Freshwater pearls grow in a mussel species (Hyriopsis Schlegeli). The mussels are not rare and are mainly found in rivers, lakes and ponds in China and Japan, and also in Europe, Russia and America. They are propagated in water tanks and ponds.
Biwa freshwater pearls were cultivated in Lake Biwa in Japan from 1914 to the mid 1970's. Biwa was one of the first freshwater culturing sites and pearls from this area were noted for their high quality. However, production has now stopped due to pollution problems, and also because of competition from cheap Chinese production. The Chinese first produced a rice-shaped inferior quality, then step by step improved production to create better quality and smoother surfaces. Cost of labour is very low in China and this put the Biwa producers out of business.
There are only a small number of oysters seeded with nuclei. Most pearls are obtained by simply grafting a number of mantle tissues from another mollusk. Pearl sacs then form around the mantle, which will eventually disappear. The pearl then grows up to any possible size, depending on the number of years the oyster is left in water. In this case, the pearl produced has no nucleus inside. A Freshwater mussel can produce up to 50 pearls at a time.
China now produces Freshwater pearls in enormous volumes (close to 700 tons per year). It takes approximately three to four years to reach the size of 7mm. For larger pearls, the farmer has to wait even longer. After harvesting the pearls, the mussel is placed back into its environment without a new grafting and will produce pearls again in a few years.
Almost all Freshwater pearls are cultivated. Non-cultivated Freshwater pearls are very uncommon.
Freshwater pearls have an endless variety of shapes, sizes and colours from lilac to purple, orange, brown, rose, grey, gold, champagne and white. It is simply a question of taste.