which bear excrescences, or are honeycombed by boring parasites,
are those most likely to yield pearls.
The substance of a pearl is essentially the same as that which lines the interior of many shells and is known as “mother-of-pearl.” Sir D. Brewster first showed that the iridescence of this substance was an optical phenomenon due to the interference of rays of light reflected from microscopic corrugations of the surface—an effect which may be imitated by artificial striations on a suitable medium. When the inner laminated portion of a nacreous shell is digested in acid the calcareous layers are dissolved away, leaving a very delicate membranous pellicle, which, as shown by Dr Carpenter, may retain the iridescence as long as it is undisturbed, but which loses it when pressed or stretched.
It is obvious that if a pearl presents a perfectly spherical form it must have remained loose in the substance of the muscles or other soft tissues of the mollusc. Frequently, however, the pearl becomes cemented to the interior of the shell, the point of attachment thus interfering with its symmetry. In this position it may receive successive nacreous deposits, which ultimately form a pearl of hemispherical shape, so that when cut from the shell it may be flat on one side and convex on the other, forming what jewelers know as a “perle bouton.” In the course of growth the pearl may become involved in the general deposit of mother-of-pearl, and be ultimately buried in the substance of the shell. It has thus happened that fine pearls have occasionally been unexpectedly brought to light in cutting up mother-of-pearl in the workshop.
When a pearl oyster is attacked by a boring parasite the mollusc protects itself by depositing nacreous matter at the point of invasion, thus forming a hollow body of irregular shape known as a “blister pearl.” Hollow warty pearl is sometimes termed in trade “coq de perle.” Solid pearls of irregular form are often produced by deposition on rough objects, such as small fragments of wood, and these, and in fact all irregular-shaped pearls, are termed “perles baroques,” or “barrok pearls.” It appears that the Romans in the period of the Decline restricted the name unio to the globular pearl, and termed the baroque margaritum. It was fashionable in the 16th and 17th centuries to mount curiously shaped baroques in gold and enamel so as to form ornamental objects of grotesque character. A valuable collection of such mounted pearls by Dinglinger is preserved in the Green vaults at Dresden.
A pearl of the first water should possess, in jewelers’ language, a perfect “skin” and a fine “orient”; that is to say, it must be of delicate texture, free from speck or flaw, and of clear almost translucent white colour, with a subdued iridescent sheen. It should also be perfectly spherical, or, if not, of a symmetrical pear-shape. On removing the outer layer of a pearl the subjacent surface is generally dull, like a dead fish-eye, but it occasionally happens that a poor pearl encloses a “lively kernel,” and may therefore be improved by careful peeling. The most perfect pearl in existence is said to be one, known as “La Pellegrina,” in the museum of Zosima in Moscow; it is a perfectly globular Indian pearl of singular beauty, weighing 28 carats. The largest known pearl is one of irregular shape in the Beresford Hope collection at the Victoria and Albert Museum. This magnificent pearl weighs 3 oz., has a circumference of 412 in., and is surmounted by an enamelled and jewelled gold crown, forming a pendant of great value.
Pearl Fisheries.—The ancients obtained their pearls chiefly from India and the Persian Gulf, but at the present time they are also procured from the Sulu seas, the coast of Australia, the shores of Central America and some of the South Pacific Islands. The ancient fisheries of Ceylon (Taprobane) are situated in the Gulf of Manaar, the fishing-banks lying from 6 to 8 m. off the western shore, a little to the south of the isle of Manaar. The Tinnevelly fishery is on the Madras side of the strait, near Tuticorin. These Indian fishing-grounds are under the control of government inspectors, who regulate the fisheries. The oysters yield the best pearls at about four years of age. Fishing generally commences in the second week in March, and lasts for from four to six weeks, according to the season. The boats are grouped in fleets of from sixty to seventy, and start usually at midnight so as to reach the oyster-banks at sunrise. Each boat generally carries ten divers. On reaching the bank a signal-gun is fired, and diving commences. A stone weighing about 40 ℔ is attached to the cord by which the diver is let down. The divers work in pairs, one man diving while the other watches the signal-cord, drawing up the sink-stone first, then hauling up the baskets of oysters, and finally raising the diver himself. On an average the divers remain under water from fifty to eighty seconds, though exceptional instances are cited of men remaining below for as long as six minutes. After resting for a minute or two at the surface, the diver descends again; and so on, until exhausted, when he comes on board and watches the rope, while his comrade relieves him as diver. The native descends naked, carrying only a girdle for the support of the basket in which he places the pearl oysters. In his submarine work the diver makes skilful use of his toes. To arm himself against the attacks of the sharks and other fishes which infest the Indian waters he carries spikes of ironwood; and the genuine Indian diver never descends without the incantations of shark-charmers, one of whom accompanies the boat while others remain on shore. As a rule the diver is a short-lived man.
The diving continues from sunrise to about noon, when a gun is fired. On the arrival of the fleet at shore the divers carry their oysters to a shed, where they are made up into four heaps, one of which is taken by the diver. The oysters are then sold by auction in lots of 1000 each. The pearls, after removal from the dead oysters, are “classed” by passing through a number of small brass colanders, known as “baskets,” the holes in the successive vessels being smaller and smaller. Having been sized in this way, they are sorted as to colour, weighed and valued. Since the days of the Macedonians pearl-fishing has been carried on in the Persian Gulf. It is said that the oyster-beds extend along the entire Arabian coast of the gulf, but the most important are on sandbanks off the islands of Bahrein. The chief centre of the trade is the port of Lingah. Most of the products of this fishery are known as “Bombay pearls,” from the fact that many of the best are sold there. The shells usually present a dark colour about the edges, like that of “smoked pearl.” The yellow-tinted pearls are sent chiefly to Bombay, while the whitest go to Bagdad. Very small pearls, much below a pea in size, are generally known as “seed-pearls,” and these are valued in India and China as constituents of certain electuaries, while occasionally they are calcined for chunam, or lime, used with betel as a masticatory. There is a small pearl-fishery near Karachi on the coast of Bombay.
From the time of the Ptolemies pearl-fishing has been prosecuted along the coast of the Red Sea, especially in the neighbourhood of Jiddah and Koseir. This fishery is now insignificant, but the Arabs still obtain from this district a quantity of mother-of-pearl shells, which are shipped from Alexandria, and come into the market as “Egyptians.”
Very fine pearls are obtained from the Sulu Archipelago, on the north-east of Borneo. The mother-of-pearl shells from the Sulu seas are characterized by a yellow colour on the border and back, which unfits them for many ornamental purposes. Pearl oysters are also abundant in the seas around the Aru Islands to the south-west of New Guinea. From Labuan a good many pearl-shells are occasionally sent to Singapore. They are also obtained from the neighbourhood of Timor, and from New Caledonia. The pearl oyster occurs throughout the Pacific, mostly in the clear water of the lagoons within the atolls, though fine shells are also found in deep water outside the coral reefs. The Polynesian divers do not employ sink-stones, and the women are said to be more skilful than the men. They anoint their bodies with oil before diving. Fine pearl-shells are obtained from Navigators’ Islands, the Society Islands, the Low Archipelago or Paumota Isles and the Gambier Islands. Many of the Gambier pearls present a bronzy tint.
Pearl-fishing is actively prosecuted along the western coast of Central America, especially in the Gulf of California, and to a less extent around the Pearl Islands in the Bay of Panama. The
