1911 Encyclopædia Britannica/Pearl
PEARL. Pearls are calcareous concretions of peculiar lustre, produced by certain molluscs, and valued as objects of personal ornament. 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 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 Erst 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 4½ 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 fishing-grounds are in water about 40 ft. 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. 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 good pearls have been 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 established 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. Pearl-shells have also been found at Port Darwin and in Oakley Creek, New Zealand.
River pearls are produced by the species of Unio and Anodonta, especially by Unio margaritiferus. These species belong to the family Unionidae, order Eulamellebranchia. They inhabit the mountain streams of temperate climates in the northern hemisphere especially 1n Scotland, Wales, Ireland, Saxony, Bohemia, Bavaria, Lapland and Canada. The pearls of Britain are mentioned 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. The Scotch pearl-fishery, after having declined for years, was revived in 1860 by a German named Moritz Unger, who 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, and 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 celebrated for its pearls; and it is related that Sir Richard Wynn, chamberlain to the queen of Charles II, presented her with a Conway 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 Hawkins 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 Ratisbon 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 regulated 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, and also on the Mississippi, especially about Muscatine, Iowa. The season extends from June to October. Japan produces fresh-water pearls, found especially in the Anodonta 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 Rh'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 inserted 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 ob]ects 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 nightsoil 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 which 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 previously described. 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 possibility of producing artificial pearls in the fresh-water 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. The common marine mussel Mytilus edulis also produces pearls, which are, however, of little value.
According to the latest researches the cause of pearl-formation is in most cases, perhaps in all, the dead body of a minute parasite within the tissues of a mollusc, around which nacreous deposit is secreted. The parasite is a stage in the life history of a Trematode in some cases, in others of a Cestode; that is to say of a form resembling the common liver-fluke of the sheep, or of a tapeworm. As long ago as 1852 Filippi of Turin showed that the species of Trematode Distomum duplicatum was the cause of a pearl formation in the fresh-water mussel Anodanta. Kuchenmeister subsequently investigated the question at Elster in Saxony and came to a different conclusion, namely that the central body of the pearl was a small specimen of a species of water mite which is a very common parasite of Anadonta. Filippi however states that the mite is only rarely found within a pearl, the Trematode occurring in the great majority of cases. R. Dubois and Dr H. Lyster Jameson have made special investigations of the process in the common mussel Mytilus edulis. The latter states that the pearl is produced in a sac which is situated beneath the epidermis of the mantle and is lined by an epithelium. This epithelium is not derived from the cells of the epidermis but from the internal connective-tissue cells. This statement, if correct, is contrary to what would be expected, for calcareous matter is usually secreted by the external epidermis only. The sac or cyst is formed by the larva of a species of Trematode belonging to the genus Leucithodendrium, a species closely resembling and probably identical with L. somateriae, which lives in the adult state in the eider duck. At Billiers, Morbihan, in France, the host of the adult Trematode is another species of duck, namely the common Scoter, Oedemia nigra, which is notorious in the locality for its avidity for mussels. Trematodes of the family Distomidae, to which the parasite under consideration belongs, usually have three hosts in each of which they pass different stages of the life history. In this case the first host at Billiers is a species of bivalve called Tapes decussatus, but at Piel in Lancashire there are no Tapes and the first stages of the parasite are found in the common cockle. The Trematode enters the first host as a minute newly hatched embryo and leaves it in the form called Cercaria, which is really an immature condition of the adult. The Cercaria makes its way into the tissues of a mussel and there becomes enclosed in the cyst previously described. If the mussel is then swallowed by the duck the Cercariae develop into adult Trematodes or flukes in the liver or intestines of the bird. In the mussels which escape being devoured the parasites cannot develop further, and they die and become embedded in the nacreous deposit which forms a pearl. Dr Jameson points out that, as in other cases, pearls in Mytilus are common in certain special localities and rare elsewhere, and that the said localities are those where the parasite and its hosts are plentiful.
The first suggestion that the most valuable pearls obtained from pearl oysters in tropical oceans might be due to parasites was made by Kelaart in reports to the government of Ceylon in 1857–1859. Recently a special investigation of the Ceylon pearl fishery has been organized by Professor Herdman. Herdman and Hornell find that in the pearl oyster of Ceylon Margaritifera vulgaris, Schum, the nucleus of the pearl is, in all specimens examined, the larva of a Cestode or tapeworm. This larva is of globular form and is of the type known as a cysticercus. As in the case of the mussel the larva dies in its cyst and its remains are enshrined in nacreous deposit, so that, as a French writer has said, the ornament associated in all ages with beauty and riches is nothing but the brilliant sarcophagus of a worm.
The cysticercus described by Herdman and Hornell has on the surface a muscular zone within which is a depression containing a papilla which can be protruded. It was at first identified as the larva of a tapeworm called Tetrarhynchus, and Professor Herdman concluded that the life-history of the pearl parasite consisted of four stages, the first being exhibited by free larvae which were taken at the surface of the sea, the second that in the pearl oyster, the third a form found in the bodies of file-fishes which feed on the oysters, and the fourth or adult stage living in some species of large ray, It has not however been proved that the pearl parasite is a Tetrarhynchus, nor that it is connected with the free larva or the form found in the file-fish, Batistes; nor has the adult form been identified. All that is certain is that the pearls are due to the presence of a parasite which is the larva of a Cestode, all the rest is probability or possibility. A French naturalist, M. Seurat, studying the pearl oyster of the Gambier Archipelago in the Pacific, found that pearl formation was due to a parasite quite similar to that described by Herdman and Hornell. This parasite was described by Professor Giard as characterized by a rostrum armed with a single terminal sucker and he did not identify it with Tetrarhynchus.
