PEARL. Pearls are calcareous concretions of peculiar lustre, produced by certain molluscs, and valued as objects of personal ornament. It is believed that most pearls are formed by the intrusion of some foreign substance between the mantle of the mollusc and its shell, which, becoming a source of .irritation, determines the deposition of nacreous matter in concentric layers until the substance is com-pletely encysted. The popular notion that the disturbing object is commonly a grain of sand seems untenable; according to Dr Gwyn Jeffreys and some other concho-logists, it is in most cases a minute parasite; while Dr Kelaart has suggested that it may be the frustule of a diatom, or even one of the ova of the pearl-producing mollusc itself. The experience of pearl-fishers shows that those shells which are irregular in shape and stunted in growth, or 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 micro-scopic 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.
Although a large number of molluscs secrete MOTHER-OF-PEARL (q.v.), only a few of them yield true pearls. The finest are obtained from the so-called "pearl oyster," the Avicuia (Meleagrina) margaritifera, Linnseus, while fresh-water pearls are procured chiefly from the "pearl mussel," JJnio (Margaritana) margaritiferus, L. These river-pearls are generally of dull leaden hue, and inferior in beauty to those of marine origin.
It is obvious that if a pearl presents a perfectly spheri-cal form it must have remained loose in the substance of the muscles or other soft tissues of the mollusc. Fre-quently, however, the pearl becomes cemented to the in-terior of the shell, the point of attachment thus interfering with its symmetry. In this position it may receive suc-cessive 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 jewellers know as a "perle bouton." In the course of growth the pearl may become involved in the general de-posit 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 jewellers' 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 re-moving 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, weigh-ing 28 carats. The largest known pearl is one of irregu-lar shape in Mr Beresford Hope's collection at the South Kensington museum. This magnificent pearl weighs 3 oz., has a circumference of 4| inches, 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 miles 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 Govern-ment inspectors, who regulate the fisheries, and permit fishing only when they consider the banks to be in a satis-factory condition. The oysters yield the best pearls at about four years of age. Fishing, when permitted, gener-ally 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 com-mences. To facilitate the descent of the diver, a stone of granite weighing about 40 lb is attached to the cord by which he 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 some can endure a much longer submergence, and 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. Using neither diving dress nor bell, the native descends naked, carrying only a girdle for the sup-port of the basket in which he places the pearl-oysters. In his submarine work the diver makes skilful use of his toes for prehensile purposes. 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 incanta-tions of shark-charmers, one of whom accompanies the boat while others remain on shore. Not only is the diver exposed to the danger of attack by sharks, but his exciting calling, in a tropical climate, is necessarily ex-hausting, and as a rule he is a short-lived man.
The diving continues from sunrise to about noon, when a gun is fired, and the work stopped. 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 as his remuneration. 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 cullenders, 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. (For the history and production of the Ceylon fishery, see CEYLON, vol. v. p. 364.)
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. According to Colonel Pelly's report in 1863, there were 1500 boats belonging to Bahrein alone, and the annual profit from the pearl-fishery was about ¿£400,000. 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 Baghdad. 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 electu-aries, while occasionally they are calcined for chunam, or lime, used with betel as a masticatory. There is a small pearl-fishery near Kurrachee 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 orna-mental 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. These pearls are obtained from the Meleagrina californica, Cpr., and the mother-of-pearl shell is known in commerce as "Panama" or "bullock" shell. The fishing-grounds are in water about 40 feet deep, and the season lasts for four months. An ordinary fishing-party expects to obtain about three tons of shells per day, and it is estimated that one shell in a thousand contains a pearl. The pearls are shipped in barrels from San Francisco and Panama. Some pearls of rare beauty have been obtained from the Bay of Mulege, near Los Coyetes, in the Gulf of California; and in 1882 a pearl of 75 carats, the largest on record from this district, was found near La Paz in California. The coast of Guayaquil also yields pearls. Columbus found that pearl-fishing was carried on in his time in the Gulf of Mexico, and pearls are still obtained from the Caribbean Sea. These are produced chiefly by Meleagrina squamulosa, Lam.; and the mother-of-pearl shells are known as " blue-edged "or " black-lijjped," these being less valuable than the " silver-lipped" shells of India. In the West Indies the best pearls are obtained from St Thomas and from the island of Margarita, off the coast of Venezuela. From Margarita Philip II. of Spain is said to have obtained in 1579 a famous pearl of 250 carats.
