Pearl

Pearls - the only jewelry materials produced in the body of mollusks, and he is, perhaps, one of the oldest stones used for decoration because they do not require additional treatment. For many centuries, high-quality pearls sold for exorbitant prices, but with the arrival on the market of cultured pearls in the 1920-1930's of this price leading to an end.
The formation of a pearl in an oyster clam bags is a reaction to the presence of particles of irritating him. Clam series wraps its layers of crystals of aragonite (calcium carbonate), and fastened together with organic matter, konhialinom. The layers build up, like a bulb, and there is a gem. Aragonite crystals are placed in the same order as the shingles on the roof - hence the unique pearl luster.
In cultured pearl serves as the core of the bead, which lays clam layers of natural nacre. The best method for identification of cultured pearls is to check the X-rays - is perfectly visible beneath the bead core (see photo 56). A good layer of natural pearls cultured pearl is thick enough, the same low-quality, it's just a thin film on the surface of the beads. We had to handle a necklace of cultured pearls with a thin layer of nacre, the beads under him were clearly visible. The thickness of the nacreous layer of cultured pearls can range from about 0.5 mm to 3 mm.
I must say that the man who once studied the pearl begins to understand the variety, the most important when working with natural samples. Pearl should have good color and luster, and the best pearls - pink color, and his "skin" should be as smooth as possible, intact. Low-quality color cultured pearls are usually wax on the surface of visible defects, similar to the following form to fill. The better the color and luster, the higher the cost of a pearl. Big natural gems of good color, shiny, smooth and correct form, is still extremely expensive. This gem of more than 10 mm in diameter is considered a rare and highly valued. Even necklaces of cultured pearls in the auction can cost over a million dollars.
"Baroque" gems and pearls of irregular shape, cultured or natural, are much less round and the correct form of the samples. "Blister" gems cut from the clam shell, so they take the shape cabochon. Two blister pearls, fastened together, can simulate a large round pearl, if the line of glue to mask the rim. Pearls "Jap" or "Mabe" also blister, and their core is the drive, the cost of any small blister pearls.
"Imitation" of pearls are usually glass beads, which layer of the "Eastern essences", extracted from fish scales, or hollow beads coated with the same substance inside. To check in this case, you can rub the old gem on the front teeth, with natural or artificial pearl will be a little rough, and the simulation will be smooth.
Pink pearl-like coral, shells and grow in different characteristic "ognepodobnym" pattern on the surface, visible with a magnifying glass, and silver glitter. The best of them can cost up to several thousand pounds.
Freshwater pearls have much less brilliance, it can be found in jewelry XIX - early XX century, usually pearls extracted from the River Tay
in Scotland, and from the Mississippi to the U.S.. Nuclear-free cultured pearls produced in the river farms in Japan, and more recently - in China, in large quantities, such gems weigh less than conventional cultured samples are whiter, but they can be custom painted, their shape more oval. Once you see, then they are easy to distinguish, their cost is low.
Natural "black" pearls are rare and highly valued. Cultured pearls are sometimes stained with silver nitrate, making it look like the black, but this induced color is darker and homogeneous. There are ways to grow cultured black pearls, and if it reaches a significant sample size, and their cost can be high.
In determining the quality of pearl lover is best to contact a reputable gemological laboratory, X-ray equipment where there is, in addition, buying an expensive pearl buyer may request the seller a certificate confirming its origin.