Cultured pearl

A newly-opened Hyriopsis cumingi, freshwater mussel, showing the rows of cultured pearls inside.

A cultured pearl is a pearl created by a pearl farmer under controlled conditions.

Development of a pearl

A pearl is formed when the mantle tissue is injured by a parasite, an attack of a fish or another event that damages the external fragile rim of the shell of a molluc shell bivalve or gastropod. In response, the mantle tissue of the mollusk secretes nacre into the pearl sac, a cyst that forms during the healing process. Chemically speaking, this is calcium carbonate and a fibrous protein called conchiolin. As the nacre builds up in layers of minute aragonite tablets, it fills the growing pearl sac and eventually forms a pearl. It is a myth that a grain of sand can cause a pearl to form, as nacre will not adhere to inorganic substances.

Natural pearls are those pearls that are formed in nature, more or less by chance. Cultured pearls, by contrast, are those in which humans take a helping hand. By actually inserting a tissue graft of a donor oyster, a pearl sac forms, and its inner side precipitates calcium carbonate in the form of nacre.

A common pearl “seed” is made from a small piece of the Mississippi pigtoe mussel shell that has been cut and ground in a sphere. The mantle gland is harvested from one oyster and cut into small pieces. The oyster is placed in warm water to relax the oyster, which is gently pried open. A small incision is made and the seed inserted along with a small piece of mantle gland. The oyster is then placed back in the water and allowed over several years to coat the seed with nacre.

The pearl industry

Modern-day cultured pearls are primarily the result of discoveries made in the late 19th and early 20th centuries by the Japanese researchers Mise and Nishikawa. Although some cultures had long been able to artificially stimulate mollusks into producing a type of pearl, the pearls produced in this way were only blister and mabe, rather than actual round pearls. What Mise and Nishikawa discovered was a specific technique for inducing the creation of a round pearl within the gonad of an oyster. This technique was patented by Mikimoto Kōkichi shortly thereafter, and the first harvest of rounds was produced in 1916.

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 for up to two years until each pearl was fully formed, thus better ensuring their health and survival. And the pearls could be produced 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 more than 99% of all pearls sold worldwide are cultured pearls.

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

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