Genuine precious pearls and the most valuable mother-of-pearl are produced) by various species and varieties of the genus Meleagrina of Lamarck, for which Dr Jameson in his recent revision of the species prefers the name Margaritifera. The genus is represented in tropical regions in all parts of the world It belongs to the family Aviculidae, which is allied to the Pectens or scallop shells. In this family the hinge border is straight and prolonged into two auricular; the foot has a very stout byssus Meleagrina is distinguished by the small size or complete absence of the posterior auricula. The species are as follows, The type species is Meleagrina margaritifera, which has no teeth on the hinge. Geographical races are distinguished by different names in the trade. Specimens from the Malay Archipelago have a dark band along the margin of the nacre and are known as black-edged Banda shell; those from Australia and New Guinea and the neighbouring islands of the western Pacific are called Australian and New Guinea black-lip. Another variety occurs in Tahiti, Gambier Islands and Eastern Polynesia generally, yielding both pearls and shell. It occurs also in China, Ceylon, the Andaman Islands and the Maldives. Another form is taken at Zanzibar, Madagascar, and the neighbouring islands, and is called Zanzibar and Madagascar shell. Bombay shell is another local form fished in the Persian Gulf and shipped via Bombay. The Red Sea variety is known as Egyptian shell. Another variety occurs along the west coast of America and from Panama to Vancouver, and supplies Panama shell and some pearls. A larger form, attaining a foot in diameter and a weight 10 ℔ per pair of shells, is considered as a distinct species by Dr Jameson and named Margaritifera maxima. It is found along the north coast of Australia and New Guinea and the Malay Archipelago. The nacreous surface of this shell is white, without the black or dark margin of the common species; it is known in the trade as the silver-lip, gold-lip and by other names. It is the most valuable species of mother-of-pearl oyster. Dr Jameson distinguishes in addition to the above thirty-two species of Margaritifera or Meleagrina; all these have rudimentary teeth on the hinge. The most important species is Meleagrina vulgaris, to which belong the pearl oyster of Ceylon and southern India, the lingah shell of the Persian Gulf and the pearl oyster of the Red Sea. Since the opening of the Suez Canal the latter form has invaded the Mediterranean, specimens having been taken at Alexandria and at Malta, and attempts have been made to cultivate it on the French coast. The species occurs also on the coasts of the Malay Peninsula, Australia and New Guinea, where it is fished both for its shells (Australian lingah) and for pearls. Two species occur on the coasts of South Africa but have no market value. Meleagrina carchariarum is the Shark's Bay shell of the London market. It is taken in large quantities at Shark's Bay, Western Australia, and is of rather small value; it also yields pearls of inferior quality. The pearl oyster of Japan, known as Japan lingah, is probably a variety of Meleagrina vulgaris. Meleagrina radiata is the West Indian pearl oyster.
The largest and steadiest consumption of mother-of- earl is in the button trade, and much is also consumed by cutlers for handles of fruit and dessert knives and forks, pocket-knives, &c. It is also used in the inlaying of Japanese and Chinese lacquers, European lacquered papier-mâché work, trays, &c., and as an ornamental inlay generally. The carving of pilgrim shells and the elaboration of crucifixes and ornamental work in mother-of-pearl is a distinctive industry of the monks and other inhabitants of Bethlehem. Among the South Sea Islands the shell is largely fashioned into fishing-hooks. Among shells other than those of Meleagrina margaritifera used as mother-of-pearl may be mentioned the Green Ear or Ormer shell (Haliotis tnberculata) and several other species of Haliotis, besides various species of Turbo.
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. Many imitation pearls are now formed of an opaline glass of nacreous 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 jewelry," 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 Clements R. Markham, “ The Tinnevelly Pearl Fishery,” in Journ. Soc. Arts (1867), xv., 256; D. T. Macgowan, “ Pearls and Pearl-making in China," ibid. (1854), ii. 72; Hague, " On the Natural and Artificial Production of Pearls in China,” in Journ. Roy. Asiatic Soc. (1856), vol. xvi; H. J. Le Beck, “ Pearl Fishery in the Gulf of Manar," in Asiatic Researches (1798), v. 393; K. Mobius, Die echten Perlen (Hamburg, 1857); H. Lyster Jameson, “ Formation of Pearls," Proc. Zool. Soc (1902), pl. 1; idem, “ On the Identity and Distribution of Mother-of-Pearl Oysters,” Proc. Zool. Soc. (1901), pl, 1, pp. 372–394; Herdman and Hornell, Rep. Ceylon Pearl Fisheries (London, Royal Soc., 1903); and Kunz and Stevenson, Book of the Pearl (New York, 1908), with bibliography. (J. T. C.)
- Strombus gigas, L., is a Gastropod belonging to the family Strombidae, of the order Pectinibranchia. Turbinella scolymus, Lam, is a Gastropod of the same order.
- Placuna placenta, L., belongs to the family Anomiidae; it is found on the shores of North Australia. Pinna squamosa, Gmelin, belongs to the Ostreacea; it occurs in the Mediterranean. Both are Lamellibranchs.