pearl mussel (Cristaria plicata). This mussel produced a high volume of low-quality pearls that came to be known as "raisin pearls" in the 1970s and 1980s. More than a decade ago the freshwater pearl industry of China shifted production from the cockscomb pearl mussel to the triangle shell mussel (Hyriopsis cumingii). The triangle shell produced fewer pearls, accepting only 12–16 grafts per valve for a total production of 24 to 32 pearls, but produced pearls of better quality. Processing Freshwater pearl harvests are typically bought while still in the shell. After harvest the pearls are delivered to a first-stage factory, which is responsible for cleaning and sorting the pearls by size and shape. After this process has been completed, the pearls are considered ready material for processing factories. The pearls are pre-treated (maeshori) in a warm and cold chemical solution and then bleached. The pearls that exhibit strong coloration only go through the maeshori and are not bleached or dyed. After the pearls are treated, they are drilled and then polished with a mixture of cornmeal and wax. Finally they are matched into temporary strands, which are then matched again into hanks. Hanks are composed of 5 to 10 temporary strands and are considered wholesale-ready. See also Cultured pearl Fishing industry in China Agriculture in China References Pearls