are created by a human implanting foreign matter such as a bead nucleus and/or a small square of donor tissue into a mollusk
. Pearls are formed when mollusks secrete nacre, a substance that layers over this implant in their gonads or pearl sacs. This nacre, a combination of calcium carbonate and conchiolin, builds up over the course of two or more years.
In Japan, the researcher Mikimoto refined a technique to produce round and near-round Pearls. Up until this time most cultured Pearl products were what is called mabe
, or half-spheres that were formed when a disc was adhered against the inside of the shell. Now, with the bead nucleus and the additional help of the donor tissue, better-shaped Pearls could be formed in a regular fashion, which led to greater production.
From the wild Pearls, which varied considerably in shape, color and size, to the new, more consistently shaped and sized round Pearls, the Pearl industry was on its way to producing Pearls in such vast numbers that they became very affordable.
Now cultured Pearls are produced around the world - in China, the South Seas, New Zealand, Australia, Southeast Asia, and in many other countries. Freshwater Pearls are grown in mussels. Baroque, oddly-shaped pearls, are grown in seawater in the bodies of abalone or oysters. Many other types of Pearls are harvested from particular species of mollusks that produce Pearls of varying colors and overtones, shapes and sizes.
Two distinct types of cultured Pearls are the beaded cultured Pearls – Akoya from the South Seas and Tahiti, which are grown one at a time in the gonads of the oysters – and non-beaded freshwater cultured Pearls – as in Biwa or Chinese Pearls. These latter Pearls are grown in the mantle of the mussel and many at one time are inserted, leading to a greater proliferation and lower cost.
The best way to tell the difference between a natural and a cultured Pearl is through x-raying it, which means the nucleus can be distinguished. Since ninety-nine percent of the Pearls sold today are cultured, the likelihood of finding natural Pearl jewelry is decreasing.