CULTURED PEARLS PRODUCTION

While Japan was at war, and for some years afterwards, produc­tion of cultured pearls was almost at a standstill. In 1939, the industry was in full swing, and then cultivation was being carried on in at least eight localities in Japan, as well as in the island of Palao. The farms employed about 2,500 workers over a period of six months, May to October. Round beads were drilled and strung on the small island of Toba, where 250 workers were em­ployed. Of the 200 necklaces strung daily, only some 20 were exported in strung bunches of approximately the same qualities, the number of pearls and the weight in grains often being noted on each necklace.

The principal selling centers were Paris, London, Bombay, New York, Chicago, Los Angeles, Tokyo, and Kobe. But disturb­ances caused by the outbreak of war in 1939 gradually brought the industry to a standstill. Further, tidal waves and other natural disasters added to the destruction of the oysters. But new equip­ment and materials have been brought to the breeding grounds, and the industry has been revived. Exports of pearls are, how­ever, controlled, and most of the pearls are being sold to the U.S.A.

It was in March 1935 that the first experiment by which 3,000 white Banda shells, native oysters of New Guinea, were trans­planted successfully to Palao. Further shipments were then made, and the transplanted oysters were cultivated profitably. This has led to similar experiments being made from other areas.

Pearl cultivation entails the careful watching of the progress of the pearl oyster in its work. Frequent examinations for possible disease and periodic cleansing of the cages in which they are housed are necessary. The chief enemies of the growing oyster are various micro-organisms in the sea currents, and octopi. In each crop, barely one-tenth is fine pearls; about 20 per cent are round, 30 per cent are baroque, and the rest is unusable rubbish. Large pearls over about five grains in weight are, of course, mainly composed of shell nuclei; the cultured portion hardly merits their being called pearls at all. Smaller pearls have a relatively thicker coating of natural pearl, as a rule, while in the cheaper qualities the covering is so thin that the mother-of-pearl bead can be seen distinctly by a strong light.

The production of cultured pearls has also been developed by a Californian scientist, La Place Bostwick, who claims to have produced pearls of a large size, at the same time controlling color and size. The method is the same as is used by the Japanese, but abalone found off the coast of La Jolla, California, are used. These are collected, and the pearly nacre nucleus is inserted in the lab­oratory. The abalone is then placed in a tank of sea water which is kept at a constant temperature. Not many well shaped pearls are produced, but their beauty is claimed to approach that of the ordinary cultivated variety.

All the different shades of the real pearl have been seen in cul­tured pearls, but the rosee is the favorite, and some very beautiful necklaces are to be had, despite the shoals of rubbish which are normally offered. Black cultured pearls which tend to lose their lustre quickly, are occasionally seen, but the demand for them is small. Imitations of black pearls have been made, the best in color being of polished hematite. Of the other forms of imitation pearls, we will give some description in another chapter.

The detection of cultured pearls is not always obvious, espe­cially in the better qualities, but the dealer and pearl merchant are seldom in doubt. If a superficial examination is not sufficient (cultured pearls sometimes have small convex marks and small blackish spots on their surface), there is a mechanical test which clearly shows certain effects, these differing from those in the genuine pearl. If the specimen could be sliced, the size and the na­ture of the nucleus would immediately show its origin. The large nucleus, generally a mother-of-pearl bead, makes all the differ­ence, and it is on this that scientific tests for detection are based.

An examination of the drill hole with a lens often reveals the dividing line between the skin and the bead nucleus. Although the cheap qualities possess nothing more than a thin film of nacre, which often splits and falls away from the mother-of-pearl like an egg shell, the better qualities have a nacre thickness of about one half to two and a half millimeters, These latter take about five years to produce, but the thickest skin does not necessarily pro­duce the best pearl in appearance, as is often believed.

The luster of cultured pearls is often somewhat greasy com­pared with the natural pearl. Their specific gravity is generally slightly higher, 2.735 or 2.80, compared with about 2.715, as the mother-of-pearl nucleus is denser than the outer covering. A rough test, therefore, would be to place specimens in a solution of bromoform, the density of which should be lowered to 2.73. If the pearls sink, they are probably cultured.

Although specific gravity tests help to distinguish between the different varieties of pearls, these tests cannot be conclusive since both natural and cultured pearls vary. To be more exact, the heavy liquids used in the laboratory should have densities varying from 2.70 to 2.76, and these may be prepared by adding mono-bromonaphthaline (density 1.5) to bromoform (density 2.9). The pearls should not be kept in this mixture longer than necessary, and they should be rinsed in benzine or toluene after testing to avoid injury. This liquid should be handled with care as it is toxic.

Most natural pearls from the Persian Gulf have a specific grav­ity which falls between 2.68 and 2.74; Australian pearls should give a figure of about 2.74, and freshwater pearls a lower figure still. On the other hand, some natural pearls give a reading of only 2.30. The mother-of-pearl bead, which forms about sixty per cent by weight of the cultured pearl, has a specific gravity of 2.80 to 2.85, and the covering nacre 2.63 to 2.70. This nacre is, of course, rarely more than one millimeter in thickness. The specific gravity of the cultured pearl will therefore fall generally between 2.74 and 2.78, appreciably higher than that of the natural pearl. But the fact that the specimen sinks or floats when tested with this liquid is not an infallible test of its origin.

The drill holes in genuine pearls are often no smaller than those in cultured pearls, nor are they always perfectly straight in either variety. If any doubt exists regarding given specimens, an instrument known as the endoscope should be used. This is an improvement on the nacrescope, which was formerly in use, and a description of this instrument and the effects it shows will be found in a later chapter.

There is, of course, a vast difference between the values of cul­tured and natural pearls. Like all precious gems, the natural pearl always has an international market value; the cultured pearl has almost none. Political disturbances may cause a scarcity of cul­tured pearls, and their value may rise, but this can be only of a temporary nature. During the years 1939 to 1945, practically none was produced, and during that period demand forced up their price to something like twenty times their pre-1939 value. Pro­duction commenced once again in 1948, but no great number of necklaces were seen on the market for some three years or so. Then their value began to fall again, but they have not yet reached the low prices which were common in 1939. Natural pearls, on the other hand, have shown a gradual increase in price for some years now, although their peak value, which was reached about thirty years ago, has not yet been approached.

Real pearls retain their natural form and sheen for a much longer period than do cultured pearls; there is no outer covering to crack or split, and the very limited quantity fished each year tends to keep up their price. Their beauty and rarity will always cause them to be sought by the discriminating, for a fine pearl can be said to be the most perfect natural gem.

It is difficult to assign a place to the cultured pearl, but perhaps it might be classed with synthetics although chemically it is not a synthetic product in so far as both Nature and man have com­bined to produce it. Dealers in pearls and precious stones have little regard for cultured pearls, but apart from this natural prejudice, it must be admitted that these pearls resemble the real much more closely than do synthetic stones resemble the natural products which they try to copy. Apart from other considerations, synthetic sapphires and rubies very seldom approach the natural varieties in their superficial qualities, such as color, but cultured pearls abound which look very much like the natural pearl. There is just that difference—the hand of man has intervened, with the result that the product cannot be classed as a natural one.