Jewellery is generally designed using precious metals and jewels which are buried in the earth, on the other hand pearls are found inside a living creature, oyster. The pearls are the results of biological process. Pearls are formed in the process of the oyster protecting itself from the foreign substances. The formation of pearl is not an overnight process, but it takes good amount of time.
Oysters are prime produces of pearls, though other mollusks like clams and mussels produce pearls this is very rare. Oysters have two shells. Each shell has a protective layer called mantle, and it is responsible for safeguarding vital organs of oyster.
Natural pearl formation
The main principal behind the formation of pearl in a pearl oyster is the presence of a nucleus. It can be of organic or inorganic origin, such as parasites adults or larvae, molluscan eggs, decaying parts of plants, sand grains, epithelium or blood cells of the same animal, etc. These tiny particles or organisms enter the oyster when the shell valves are open for feeding and respiration. These foreign bodies may become embedded between the shell and mantle. In response, the foreign body is invaginated by the outer epithelium of the mantle and a pearl-sac is formed around it.
The pearl-sac is derived from the internal or external layer of the epithelium of the mantle or of the gill plates. The epithelial cells of the pearl-sac secrets the nacre which becomes deposited over the foreign body, forming a pearl in due course of time. These pearls are produced either within the mantle, in other soft tissues of the oyster, or between the mantle, and the interior surface of the shell. Such natural pearl production is accidental and occurs very rarely.
Artificial pearl formation
Two requirements for pearl formation are outer epithelium of mantle lobe and core substance/nucleus. In artificial production, pieces of mantle form a sacrificed oyster provide the pearl secreting cells whereas processed beads act as the foreign body nucleus. The mantel piece graft tissue and the shell bead nucleus are implanted together into the gonad of the oyster.
The oysters are then returned to sea for further growth. The outer epithelial cells of the graft tissue proliferate and rearrange themselves over the shell bead nucleus, forming a pearl-sac. The inner epithelium and connective tissue of the mantle disintegrate and become absorbed by the surrounding tissue. The cells of the pearl-sac derive their nourishment from the surrounding tissues and soon assume their function of nacre secretion which is deposited over the nucleus in the form of concentric micro-layers. In cultured pearls the nacre quality and the process of pearl formation are the same as in the formation of natural pearls.
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