Pearls have been found in a variety of mollusks. In the gem and jewelry trade, the two main pearl producers are the pearl oyster, which is a marine oyster and produces the oriental pearl, and the pearl mussel, a fresh water mollusk producing the fresh water pearl.
PEARLS: Pearls are natural formations secreted in certain mollusk’s interior in response to the accidental intrusion of an irritant (eg. shell fragment) without the aid of human agency. They are composed of concentric layers of conchiolin (an organic substance related to hair) and aragonite, which is a specific crystalline form of calcium carbonate. These concentric layers are called nacre. Light interacts optically with the both the nacre of pearls and the nacre of the mother-of-pearl surface inside the mollusk shell to produce an iridescent sheen called orient. The orient is dependent on the number, quality and thickness of nacreous layers.
CULTURED PEARLS: Cultured pearls are formed the same way as a natural pearl except the irritant (a piece of mollusk mantle tissue or a shell bead called a nucleus together with mantle) is planted in the mollusk interior by human agency. Today, all pearls are cultured as natural pearl occurrence is too rare and harvesting too expensive to be practical.
IMITATION PEARLS: Imitation pearls are not produced by mollusks and possess few characteristics associated with pearls and, therefore, are not pearls.They are simulants manufactured from materials resembling pearls.
FRESHWATER PEARLS: Culturing is done on the bottom of rivers and lakes. These tend to be less valuable than saltwater pearls because the nacre is usually less uniform but they are available in a broader range and more vivid colors than saltwater pearls. Japanese Biwa (lake Biwa where the hyriopsis schlegi mussel thrives) pearls tend to be more valued than freshwater pearls cultured in other countries. China has become the major source of freshwater pearls. China has made tremendous strides in producing almost round to round, large and higher luster, tissue nucleated (no bead) 100% nacre freshwater pearls. In some countries there is culturing of freshwater pearls in clams.
Shapes: Round, near round, semi round, oval, drop baroque, button and coin.
SALTWATER PEARLS: Any pearl produced by mollusks in a saltwater environment. Culturing is done in gulfs and bays. There are three (3) major types, Akoya, Pearls, Black Pearls, South Sea Pearls, each type produced by a different oyster, each type having a different range of sizes and each type being cultured in a different geographical area (some overlapping geography exists).
ABALONE PEARLS: Colored baroque pearls produced by an edible ear-shaped mollusk prized for its multicolored mother-of-pearl lining. These are found in American, Japanese and New Zealand waters. Seldom spheroid, they are usually flattened and ear or tooth-shaped.
AKOYA PEARLS: Saltwater pearls produced by the Akoya Oyster, the Japanese name for a specific type of oyster (pinctada martensii) that flourishes in Japanese waters and produces beautiful pearls. Cultured in Japan and now China and new locations, these are the smallest of the three major types of saltwater pearls and typically range in size from 2mm to 11mm, are round or off-round and more or less white or cream, light yellow, white or cream body color with pinkish, deep rose or green overtone, silver and more rarely yellow, pink or blue
Shapes: Round, near round, semi baroque and baroque.
BAROQUE PEARLS: Name applied to any type of pearl with an irregular shape.
BLACK (“TAHITIAN”) PEARLS: Dark colored saltwater pearls whose color is natural and have a typical size range of 8mm to 16mm which is intermediate between Akoya and South Sea Pearls. Produced by the black-lipped oyster ( pinctada margaritifera) in waters along the Tropic of Capricorn from the Indian Ocean to French Polynesia. Black Pearls have become commercially important in the last thirty years. Colors: Silver gray, gray, black, bronze, dark blue, blue-green, green. Some have overtones: green and magenta (peacock), reddish purple with green (eggplant),
Shape: Round, near round, oval, drop, semi baroque, baroque, circle.
BLISTER PEARLS: Pearls, which are covered on one side only by a nacreous layer due to formation over an irritant on the surface of the interior mollusk shell. The side lacking nacre is typically smoothed and hidden by the jewelry setting.
CONCH PEARLS: (“PINK PEARLS”): Produced by the Great Conch, a mollusk found off the coast of Florida and the Gulfs of California and Mexico. Normally pink, pinkish orange or pinkish white, they lack a nacreous coating and vitreous porcelain-like surface with flame-like markings.
CYST PEARLS: Any pearl formed in the pearl mollusk body and which is spheroid in shape.
KESHI PEARLS (saltwater): Japanese name for Seed Pearls; they are naturally formed. “Keshi” translates to poppy; the association being the tiny seeds of the poppy flower.
