Natural freshwater pearls occur in mussels just as saltwater pearls occur in oysters. A foreign object enters or is entered into a mussel and is not expelled creating a cultured freshwater pearl. The irritant is covered with nacre.
Japan cultured the first freshwater pearls with freshwater mussels. They were the first to culture pearls in freshwater mussels in Lake Biwa, a large lake near Kyoto. It first started in the 1930’s. These Biwa pearls formed in colors “unseen in saltwater pearls”. They rivaled natural pearls because of “their luster and luminescent depth”. In 1984, the shores around Lake Biwa were getting polluted because of development around the lake and pearl farming was barely surviving. Production began in China where there were countless rivers, lakes and irrigation ditches to produce pearls.
In 1968, China introduced inexpensive pearls to the world market. In the 1970’s and 1980’s, the pearls did not compare to the Japanese pearls. The Chinese pearls had a “crinkly” surface and were dyed in popular color.
Between 1984 and 1991, China produced better shaped and colored pearls. In 1990, China had learned enough to produce pearls with even better shape, luster and color than the Biwa quality pearls. In fact, they were round enough to compare to the Japanese Akoya.
“The Chinese are nucleating mussels with their own tissue-cultured fresh water pearls, which result in all-nacre round or almost round pearls”. They are also reshaping reject freshwater pearls into a round shape and then nucleating mussels with them.