PEARLS VALUE

But, apart from market fluctuations, small defects in pearls make such a vast difference to their value that only a pearl expert is able to give a reliable opinion. A single pearl may be valued at $28,000 (£10,000) while a necklace composed of very small pearls, known as seed pearls, may be bought for $8.40 (£3). The unit of weight universally in use is the pearl grain, and later we shall explain the peculiar method of calculating values on the "base" system. Low quality and small seed pearls are, how­ever, bought and sold by weight, the Troy ounce being generally used. Other units of weight have been used in the past since the pearl oyster really thrives only in the warmer seas and oceans. The Persians, according to Athenaeus, sold pearls by their weight in gold, but modern methods are more exact and less costly.

As pearls are of organic origin, they are easily injured if not treated with care. They are not very hard, ranging from about 3 I/2 to 4 on Mohs' scale. Specific gravity varies generally between 2.5 and 2.9, the poor pearls being the lightest and the pinkish pearls the heaviest. This is accounted for by the fact that pinkish pearls are composed chiefly of aragonite, whose density is about 2.93. Calcite has a density of 2.71 or 2.72. The average specific gravity of pearl may be taken as 2.71. Fresh water pearls average about 2.68. Blue pearls, which contain a larger proportion of organic matter, are lower in density.

The best colored pearls, the rosee variety, come almost exclu­sively from the Persian Gulf, and these are rather brittle. They are known in the trade as Indian pearls, and they are the product of two varieties of pearl oysters.

About 90 per cent by weight of pearl is calcium carbonate in the form of aragonite, the remainder being organic matter and water, with a minute undetermined residue.

Heat will affect the color of pearls, and they are fairly easily scratched. They are therefore not very suitable for use in rings, unless worn occasionally. They are, however, mounted as earrings and in brooches, pendants, studs, and other forms of jewelry, but it is as earrings and necklaces that they are in most demand. A necklace of even color and good graduation is not easy to collect, and this is the reason for round pearls obtaining the highest prices. Shades vary so much that great experience is required to match pearls. Original consignments of Indian pearls are often sent to Europe and America in short strung rows, tied together in bunches, and finished off with brightly colored tassels. It would need such a bunch valued at many thousands of dollars to make up even a few well matched and graded necklaces.

Any acid will readily attack pearl, since it is chiefly composed of calcium carbonate. Perspiration also has a detrimental effect in many instances, particularly if it is of an acid nature, for the sur­face of the pearl will absorb the liquid with the result that the color may change. In addition, the holes of drilled pearls in neck­laces tend to become larger in wear owing to the constant friction of the stringing material. For this reason, necklaces should be regularly re-strung and knotted between each pearl. The holes in old pearls may be so large that they may have to be plugged and re-drilled. The quills of birds' feathers are often used for this purpose.

The improvement of some pearls by skinning is sometimes un dertaken, but it is a risky process, even for the experienced. The dull surface is carefully removed by using fine sandpaper or a file, but a lower layer may reveal fresh blemishes, and consid­erable experience and skill are required before such an operation may be undertaken with any success. It has always to be borne in mind that a small loss in weight reduces value tremendously; only by uncovering a surface of better color and with less faults than the original can the value be increased. There are very few ex­perts who follow this occupation; they are usually capable of improving pearls in other respects. Internal cracks may be sometimes eliminated, but external cracks are permanent. The round­ing of oval pearls is not such a difficult operation, and it is often carried out successfully on old pearls.

Although many methods of retaining the fresh sheen on pearls are advised, there is no certain means of preservation, but they should certainly be kept away from extremes of temperature. On account of their soft nature, wear is inevitable. The organic mat­ter also very gradually decays, and covering them with flour, keeping them in sea-water, and excluding them from light when not in use are all of little assistance. Another method sometimes mentioned is to retain pearls in dry magnesia, while to make a pigeon swallow a pearl and allow it to remain in the crop of the bird for a limited time is a fantastic notion of restoring color, although this has been seriously advised by more than one writer.

It has already been noted that the rarest and most prized shade is the rosee. Following this in value come the white rosee, cream, white, pale bluish-white, brown rosee, and yellow rosee. Last come the browns, grays, and yellows, but the fancy colors, green and black, are valuable if of good shape and if the sheen is almost metallic. The perfect pearl is round, of rosee color throughout, and it shows no spots, indentations, lumps, cracks, or veins. A close examination in natural light, away from any colored back­ground, and with the aid of a magnifier, will reveal all faults and virtues. A strung necklace should have a gradual fall in size from the center, and the end pearls should be proportionate to the center in size. The matching in color and size is of great impor­tance.