A pearl is formed when some sort of small object or irritant becomes embedded in the tissue of an oyster or mollusk. In response, the mollusk secretes nacre, a combination of crystalline and organic substances. As the nacre builds up in layers, it surrounds the irritant and eventually forms a pearl.

Natural pearls are those pearls which are formed in nature, more or less by chance, by a parasite or a piece of food lodging itself in the gonad or mantle tissue of a host oyster. Cultured pearls, by contrast, are those in which humans give a helping hand. By actually inserting a foreign object into the tissue of an oyster or mollusk, pearl farmers can induce the creation of a pearl. The same natural process of pearl creation takes place. The only difference is that in the one case, the process was begun accidentally; while in the other case, it was begun intentionally.

Modern-day cultured pearls are primarily the result of discoveries made in the late 19th and early 20th centuries by Japanese researchers, most notably Kokichi Mikimoto. Although some cultures had long been able to artificially stimulate freshwater mollusks into producing a type of pearl, the pearls produced in this way were generally hemispherical mabes*, rather than actual round pearls. What Mikimoto discovered was a specific technique for inducing the creation of a round pearl within the tissue of an oyster. This discovery revolutionized the pearl industry, because it allowed pearl farmers to reliably cultivate large numbers of high-quality pearls. In contrast to natural pearls -- which have widely varying shapes, sizes, and qualities, and which are difficult to find -- cultured pearls could be "designed" from the start to be round and primarily flawless. The oysters could be monitored during the several years required for each pearl to become fully formed, thus better insuring their health and survival. And the pearls could be grown by the tens of thousands, thereby bringing their cost down to a point where pearls became accessible to large numbers of people around the world.

In short, the development of cultured pearls took much of the chance, risk, and guesswork out of the pearl industry, allowing it to become stable and predictable, and fostering its rapid growth over the past 100 years. Today the cultured pearl industry has effectively replaced the natural pearl industry, turning the natural gems of old into collectors' pieces.

Cultured pearls can often be distinguished from natural pearls through the use of x-rays, which reveals the inner nucleus of the pearl.

mabes* - A mabe is a hemispherically shaped pearl which is grown against the inside of the oyster's shell, rather than within its tissue. Mabes occasionally appear in nature. Cultured mabes are grown intentionally, by using a hemispheric nucleus, rather than a round one; and by implanting it against the oyster's shell, rather than within its tissue. The pearl then develops in a hemispheric form, with a flat back. While in the oyster a mabe pearl is actually considered a blister pearl not a mabe pearl. After the blister pearl has been 'worked' it then becomes a mabe pearl.Blister pearls are worked by cutting the pearl out of the shell with a circle-bit drill. The nucleus is then removed and replaced with a resin.The back of the pearl is capped with a piece of mother-of-pearl to complete the mabe pearl.Cultured mabes are used for such things as rings and earrings, rather than for stringing on necklaces. They tend to be very beautiful with high luster and orient, but are priced much lower than round pearls.

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