A great irony of pearl history is that the least expensive cultured pearl product in the market today rivals the quality of the most expensive natural pearls ever found. The price-value anomaly is obvious to consumers as they hasten to buy Chinese freshwater bargains. Indeed, pearls from freshwater mussels lie at the center of the liveliest activity in pearling today. Natural freshwater pearls occur in mussels for the same reason that saltwater pearls occur in oysters. Foreign material, usually a sharp object or parasite, enters a mussel and cannot be expelled. To reduce irritation, the mollusk coats the intruder with the same secretion it uses for shell-building, nacre. To culture freshwater mussels, workers slightly open their shells, cut small slits into the mantle tissue inside both shells, and insert small pieces of live mantle tissue from another mussel into those slits. In freshwater mussels that insertion alone is sufficient to start nacre production. Most cultured freshwater pearls are composed entirely of nacre, just like their natural freshwater and natural saltwater counterparts.

The Chinese were the first to culture a product from freshwater mussels, though their centuries-old Buddhas are not true pearls but shell mabes. The first cultured freshwater pearls originated in Japan. Quite soon after their initial success with cultured saltwater pearls, Japanese pearl farmers experimented with freshwater mussels in Lake Biwa, a large lake near Kyoto. Initial commercial freshwater pearl crops appeared in the 1930s. The all-nacre Biwa pearls formed in colors unseen in saltwater pearls. Almost instantly appealing, their lustre and luminescent depth rivaled naturals because they, too, were pearls through