Of late years pearl-fishing has been started with con-siderable success in the Australian seas. Good pearls are found in Shark's Bay, on the coast of West Australia, especially in an inlet termed Useless Harbour. Mother-of-pearl shells are also fished at many other points along the western coast, between the 15th and 25th parallels of south latitude. An important pearl-fishery is also estab-lished in Torres Strait and on the coast of Queensland. The shells occur in water from four to six fathoms deep, and the divers are generally Malays and Papuans, though sometimes native Australians. On the western coast of Australia the pearl-shells are obtained by dredging rather than by diving. Quite recently (1884) pearl-shells have been found at Port Darwin. Pearls have also been found in Oakley Creek, New Zealand.
River-pearls are produced by the fresh-water mussels inhabiting the mountain-streams of temperate climates in the northern hemi-sphere,— especially in Scotland, Wales, Ireland, Saxony, Bohemia, Bavaria, Lapland, and Canada. The pearls of Britain are men-tioned by Tacitus and by Pliny, and a breastplate studded with British pearls was dedicated by Julius Caesar to Venus Genetrix. As early as 1355 Scotch pearls are referred to in a statute of the goldsmiths of Paris ; and in the reign of Charles II. the Scotch pearl trade was sufficiently important to attract the attention of parliament. Writing in 1705, John Spruel says, " I have dealt in pearls these forty years and more, and yet to this day I could never sell a necklace of fine Scots pearl in Scotland, nor yet fine pendants, the generality seeking for Oriental pearls, because farther fetched. At this very day I can show some of our own Scots pearl as fine, more hard and transparent, than any Oriental" (An Account Current betwixt Scotland and England, Edinburgh, 1705). The Scotch pearl-fishery, after having declined for years, was revived in 1860 by a German named Moritz Unger, wdio visited Scotland and bought up all the pearls he could find in the hands of the peasantry, thus leading to an eager search for more pearls the following season. It is estimated that in 1865 the produce of the season's fishing in the Scotch rivers was worth at least £12,000. This yield, however, was not maintained ; the rivers were over-fished, and the industry was discouraged inasmuch as it tended to interfere with the salmon-fishery, and in some cases injured the banks of the streams. At the present time only a few pearls are obtained at irregular intervals by an occasional fisherman.
The principal rivers in Scotland which have yielded pearls are the Spey, the Tay, and the South Esk ; and to a less extent the Doon, the Dee, the Don, the Ythan, the Teith, the Forth, and many other streams. In North Wales the Conway was at one time cele-brated for its pearls; and it is related that Sir Richard Wynn, chamberlain to the queen of Charles II., presented her with a Con-way pearl which is believed to occupy a place in the British crown. In Ireland the rivers of Donegal, Tyrone, and Wexford have yielded pearls. It is said that Sir John Hawddns the circumnavigator had a patent for pearl-fishing in the Irt in Cumberland. Although the pearl-fisheries of Britain are now neglected, it is otherwise with those of Germany. The most important of these are in the forest-streams of Bavaria, between Batisbon and Passau. The Saxon fisheries are chiefly confined to the basin of the White Elster, and those of Bohemia to the Horazdiowitz district of Wotawa. For more than two centuries the Saxon fisheries have been carefully re-gulated by inspectors, who examine the streams every spring, and determine where fishing is to be permitted. After a tract has been fished over, it is left to rest for ten or fifteen years. The fisher folk open the valves of the mussels with an iron instrument, and if they find no pearl restore the mussel to the water.
River-pearls are found in many parts of the United States, and have been systematically worked in the Little Miami river, Warren county, Ohio. The season extends from June to October. Japan produces freshwater pearls, found especially in the Anodonia japonica. But it is in China that the culture of the pearl-mussel is carried to the greatest perfection. The Chinese also obtain marine pearls, and use a large quantity of mother-of-pearl for decorative purposes. More than twenty-two centuries before our era pearls are enumerated as a tribute or tax in China ; and they are mentioned as products of the western part of the empire in the jtth'ya, a dictionary compiled earlier than 1000 B.C. A process for promoting the artificial formation of pearls in the Chinese river-mussels was discovered by Ye-jin-yang, a native of Hoochow, in the 13th century ; and this process is still extensively carried on near the city of Teh-tsing, where it forms the staple industry of several villages, and is said to give employment to about 5000 people. Large numbers of the mussels are collected in May and June, and the valves of each are gently opened with a spatula to allow of the introduction of various foreign bodies, which are in-serted by means of a forked bamboo stick. These "matrices" are generally pellets of prepared mud, but may be small bosses of bone, brass, or wood. After a number of these objects have been placed in convenient positions on one valve, the unfortunate mollusc is turned over and the operation is repeated on the other valve. The mussels are then placed in shallow ponds connected with the canals, and are nourished by tubs of night-soil being thrown in from time to time. After several months, in some cases two or three years, the mussels are removed, and the pearls which have formed over the matrices are cut from the shells, while the molluscs themselves serve as food. The matrix is generally extracted from the pearl and the cavity filled with white wax, the aperture being neatly sealed up so as to render the appearance of the pearl as perfect as possible. Millions of such pearls are annually sold at Soo-chow. The most curious of these Chinese pearls are those wdiich present the form of small seated images of Buddha. The figures are cast in very thin lead, or stamped in tin, and are inserted as previ-ously described. As many as twenty may sometimes be seen, ranged in parallel rows, in the valves of a single individual. Covered with nacreous matter, closely adherent to the shell, they have all the appearance of natural objects, and, exciting the wonder of the ignorant, are prized as amulets. Specimens of these Buddha pearls in the British Museum are referred to the species Dipsas plicata. It should be mentioned that Linnaeus, probably ignorant of what had long been practised in China, demonstrated the pos-sibility of producing artificial pearls in the freshwater mussels of Sweden.
