Chinese freshwater pearl oysters can be harvested anywhere from 2 years to 6 years after nucleation. Each mussel is normally nucleated with 40 to 50 tissue implants at nucleation, and of these usually about 30 to 40 cultured pearls are yielded. Most freshwater pearl harvests take place in November, just before winter begins. Some of the harvested mussels, if they produced good quality cultured pearls, are returned to the water with hopes that a second generation of cultured Freshwater Pearls are on the way. The pearl sac in these mussels is already formed, and therefore no more insertion of mantle tissue is required. The second generation of freshwater cultured pearls is generally not as good quality as the first.
There are dozens of colors from Chinese freshwater pearls, including white, ivory, yellow, orange, and purple. They are usually sorted by size, shape, and color by processors in China. They are put in jars along with a bleach solution, and put in a room flooded with fluorescent light. One to two months later, the pearls are removed and air dried. They are then mixed with small pieces of vegetable grit, bamboo, wood, or walnut shells, and tumbled in specially designed machines.
Of the harvested pearls, only about 2% are usually round or near round. Because the Chinese produce so many freshwater cultured pearls, there is still a large quantity coming out of the harvests in any given year. 2% of 675 metric tons of cultured freshwater pearls will yield about 13,500 kg of round or near round freshwater cultured pearls.
Many farmers believe that round or near-round cultured pearls occur strictly by chance. They still do, however, try to improve their chances by using preferred mussel species, allowing a longer growth period, improving water quality, etc. Anything that could yield even 0.5% more round, high quality pearls is worth trying as round pearl necklaces are more highly valued than other shapes used in pearl jewelry.