Cultured freshwater pearls are pearls that are farmed and created using freshwater mussels. These pearls are produced in Japan and the United States on a limited scale, but are now almost exclusively produced in China. It is required by law that farmed freshwater pearls be referred to as “freshwater cultured pearls” in commerce. Quality of cultured freshwater pearls is evaluated through a grading system of a series of A values, based on luster, shape, and other factors.
Pearls gathered in the wild from the Holarctic freshwater pearl mussel were important sources of pearls for medieval jewelry, with Scotland a major source; this species is now endangered in most areas.
Although the Japanese freshwater pearl industry has nearly ceased to exist, it has a special historic place as the first country to cultivate whole freshwater pearls.
The grafting process begins by choosing a suitable donor mussel and cutting a strip of tissue from the mantle. This strip of tissue is then cut into three-millimetre squares. These squares are delivered to a technician who performs the operation.