KESHI CULTURED PEARLS (freshwater): Naturally occurring non-nucleated pearls which form in a mollusk when it is returned to the water after removal of a crop of non-nucleated pearls. Normally having a flat baroque shape they can vary in size.
MABE PEARLS: A variety of Blister Pearl produced by the Black Winged Oyster (pteria penguin) in saltwater off the Japanese coast. This oyster can only produce blister pearls, 5 to 8 at a time and which have a luster of the highest quality.
MABE ASSEMBLED PEARL: A Mabe Blister Pearl which has had the non-nacreous side scooped out and replaced with a man-made filling (e.g., plastic) for improved durability.
MELO PEARLS: Produced by the Melo Melo Conch in Southeast Asia and Northern Australian waters. Colors are pale yellow to deep orange and, like the Conch Pearl, they are non-nacreous with a porcelain-like surface with flame-like markings.
SEED PEARLS: Any pearls that are less than ¼ grain weight (1 pearl grain=0.25 carat). They are usually unsymmetrical.
SIZE OF PEARLS: The size of a single cultured pearl is expressed in terms of diameter, expressed in millimeters. The size of any natural pearl is expressed in grains (1grain=0.25carat).
SOUTH SEA PEARLS: These are the largest of saltwater pearls with a diameter range of 9mm - 20 mm and are white, silver or yellow to yellow orange in color. Some have overtones of champagne, rose, green and blue. Yellow to yellow orange are cultured in the gold lipped oyster. Whites and silvers are cultured in the large Silver-lipped oyster (pinctada maxima). These oysters flourish in waters stretching from Burma, Indonesia down to Australia and French Polynesia. These big pearls earned the name South Sea because they were originally produced by the Japanese in Micronesia and Indonesia. Today, the largest production is in Australia. Burma (Myanmar), Indonesia, the Philippines, Papua New Guinea and Thailand are less important sources.
Shapes: Round, near round, drop, oval, semi baroque, baroque, circle.
PEARLS THAT HAVE BEEN STRUNG:
Pearl Strand: Round pearls that have been drilled and are on a string. Pearl Necklace: A pearl strand with a clasp. Uniform Strand: All the pearls are of approximately the same size (6 ½ -7mm is common) Graduated Strand: Pearls are of increasing size towards the center of the strand. Choker: 14 inches – 16 inches. Princess: 16+ inches – 20 inches. Matinee: 20+ inches – 26 inches. Opera: 28 inches – 32 inches. Rope: Longer than Opera size strand.
CARE OF PEARLS:
Although pearls are reasonably tough, it must be considered that they are soft and are made of calcium carbonate and, as such, can be scratched by abrasive materials and attacked by certain chemicals. Hair spray, vinegar, perfume, perspiration and some cosmetics will attack pearls. Also prolonged exposure to excessive heat can cause discoloration, drying out and cracking.
Pearls are usually knotted between each bead, not only because it protects them and holds them in proper spacing, but also because in the event of the thread eventually breaking, the knots prevent the pearls from being scattered and lost. Pearls should be re-strung once a year if regularly worn.
CLEANING:
Pearls will keep their luster better if wiped clean with a soft cloth (dry or damp), after wear, to protect them from perspiration.
Avoid detergents, baking soda and ammonia-based cleaners. Never clean pearls in ultrasonic cleaners. Never steam clean pearls. Do not use toothbrushes, scouring pads or abrasive materials.
Pearls can be washed in mild soapy water, such as Ivory soap, and cleaned with a soft cloth. If one of the prepared pearl cleaners on the market is used, be sure that the strand is rinsed thoroughly in warm water before gently wiping dry with a soft cloth. After washing, the pearls should be laid flat on a moist kitchen towel to dry. After the towel is dry the pearls should be dry. Never hang pearls to dry as a wet thread is inclined to stretch; if so, a restringing job will be necessary. Wiping pearls with a few drops of olive oil on a chamois will restore their brilliance and prevent them from drying out (pearls contain about 2 to 4% water).
STORING:
Pearls should not be stored near heaters or in direct sunlight. Do not store pearls where they might rub against harder substances. It is a good idea to keep pearls in individual flannel/silk bags, satin-lined jewel box, or the like (never in cotton wool). Safe deposit boxes can be unusually dry, and if pearls are stored there, they should occasionally be taken out and exposed to humidity and moisture.
Pearl Strand: Round pearls that have been drilled and are on a string.