positive is readily obtain­able by the use of the endoscope or other instruments. Examina-tion by radiography allows a large number of specimens to be examined quickly, but the X-ray diffraction method is the best.

The production of the cultured pearl is based on the knowledge of the causes which produce the natural pearl, the best conditions under which it is formed, and the habits of the oysters. We have already seen that a pearl is formed by the accidental introduction of an irritant against the soft body of the oyster, and this irritant is covered by layers of pearl material by the oyster in its attempt to expel or isolate it. In cultured pearls, the irritant is artificially supplied, but the layers around this nucleus are the same as in natural pearls, although the skin is only one-tenth or less of the total diameter of the specimen.

This idea is not so recent as may be imagined. The Chinese have, for centuries, introduced enameled and metal figures of Buddha into the valves of the mollusc and so obtained small pearl-covered charms. They attribute the idea to a native of Hou-Tcheou-Fou, who lived in the Thirteenth Century. But they had never considered the production of round, necklace pearls on a commercial basis. This was left to the Japanese, although various previous attempts in this direction had been made.

Linnaeus, who was aware of the origin of pearls, was also able to produce them artificially. He suggested bringing together a number of mussels, piercing holes in their shells to produce wounds, and then leaving the oysters for five or six years to allow the pearl to form. The Swedish Government tried this experi­ment in secret, and pearls were produced, but as they were of little commercial value, the project was abandoned. Attempts of a similar nature carried out on the Australian coasts some fifty years ago also failed.

The making and marketing of cultured pearls in recent years is largely due to the work of the Japanese scientist Mikimoto. In 1894, he produced half pearls, and in 1913 the whole pearl. The half, and three-quarter, pearl is really a blister pearl. An artificial irritant is inserted between the mantle and the shell, usually a small mother-of-pearl bead, and this stimulates the deposition of nacre round the bead, just as would an accidentally introduced irritant.

The blister pearl so produced is cut from the shell and "backed" by a suitably shaped piece of mother-of-pearl. This back is generally cemented or pegged. A round bead is also made in this manner on occasions, but the joint between the backing and the pearl will be always seen. Such pearls are frequently mounted as button earrings, in rings and studs, since the setting will hide the mother-of-pearl back.

It was not until 1921 that the whole cultured pearl was marketed in quantity. The first pearls were of a slightly greenish tinge, which characterizes the natural pearl found in Japanese waters, and for this reason their nature was not suspected. But today, all shades are produced, and coloring matter is even some­times introduced to make the finished pearl of a rosee tint. The cheaper qualities are whitish and dull, and appear to have little nacre covering the mother-of-pearl bead. The better qualities are round, of a desirable shade, and the coating is of appreciable thickness. But by far the greater proportion of these pearls is nothing more than a mother-of-pearl bead.