Pearls

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Q 1.
	Are pearl oysters found in the Atlantic?
Q 2.
	How is artificial pearl culture carried on?
Q 3.
	How are pearls formed?
Q 4.
	What is a cat’s-eye pearl?
Q 5.
	How rare are conch pearls and what is their value?
Q 6.
	How are pearl shells used in the manufacture of night-luminous compasses?
Q 7.
	What is a cultured pearl and how is one made?
Q 8.
	What is pearl essence?
Q 9.
	Are pearls always spherical?
Q 10.
	I recently bought some imitation pearls. The salesclerk said they contained "pearl essence." What is this substance?
Q 11.
	My firm is primarily interested in catching menhaden fish for the production of fish meal, oil and solubles. A number of years ago we did some research concerning the removal of pearl essence from menhaden fish scales, but we were unable to develop a satisfactory, economical method. I noticed last year that the pearl essence on the scales of a species of herring available to our boats seemed to rub off very easily. Do you know of any process for removing this pearl essence from fish scales that would be feasible for us?
Q 12.
	While eating cherry stone clams last summer, I found a clam pearl which measures 0.385 inches across and 0.2875 inches from top to bottom. I have found no one who has ever seen this large a clam pearl. Have larger ones been found?
Q 13.
	We have a 30" x 18" x 7" shell from the South Pacific giant clam. Are there several layers of mother-of-pearl in this shell?
Q 14.
	How is pearl essence, also known as fish silver and essence d'orient, recovered from fish scales?
Q 15.
	During a visit to Grand Turk. Bahamas, I was shown a pear-shaped, delicate pink object which was reputed to be a conch pearl. Can you provide information about such a pearl?
Q 16.
	Do clams produce pearls? If so, do the pearls have any value?
Q 17.
	I recently purchased some oysters from Apalachicola, Florida. Upon opening one of the oysters, I found the enclosed seven hard, round objects. Are these pearls? If so, is it rare to find more than one pearl in any oyster?


_{-- a n s w e r s a b o u t P e a r l s --}
	Q&A 1.	Are pearl oysters found in the Atlantic?
	The oyster Pictada margaritifera, which is found about the coast of Venezuela and elsewhere in the Caribbean, produces pearls of high quality. The common edible oysters (Ostrea and Crassostrea sp.) also occasionally produce pearls, but these are usually of no value. The principal pearl-producing oysters are the Pacific species belonging to the Genus Margaritifera, and these do not occur in the Atlantic. Best known are the pearl oyster of the Persian Gulf, M. vulgaris, and M. maxima of northern Australia, which is the largest species. M. margaritifera erythroensis of the Persian Gulf and Ceylon only rarely yields pearls but the thick shells are sometimes used in the manufacture of mother-of-pearl.
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	Q&A 2.	How is artificial pearl culture carried on?
	The most successful pearl culture program is carried on by the Mikimoto firm of Japan, which has produced cultured pearls since about 1894. This is accomplished by introducing an irritating substance (usually a mother-of-pearl bead) into the mantle tissues of a living pearl oyster. These "treated" oysters are kept at a depth of about 35 feet in wire baskets for a period of several years, during which time the bead is coated with a layer of pearl substance secreted by the oyster. It is estimated that about 60 per cent of the treated oysters will produce cultured pearls in this manner.
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	Q&A 3.	How are pearls formed?
	Ordinarily this is caused by a grain of sand, shell fragment, parasite of microscopic size, or even a tiny fish or crab becoming lodged next to or within the body of an oyster (or in some cases, other mollusks) and setting up an irritation. The oyster host responds to this irritation by covering the foreign object with nacre, the same substance with which its shell is lined. The pearl itself then becomes the irritant and gradually builds up as layer after layer of nacre is deposited. Thus a cross-section of a mature pearl resembles that of an onion with many concentric layers, one within the other.
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	Q&A 4.	What is a cat’s-eye pearl?
	The so-called cat's-eye pearl is not an actual pearl at all, but the smooth, stony operculum (a lid-like structure blocking the shell opening) of certain sea snails of the Family Turbinidae. While the opercula of most shells are thin and horny in structure, in the Turbinidae they are solid and heavy and frequently of great beauty. Bracelets and necklaces made of cat’s-eyes from the Pacific were frequently purchased by returning G.I.’s, who mistakenly believed them to be of great value because of their appearance. Actually, cat's-eyes are fairly common in many areas.
