Among the cultured pearls, the most known and used are definitely Akoya pearls, produced for the first time in Japan and, for more than a century, unique among those cultivated. The diameter of these pearls range from 2 to 9 mm, with peaks of 10 for those of particular value and rarity. They are obtained by the introduction of specific nuclei within the Akoya oyster, which is found in abundance in the temperate eastern sea country. The natural color of these is the cream or yellow-green but with appropriate treatments you can get white, champagne, silver and pink. Also the forms may be changing, although the most common are those spherical. In some cases, you can get the twin pearls, since it is not uncommon to introduce two or more nuclei within the same shell. Over 90% of cultured pearls on the market belong to this variety.