Pearl culture , Method, Process, composition of pearl

 

The pearls are of variable shapes and sizes. They may be white, or cream red or pink red in colour. The spherical pearls of rainbow colour are rarely found. The best quality of pearl is obtained from marine oysters. Pearl obtained from freshwater bivalves are not as valuable as those obtained.

Pearl comprises of  Water: 2-4%, Organic matter:3.5-5.9%,  Calcium carbonate: 90% residue 0.1 to 0.8%                                                                     

Pearl is a white shining round structure formed  within the shell of an animal called Oyster therefore animal is commonly called as  Pearl oysters. It is  sedentary animals belong to phylum molluscs of class Pelecypoda. High quality pearls are obtained from pearl oysters of Pinctada vulgaris. A Freshwater bivalve millican  Lamellidens is also used in artificial pearl culture. 

Mostly the pearl oysters are found in the ridges of rocks or dead corals and the population of oyster is called  pearl banks. These pearl oysters  produce best quality of pearls called as Lingha Pearl.

How does pearl formation occur

When a foreign particle accidently enters into the space between mantle and shell of the oyster than oyster cling the foreign particle woty its mantle. The mantle epithelium create a sac to enclose the foreign  particle and starts to secrete concentric layers of nacre around it. These concentric layers are made up of calcium carbonate. The secretion of these layer by animal represent  as a defensive mechanism. Nacre is secreted continuously by the mantle and is deposited around the foreign particle and over a period time the formation of repeated layers of calcium carbonate makes the hard and white  pearl.  

When the pearl enlarges the oyster dies. The shell is then carefully opened and the pearls are manually separated and extracted.

The Artificial Insertion of Nucleus is major approach to get pearl in highest number. This can be achieved by an artificial device to insert the nucleus as foreign particle in the shell of oyster has proved useful for the production of pearls in greater number.

Pearl culture 

Oysters are collected by special type of cages which is made up of two centimeter thick of  wire mesh. These cages are suspended at a depth of 6 meters prominently from July to November, where oyster  are easily available. These collected oysters are now transferred to another cages which is used to domestication or rearing of pearl oyster.

The collected oysters are stored in special type of cage called as rearing cage. These cages are well designed and provide  protectetion from enemies of oysters like Octopus, Eel, Devil fishes etc. The collected oysters are first cleaned and then placed to adapted physiological adjustment to the shallow water conditions.

Now a piece of mantle of living oyster is cut off and inserted together with a suitable nucleus inside the living tissue of another oyster. Pearl oyster whose mantle is used to insert with the nucleus must be healthy and strong enough to overcome the stress during operation.

 The piece of tissue which is inserted inside the mantle is called as graft.. The graft must be placed in such a way that it must be in contact with the outer surface of the mantle because   the nacre secreting cells are found only on the outer surface of the mantle. 

 Any small particle may be used as nucleus to initiate the pearl formation but calcareous nucleus is the best because the deposition of nacre was found to be more on calcareous particles.

Nucleated oysters are placed into cages and suspended into sea water up to depth of two  to three metres for about seven  days. This period of seven  days is known as ‘Recovery period’. About three thousand nucleated oysters may be kept in different cages to harvest the pearl. 

 Pearls are harvested in the month of December to February which may slightly vary according to climatic conditions. After the completion of 3 years of the insertion of nucleus, pearl oysters are harvested from the sea and the pearls are taken out from the shell. After taking out the pearls from the oysters shell they are washed properly, cleared with the soap solution

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