Pearl is a natural gem and is produced by a mollusc. The pearl is both mystic and beautiful with its soft colour and cool luster. While the demand of pearls in India and elsewhere is increasing, their supplies from nature have reduced due to over exploitation and pollution. India is importing a large amount of cultured pearls every year from international market to meet the domestic demand.
Scientifically a pearl can be defined in three ways. In simple chemical language, the composition of a pearl is about 82-86% aragonite crystals of calcium carbonate;10 to 14% organic matrix, a scleroprotein termed as concholin and 2 -4% water. In physical terms, a pearl has 3.5 to 4.5 hardness on Moh’s scale with a specific gravity of 2.7. Biologically, a pearl is more or less similar to the inner shining layer called ‘mother of pearl layer' or nacre of shells.
In nature, a pearl is formed when a foreign particle viz., piece of sand, insects, etc. by chance enters into the body of mussel and the mussel can not reject that out and instead makes a shiny coating on the particle layer by layer. This simple phenomenon is being exploited in pearl culture practices.
Pearl are produced by certain oysters in the marine and some mussels in the freshwater environments. The pearls available in the market could be broadly classified into three types - artificial, natural or cultured.
Artificial or imitation pearls are not pearls but pearl-like materials that simply contain a rigid, round core or base and an outer pearly coating. The coating can vary from inexpensive shining paints to synthetic pearl essences to natural essences obtained from certain fish scales.
Majority of imitation pearl give smooth feeling when rubbed against teeth and when a pin is pressed into the surface,it easily leaves a scratch or indent unlike genuine natural or cultured pearls.
The core or nucleus of the natural pearl is minute with fairly thick crystalline pearl nacre. Generally a natural pearl is small in size and irregular in shape.The surface of a natural pearl gives a rough feeling which is due to the edges of the overlapping crystals of aragonite. This is a very useful character in determining the genuineness of a pearl.
When a foreign matter, sand, small s tone or creatures are trapped between the outer shell and the body or any other part, in order to avoid the unbearable pressure the nacre cells membrane will start to .grow on the foreign body. The aragonated secretion (a form of calcium carbonate) produced by the nacre cells will cover the foreign body and later transformed into pearl.The shape of the pearl will depend upon the foreign body trapped inside. If it is trapped between the outer shell and mantle it will be shapeless and flat and have pearl cover only on one side. If it is inside the flesh the pearl will be round. The pearl is a precious creation and blessing of nature.
A cultured pearl is also a natural pearl, the only difference being the human intervention in surgical implantation of a live mantle graft and nucleus for hastening pearl formation to the desired size,shape, colour, and lustre. In India, three species of commonly available freshwater mussels viz., Lamellidens marginalis, L. corrianus and Parreysia corrugata are found to produce good quality pearls.
Design cultured pearls
When images designed by man is intentionally placed between the mantle and outer cover of the shell, to avoid unbearable pressure nacre cells will start growing around the foreign matter (cab). Gradually the cab will transform into pearl. In one way it is a natural pearl only. Only thing is that it is not accidental but due to human intervention. This design-cultured pearl will stay as the symbol of beauty forever. Only upper part of the bead will have pearl covering and when it covers completely the remaining part is cut from the outer shell. The cab inside the removed part is removed and a special type of cement is filled in place. This type of pearl is used in necklace and earrings and will certainly increase the beauty of the wearer. In Bristol pearl one side is flat. If the pearl have any other design instead of hemisphere it can be called as a design pearl. The colour of the pearl will depend on the food given and the type of mussel. Usually pearl made from fresh water shells are seen in pure white, cream, pink, green, steel grey, gold rose and peacock blue.
Source : Mr Ravikiran Bhat, Karnataka
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