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	Q&A 5.	How rare are conch pearls and what is their value? Homestead, Florida
	Pearls of great value are sometimes taken from the giant pink king conch, Strombus gigas, or the helmet shell, Cassis tuberosa, both of the Florida Keys, Bahamas, and West Indies. Strombus pearls are pink, while those of Cassis are usually orange-colored. Well-shaped and solid pearls from either of these conchs may be worth several thousand dollars, but the greater number obtained are small, hollow, misshapen or rough and practically worthless. As in the case of oyster pearls, conch pearls are caused by accidental irritating agent in the flesh of the mollusk. Several years ago a sum of $10,000 was paid in London for a fine pink conch pearl taken at Great Inagua in the Bahamas.
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	Q&A 6.	How are pearl shells used in the manufacture of night-luminous compasses?
	During World War II small pocket compasses were issued to troops for use during jungle patrols. The dials of the American compasses were of metal, but those issued to British and Australian troops were made of sectionsof pearl shell ground down to 1/12,000 of an inch. At this thickness the shell is translucent and is readily illuminated at night by the radium light beneath. A further advantage to this type of compass dial is that it is completely unaffected by the fluid in the compass.
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	Q&A 7.	What is a cultured pearl and how is one made? New York, New York
	Cultured pearls, like real pearls, are obtained from oysters. It was found by the Japanese that the finest pearls came from the strongest oyster. They therefore conducted careful breeding experiments and tried to raise oysters free from disease and protected from their natural enemies. To do this they put the oysters in fine meshed cages which were placed in the sea. To culture pearls in these oysters they are operated on when they are three years old. The operation consists of arranging a part of one oyster around a mother of pearl nucleus to form a sac which is then grafted into the tissue c of a second oyster. This oyster is then placed back in the sea where, for the next seven years, it will secrete nacreous material around the nucleous to form a cultivated pearl. Approximately sixty percent of the oysters treated in this manner yield pearls; however, only five percent product marketable pearls.
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	Q&A 8.	What is pearl essence? West Miami, Florida
	Pearl essence is made by several different processes which involve the removal of the guanin crystals from the scales of fish. These crystals are deposited in the epidermis of the scales and give them their luster. After processing this luster is imparted to beads of glass or other objects in the manufacture of artificial pearls. The herring, Clupea harengus, caught along the North Atlantic coast has provided much of the raw material for this trade. Recently pearl essence has been produced from herring scales from the Pacific British Columbia herring fishery. One hundred tons of fish are reported to produce one ton of scales, which produces one pound of essence.
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	Q&A 9.	Are pearls always spherical? Vero Beach, Florida
	The ultimate shape of natural or cultured pearls is determined in general by the nucleus around which it is formed. In nature the foreign particle which accidentally becomes the nucleus may be of any shape, so the resulting pearls are exceedingly varied in form. Because the nucleus which is introduced into oysters in the cultivation of pearls is round, the resulting pearls are round. When two nuclei are introduced too close together it is possible for "Siamese twin" pearls to result. Many other odd shaped pearls develop around the different nuclei. For example, the Chinese insert tiny images of Buddha under the mantle of a fresh water mussel which deposits a thin coating of pearl on the images. These pearl-covered images are sold to devout Buddhists.
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	Q&A 10.	I recently bought some imitation pearls. The salesclerk said they contained "pearl essence." What is this substance? Miami, Florida
	"Pearl essence" is prepared from the lustrous, iridescent material which occurs on the skin or scales of certain species of fish. It is used as an ingredient of a type of lacquer to give the pearly luster to imitation pearls. It is also used in the manufacture of certain types of costume jewelry and toilet articles. The pearl essence industry flourished in Japan from 1920 until 1930, when the demand dropped. Production has been encouraged by the recent development of new plastics, in which iridescence is desired.
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	Q&A 11.	My firm is primarily interested in catching menhaden fish for the production of fish meal, oil and solubles. A number of years ago we did some research concerning the removal of pearl essence from menhaden fish scales, but we were unable to develop a satisfactory, economical method. I noticed last year that the pearl essence on the scales of a species of herring available to our boats seemed to rub off very easily. Do you know of any process for removing this pearl essence from fish scales that would be feasible for us? Amagansett, New York
	There have been plants in operation for making pearl essence on both the United States and Canadian sides of the Bay of Fundy. These plants used the scales of the herring, Clupea harengus, which is found from Labrador to Sandy Hook. In Virginia and Massachusetts pearl essence is made from the scales of the alewife, Alosa pseudoharengus. For this process boats with false bottoms are used to carry the fish so that the scales drop through the rails into the bottom, leaving the fish above. The scales are cleaned with a small amount of water in an agitator and separated by centrifuge. A dilute ammonia solution is then used to dissolve the epidermis and the liquid decanted from the crystals which drop to the bottom after standing. This method provides a clean, aqueous suspension. Non-aqueous suspensions and lacquers are made by various processes, one of which is described in U.S. Bureau of Commercial Fisheries Document No. 989, which was published in 1925.
