Towards the end of the 19th century, the value of natural pearls grew to such an extent that various species of mollusc were nearly driven to extinction. It was about this time that Kokichi Mikimoto, a Japanese entrepreneur, was successful in raising pearl-producing oysters, culturing these greatly desired jewels and commercialising them. He took the spherical pearl culturing methods developed by an English marine biologist, William Saville-Kent – a little later patented by Tatsuhei Mise and Tokichi Nishikawa – and adapted them for large-scale exploitation.
Cultured and natural pearls essentially share the same origins. To create a cultured pearl, nature is simply given a helping hand. Instead of waiting for some foreign object to enter the mollusc, a section of mantle tissue is transplanted into a host-mollusc, with or without the simultaneous implantation of a nucleus. The mantle is the soft outer tissue of the donor mollusc and the nucleus is a piece of shell rounded into the shape of a bead. The host mollusc is then returned to the water, suspended on pearl rafts, where it is left to grow gradually until the pearl reaches its ultimate size. For salt-water pearls this usually takes between one and three years; fresh water pearls, however, may remain in the water for significantly longer. During this time the molluscs are tended by pearl farmers. Even though they are carefully protected, molluscs often fall prey to whims of nature such as typhoons, predators, insufficient water quality and disease.
See also the video presentation: Computer tomography of pearls
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