Pearl
A pearl is a hard, rounded object produced by certain animals, primarily mollusks such as oysters. Pearls can be used in jewelry and also crushed in cosmetics or paint. Pearl is valued as a gemstone and is cultivated or harvested for jewellery. The pearl is also the birthstone of June.
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, or as most know it, mother-of-pearl.
The unique lustre 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, purple, or black. Black pearls, frequently referred to as Black Tahitian Pearls are highly valued because of their rarity; the culturing process for them dictates a smaller volume output and can never be mass produced. This is due to bad health and/or non-survival of the process, rejection of the nucleus (the small object such as a tiny fish, grain of sand or crab that slips naturally inside an oyster's shell or inserted by a human), and their sensitivity to changing climatic and ocean conditions.
History
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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. Not all natural oysters produce pearls, however. In fact, in a haul of three tonnes, only three or four oysters will produce perfect pearls.
Now, however, almost all pearls used for jewelry are cultured by planting a core or nucleus into pearl oysters. The pearls are usually harvested three years after the planting, but it can take up to as long as six years before a pearl is produced. This mariculture process was first developed by Kokichi Mikimoto in 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 then returned to the water for another three 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 cm in size, hence Japanese pearls larger than 10 mm in diameter are extremely rare and highly prized. In the past couple of decades, cultured pearls have been produced with larger oysters in the south Pacific and Indian Ocean. One of the largest pearl-bearing oysters is the Pinctada maxima, which is roughly the size of a dinner plate. 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. Tahitian pearls (also referred to as Titian pearls) are also another South Sea pearl.
In 1914 pearl farmers began culturing freshwater pearls using the pearl mussels native to Lake Biwa. This lake, the largest and most ancient in Japan, lies near the city of Kyoto. The extensive and successful use of the Biwa Pearl Mussel is reflected in the name "Biwa pearls," a phrase nearly synonymous with freshwater pearls in general. Since the time of peak production in 1971, when Biwa pearl farmers produced six tons of cultured pearls, pollution and overharvesting have caused the virtual extinction of this animal. Japanese pearl farmers now culture a hybrid pearl mussel—a cross between the last remaining Biwa Pearl Mussels and a closely related species from China—in other Japanese lakes.
In the 1990s, Japanese pearl producers also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China, and in Fiji. Freshwater pearls are characterized by the reflection of rainbow colors in the luster. Cultured pearls are also produced using abalone.
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Religious references
According to Rebbenu Bachya, the word "Yahalom" in the verse Exodus 28:18 means "Pearl" and was the stone on the Ephod representing the tribe of Zebulun.
In a parable, Jesus compared the Kingdom of Heaven to a Pearl of Great Price.
The Vedic tradition describes the sacred Nine Pearls which were first documented in the Garuda Purana, one of the books of Hindu holy text Atharvaveda.
See also
- Baroque pearl
- Mother-of-pearl
- Broome
- Ammolite — another organic gemstone formed primarily of fossil aragonite mollusk shells.
- Oyster