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(Nature´s response to an aggression)
Pearls are formed when an irritating object penetrates by accident inside the shell of certain oysters. If the mollusc in question cannot expel it, it will isolate the object by means of a substance called "conchiolin", and by depositing layers of calcium carbonate on it (in the form of microscopic crystals of calcite or aragonite). The result is a rounded object covered by a most delicate nacre thickness. A PEARL.
Since ancient times, they have been considered as precious stones and have been widely sought. They have also been part of the treasures belonging to the major royal houses and jewel collectors, such as the Medici in Florence. Pearls used to be extremely expensive because of their scarcity and the danger pearl hunting involved when carried out in the open sea. Therefore, Carolus Linnaeus, in the 18th c. tried to make pearls grow inside oysters. He failed because he introduced a lead ball through a small hole on the oyster’s shell. Naturally enough, oysters died after pearls were extracted.
CULTURED PEARLS
A few centuries later, at the same time and place (Japan), two similar culture systems were developed. Both consisted in introducing a nacre bead in the so-called "Akoya" oysters. One of the systems was patented in 1896 by Kohichi Mikimoto. The other one was invented by Tatsihei Mise and Tohichi Nishikawa. The conflict that emerged between the two competing families was efficiently solved "the Japanese way" i.e., by letting their offspring be married. From that moment on, the production of CULTURED pearls started to develop further on to the high scale. In the 30s, it was already too late for anyone to stop their pervading ubiquity in the jewellery market. Everywhere around the globe, in every woman’s jewellery box, a cultured pearl necklace was never missing. The Japanese have made a point of preserving their traditional high-quality cultured "Akoya" pearls.
FRESHWATER PEARLS
In the 60s, research was undertaken in Japan to try and culture pearl-producing molluscs in freshwater. They managed to do this in the lake Biwa by inserting a small scrap of mantle tissue from another mollusc instead of a nacre bead. This organic nucleus became progressively covered by layers of nacre and was reabsorbed little by little. The final result were "solid" pearls i.e., pearls with a nucleus that was one with the external surface. These pearls were also known as BIWA pearls, and reached very high prices. They were the direct foregoers of FRESHWATER PEARLS, which were cultured in molluscs similar to large mussels with nacre nuclei.
Their production has expanded on the high scale in China, and they are now a major competitor for sea-cultured pearls. Freshwater pearls are very attractive with a variety of shades that range from the silvery to the rose, cream, grey, and white, and may come in a number of shapes different to the classical sphere.
AUSTRALIAN PEARLS
The large oysters in the South Sea also produce pearls of a big size and an excellent quality which have been "cultured" as well.
WHITE pearls are found in Australia, Burma, and in most of the Indian Ocean. The "Pinctada maxima" is the oyster that bears these pearls. Another variety is the BLACK pearl. It is found in the French Polynesia and Tahiti, and it is produced by the "Pinctada Margaritifera" var. cumingi. Both types are characterized by their large size (around 10-14 mm ø) and their slightly metallic colour, and most especially by their parallel growth rings which look very much like "love handles".
They are spectacularly beautiful and have a great quality. Their price is quite high, but it is possible that future improvements in culture techniques (even by means of genetic engineering) may help increase their production.