A pearl is formed when some sort of small object, typically a parasite or piece of organic matter, becomes embedded in the tissue of an oyster or mollusk.

In response, the mantle tissue of 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.

Cultured pearls, by contrast, are those in which humans take 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 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 Kokichi Mikimoto 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 is 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. Led by pearl pioneer John Latendresse, the United States began culturing freshwater pearls in the mid 1960's.

In Palm Island, Queensland, Australia in 2004, in a now closed pearl farm, pearl oysters commenced life as spats from hatchery farms, and were then grown for two years on a pearl farm. They were then seeded as pearls and cultivated for another two years, suspended on long lines, some on the surface, others below the surface. Each line had vertical lines dropping from it at one metre intervals with about six to eight shells on each vertical line. When the pearl had grown, two to three years after seeding, it was removed and the shell was reseeded to produce a second, bigger, pearl. Shells had a commercial production life of 10 to 12 years, producing roughly every two years.[1]

Prior to the 1930s, exporting pearls was the main economic activity of Kuwait. When the Japanese invented cultured pearls, the Kuwaiti pearl market declined. It would not be until World War II that oil became the major export for Kuwait.

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

Today more than 99% of all pearls sold worldwide are cultured pearls.