Pearl production in the pearl mussels, because there are foreign objects into the outer coat membrane of the clam, the clam itself is stimulated, but it can not be excluded, it will secrete calcium carbonate and true mother-of-pearl to encapsulate it, about three or four times a day secretion, each time covering the thickness of the coating is only 0.5 microns, and it takes more than two years to grow into a gem-level quality pearls. The longer it takes, the more the pearl mussels secrete layer upon layer of nacreous material to cover it, and the larger the pearl becomes. But this is not unlimited, the size of the pearl formation, but also by the cultivation environment, the health of the pearl mussels, some pearl mussels will be not adapted to the early protrusion of pearls and so on. Different pearl mussels of different sizes, the size of the pearl can bear is also a different limit.