Pink pearls are occasionally found in the great conch or fountain shell of the West Indies, Strombus gigas, L. ; but these, though much prized, are not nacreous, and their tint is apt to fade. They are also produced by the chank shell, Turbinella scolymus, L. Yellowish-brown pearls, of little or no value, are yielded by the Pinna squamosa, and bad-coloured concretions are formed by the Placuna placenta.' Black pearls, which are very highly valued, are obtained chiefly from the pearl-oyster of the Gulf of Mexico.
Artificial pearls were first made in western Europe in 1680 by Jacquin, a rosary-maker in Paris, and the trade is now largely carried on in France, Germany, and Italy. Spheres of thin glass are filled with a preparation known as '' essence d'orient,'' made from the silvery scales of the bleak or ' ablette," which is caused to adhere to the inner wall of the globe, and the cavity is then filled with white wax. The scales are in some cases incorporated with celluloid. Many imitation pearls are now formed of an opaline glass of nacre-ous lustre, and the soft appearance of the pearl obtained by the judicious use of hydrofluoric acid. An excellent substitute for black pearl is found in the so-called "ironstone jewellery," and consists of close-grained haematite, not too highly polished ; but the great density of the haematite immediately destroys the illusion. Pink pearls are imitated by turning small spheres out of the rosy part of the conch shell, or even out of pink coral.
See W. H. Dall, " Pearls and Pearl Fisheries," in American Naturalist, xvii., 1883, p. 549 ; P. L. Simmonds, The Commercial Products of the Sea (London, 1879); Clements K. Markham, " The Tinnevelly Pearl Fishery," in Journ. Soc. Arts, xv., 1867, p. 256 ; D. T. Maegowan, " Pearls and Pearl-making in China," ibid. ii., 1854, p. 72 ; F. Hague, " On the Natural and Artificial Production of Pearls in China," in Journ. Ii. Asiatic Soc., xvi., 1856 ; H. .1. Le Beck, " Pearl Fishery in the Gulf of Manar," in Asiatic Researches, v., 1798, p. 393 ; T. Von Hessling, Die Perlmuschel und ihre Perlen (Leipsic, 1859); K. Mobius, Die echten Perlen (Hamburg, 1857). (F. W. E.)
Footnotes
Meleagrina margaritifera, L., belongs to the family Avictdidw of most zoologists, to the family A viculacete, order Monomya, of article MOLLUSCA. Meleagrina is merely a sub-genus of Amcula. The animal which produces fresh-water pearls in Britain and other parts of Europe was named Unio margaritiferns by Retzius in Nova, Gen. Test., and this is the name adopted by most modern zoologists ; the animal was placed in a separate genus, Margaritana, by Schumacher for insuffi-cient reasons. It belongs to the order Isomya, family Unionacese. The molluscs from which river-pearls are obtained in the United States and other parts of the world are mostly species of Unio or Anodonta. The above are all Lamellibranchs.
Strombus gigas, L., is a Gastropod belonging to the family Strom-bidee, of the order Azygobranehia. Turbinella scolymus, Lam., is a Gastropod belonging to the family Muricidse, of the same order.
Placuna placenta, L., belongs to the family Ostreidm of the manuals (family Ostracea of article MOLLUSCA) ; it is found on the shores of North Australia. Pinna squamosa, Gmelin, belongs to the Mytilidee (the Mytilaceee of article MOLLUSCA) ; it occurs in the Medi-
I terranean. Both are Lamellibranchs.