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For other things called "pearl", see pearl (disambiguation).
Physical Description
Japanese pearl diver
A pearl is a hard, rounded object produced by certain mollusks, primarily oysters. Pearl is valued as a gemstone and is cultivated or harvested for jewellery.
Pearls are formed inside the shell of certain bivalve mollusks. As a response to an irritating object inside its shell, the mollusk will deposit layers of calcium carbonate (CaCO3) in the form of the minerals aragonite or calcite (both crystalline forms of calcium carbonate) held together by an organic horn-like compound called conchiolin. This combination of calcium carbonate and conchiolin is called nacre.
The unique luster of pearls depends upon the reflection and refraction of light from the translucent layers and is finer in proportion as the layers become thinner and more numerous. The iridescence that some pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. Pearls are usually white, sometimes with a creamy or pinkish tinge, but may be tinted with yellow, green, blue, brown, or black. Black pearls are often highly valued because of their rarity.
Pearl farm, Seram, Indonesia
History
Before the beginning of the 20th Century, pearl hunting was the most common way of harvesting pearls. Divers manually pulled oysters from ocean floors and river bottoms and checked them individually for pearls. Now, however, almost all pearls used for jewellery are cultured by planting a core or nucleus into Pearl Oysters. The pearls are usually harvested two years after the planting. This mariculture process was first developed by Kokichi Mikimoto from Japan, who was granted a patent for the process in 1896. The nucleus is generally a polished bead made from mussel shell. Along with a small scrap of mantle tissue from another oyster to serve as an irritant, it is surgically implanted near the oyster's genitals. Oysters which survive the subsequent surgery to remove the finished pearl are often implanted with a new, larger nucleus as part of the same procedure, and returned to the water for another two years of growth.
The original Japanese cultured pearls, known as Akoya pearls, are produced by a species of small oysters no bigger than 6 to 7 mm in size, hence Japanese pearls larger than 10 mm in diameter are extremely rare and highly priced. In the past couple of decades, cultured pearls have been produced with larger oysters in the south Pacific and Indian Ocean. South Sea pearls are characterized by their large size and silvery color. Sizes up to 14 mm in diameter are not uncommon. Australia is one of the most important sources of South Sea pearls.
Recently (in the 1990s), the Japanese also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China, and Fiji. Freshwater pearls are characterized by the reflection of rainbow color in the luster. Cultured pearls are also being produced using abalone.
In Jewelry
The value of the pearls in jewelry is determined by a combination of the luster, color, size, lack of surface flaw and symmetry that are appropriate for the type of pearl under consideration. Among those attributes, luster is the most important differentiator of pearl quality according to jewelers. All factors being equal, however, the larger the pearl the more valuable it is. Large perfectly round pearls are rare and highly valued. Teardrop-shaped pearls are often used in pendants. Irregular shaped pearls are often used in necklaces.
Pearls come in eight basic shapes, round, semi-round, button, drop, pear, oval, baroque, and ringed. Perfectly round pearls are the rarest and most expensive, and are generally used in necklaces, or strings of pearls. Semi-rounds are also used in necklaces or in pieces where the shape of the pearl can be disguised to look like it is a perfectly round pearl. Button pearls are like a slightly flattened round pearl and can also make a necklace, but are more often used in single pendants or earring where the back half of the pearl is covered, making it look like a larger, round pearl.
Drop and pear shaped pearls are sometimes refered to as teardrop pearls and are most often seen in earrings, pendants, or as a center pearl in a necklace. Baroque pearls have a different appeal to them than more standard shapes because they are often highly irregular and make unique and interesting shapes. They are also commonly seen in necklaces. Ringed pearls are characterized by concentric ridges, or rings, around the body of the pearl.
There is also a unique way of naming pearl necklaces. While most other necklaces are simply refered to by their physical measurement, strings of pearls have their own set of names that characterize the pearls based on where they hang when worn around the neck. A collar will sit directly against the throat and not hang down the neck at all, they are often made up of multiple strands of pearls. Pearl chockers nestle just at the base of the neck. The size called a princess comes down to or just below the collarbone. A matinee of pearls falls just above the breasts. An opera will be long enough to reach the breastbone or sternum of the wearer, and longer still, a pearl rope is any length that falls down further than an opera.
Necklaces can also be classified as uniform, where all the pearls are the same size, graduated, where pearls change in size from large in the center to several millimeters smaller at the ends, and tin cup, where pearls are generally the same size, but separated by lengths of chain.
See also
External links
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