Cultured Pearl - Development of A Pearl

Development of A Pearl

A pearl is formed when the mantle tissue is injured by a parasite, an attack of a fish or another event that damages the external fragile rim of the shell of a mollusk shell bivalve or gastropod. In response, the mantle tissue of the mollusk secretes nacre into the pearl sac, a cyst that forms during the healing process. Chemically speaking, this is calcium carbonate and a fibrous protein called conchiolin. As the nacre builds up in layers of minute aragonite tablets, it fills the growing pearl sac and eventually forms a pearl. It is a myth that a grain of sand or grit can cause a pearl to form, as nacre does not adhere to inorganic substances.

Natural pearls are formed by nature, more or less by chance. On the other hand, cultured pearls are human creations formed by inserting a tissue graft from a donor oyster, upon which a pearl sac forms, and the inner side precipitates calcium carbonate in the form of nacre.

A common pearl “seed” is made from a small piece of the Mississippi pigtoe mussel shell that has been cut and ground in a sphere. The mantle gland is harvested from one oyster and cut into small pieces. The oyster is placed in warm water to relax the oyster, which is gently pried open. A small incision is made and the seed inserted along with a small piece of mantle gland. The oyster is then placed back in the water and allowed over several years to coat the seed with nacre. The parasite is coated in many layers of this nacre, so that if pearls are sawed in half, visible layers can be seen.