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	Q&A 12.	While eating cherry stone clams last summer, I found a clam pearl which measures 0.385 inches across and 0.2875 inches from top to bottom. I have found no one who has ever seen this large a clam pearl. Have larger ones been found? Rockville, Maryland
	The pearl that you found is probably a large size for cherrystone clams, but some clam pearls are much larger. The "Pearl of Allah," for example, was an elongate clam pearl 91/2 inches in length. Interesting information about pearls is given in "The Pearl-Gem of the Sea," Sea Frontiers, Vol. 9, No.1, February, 1963.
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	Q&A 13.	We have a 30" x 18" x 7" shell from the South Pacific giant clam. Are there several layers of mother-of-pearl in this shell? Palos Verdes, California
	There is no mother-of-pearl in the shell of the giant clam, Tridacna gigas. Mother-of-pearl is formed of very thin leaves of equal thickness (about 1 micron or less) which are nearly parallel with the shell surface. Shells with prismatic structure do not have it. Mother-of-pearl is made of the mineral aragonite. Most aragonitic shells do not have mother-of-pearl, however, and neither do shells made of calcite, such as the common edible oyster.
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	Q&A 14.	How is pearl essence, also known as fish silver and essence d'orient, recovered from fish scales? Short Hills, New Jersey
	In America, scales from herring, Clupea harengus, are used. As discussed in Marine Products of Commerce by Tressler and Lemon (Reinhold Publishing Company, New York, N.Y., 1951), the shiny material containing guanin crystals is scrubbed off the scales and the wash water is removed, usually by centrifugation. The dried sediment can be purified either by repeated wash- ings with dilute ammonium solutions, which dissolve the epidermis and leave the pearl essence, or by digesting the crude product with pepsin and acetic acid. After the digestion, the guanin crystals are separated from the sludge with ether. They must be washed several times so that all oil and fat, which also enter the ether phase, are washed out. The pearl essence can then be used to coat glass beads for imitation pearls.
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	Q&A 15.	During a visit to Grand Turk. Bahamas, I was shown a pear-shaped, delicate pink object which was reputed to be a conch pearl. Can you provide information about such a pearl? Sayville, New York
	Pink conch pearls are formed by the mantle of the queen conch, Strombus gigas. In the nineteenth century, these pearls cost as much as $5,000 for large specimens. Today, however, conch pearls are valued at no more than $20 to $30, since they eventually lose both their color and luster. On rare occasions, pearls are found in the mantle of other species of marine gastropods. The color of such pearls is more or less the same as that of the glossy interior of the aperture of the particular species. For example, orange pearls have been found in the Florida horse conch, Pleuroploca gigantea.
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	Q&A 16.	Do clams produce pearls? If so, do the pearls have any value? Fort Salonga, New York
	Virtually all bivalved mollusks, including clams, are capable of secreting a calcareous pearl of sorts, but only those species that contain an iridescent, nacre, known as mother-of-pearl, can produce pearls that have commercial value. Clam shells do not contain nacre; hence, their pearls lack luster and are of relatively little value. Pearls resembling white or purple beads are occasion- ally found in the bay quahog, or hard clam (Mercenaria mercenaria), and may bring as much as $35 on the market, according to the Virginia Institute of Marine Science Manne Resource Bulletin, January-February 1977.
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	Q&A 17.	I recently purchased some oysters from Apalachicola, Florida. Upon opening one of the oysters, I found the enclosed seven hard, round objects. Are these pearls? If so, is it rare to find more than one pearl in any oyster? Thomasville, Georgia
	Most mollusks are capable of producing pearls as a mechanism to isolate and "smooth" rough objects trapped in the shell. The number of natural pearls in an animal depends on the individual's ability to expel foreign material from inside the shell. Particles that are not expelled act as the nuclei for forming new pearls. As many as 1,716 pearls have been found in one oyster, according to The Guinness Book of Animal Facts and Feats by Gerald L. Wood (Guinness Superla- tives Ltd., Great Britain, 1982). This specimen was collected by Chinese fishermen off Kwantung province in 1958. Most oysters, however, produce only one to three pearls.
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