PearlsA pearl is a hard, generally spherical object produced within the soft tissue (specifically the mantle) of a living shelled mollusk. Just like the shell of a mollusk, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes of pearls (baroque pearls) occur. The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries, and because of this, the word pearl has become a metaphor for something very rare, fine, admirable, and valuable.Valuable pearls occur in the wild, but they are very rare. Cultured or farmed pearls from pearl oysters make up the majority of those that are currently sold. Pearls from the sea are valued more highly than freshwater pearls. Imitation or fake pearls are also widely sold in inexpensive jewelry, but the quality of their iridescence is usually very poor - and generally speaking, artificial pearls are easily distinguished from genuine pearls. Pearls have been harvested and cultivated primarily for use in jewelry, but in the past they were also stitched onto lavish clothing. Pearls have also been crushed and used in cosmetics, medicines, or in paint formulations.Pearls that are considered to be of gemstone quality are almost always nacreous and iridescent, like the interior of the shell that produces them. However, almost all species of shelled mollusks are capable of producing pearls (formerly referred to as "calcareous concretions" by some sources) of lesser shine or less spherical shape. Although these may also be legitimately referred to as "pearls" by gemological labs and also under U.S. Federal Trade Commission rules,[1] and are formed in the same way, most of them have no value, except as curios.Almost any shelled mollusk can, by natural processes, produce some kind of "pearl" when an irritating microscopic object becomes trapped within the mollusk's mantle folds, but the great majority of these "pearls" are not valued as gemstones. Nacreous pearls, the best-known and most commercially-significant pearls, are primarily produced by two groups of molluscan bivalves or clams. A nacreous pearl is made from layers of nacre, by the same living process as is used in the secretion of the mother of pearl which lines the shell.A "natural pearl" is one that forms without any human intervention at all, in the wild, and is very rare. Many hundreds of pearl oysters or pearl mussels have to be gathered and opened, and thus killed, in order to find even one wild pearl, and for many centuries that was the only way pearls were obtained. This was the main reason why pearls fetched such extraordinary prices in the past. A cultured pearl, on the other hand, is one that has been formed with human intervention on a pearl farm. One family of nacreous pearl bivalves, the pearl oysters, lives in the sea while the other, very different group of bivalves live in freshwater; these are the river mussels such as the freshwater pearl mussel. Saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae. Freshwater pearls grow within certain (but by no means all) species of freshwater mussels in the order Unionida, the families Unionidae and Margaritiferidae.The unique luster of pearls depends upon the reflection, refraction, and diffraction of light from the translucent layers. The thinner and more numerous the layers in the pearl, the finer the luster. The iridescence that pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. In addition, pearls (especially cultured freshwater pearls) can be dyed yellow, green, blue, brown, pink, purple, or black.Freshwater and saltwater pearlsShell of one species of freshwater pearl mussel, Margaritifera margaritifera.Freshwater and saltwater pearls may sometimes look quite similar, but they come from different sources.Natural freshwater pearls form in various species of freshwater mussels, family Unionidae, which live in lakes, rivers, ponds and other bodies of fresh water. These freshwater pearl mussels occur not only in hotter climates, but also in colder more temperate areas such as Scotland: see the freshwater pearl mussel. However, most freshwater cultured pearls sold today come from China.Saltwater pearls grow within pearl oysters, family Pteriidae, which live in oceans. Saltwater pearl oysters are usually cultivated in protected lagoons or volcanic atolls.

Although the traditional source of pearls has been saltwater mollusks, freshwater mussels, which live in ponds, lakes and rivers, can also produce pearls. China has harvested freshwater pearls in the form of mabe since the 13th century, and has now become the world's undisputed leader in freshwater pearl production. The first record mentioning pearls in China was from 2206 BC. The United States was also a major source of natural freshwater pearls, from the discovery of the New World, through the 19th century, until over-harvesting and increasing pollution significantly reduced the number of available pearl-forming mussels in the US.Generally speaking, freshwater pearls are not as round as saltwater pearls, and they do not have the same sharp luster and shine as akoya pearls. However, they appear in a wide variety of shapes and natural colors, and they tend to be less expensive than saltwater pearls, making them very popular with younger people and designers. Also, because freshwater pearls are solid nacre, they are also quite durable, resisting chipping, wear, and degeneration.With a total production of 1,500 tons in 2006, China holds a monopoly over the pearl industry today. Although the birth of the Chinese freshwater pearl industry is traced back to the area around Shanghai, freshwater pearls are now produced in all the surrounding provinces including: Zhejiang, Anhui, Jiangsu, Hubei, Hunan, and Jianxi. Local pearl trade is conducted mainly in the cities of Zhuji (Shanxiahu), Suzhou, Wuxi, Wenling, and Weitang. The largest marketplace for these freshwater pearls is the world's pearl trading hub, Hong Kong.What Makes Freshwater Pearls Different?

Freshwater pearls differ from other cultured pearls, in that the great majority of them are not bead-nucleated. Freshwater mollusks are nucleated by creating a small incision in the fleshy mantle tissue of a 6 to 12 month old mussel, then inserting a 3mm square piece of mantle tissue from a donor mussel. Upon insertion, the donor, (graft) tissue is twisted slightly, rounding out the edges. What happens after this point is really just speculation. Some believe that this tissue acts as a catalyst in producing a pearl sac thus making the 'nucleation' actual 'activation'. Others believe the tissue molds with the host to create a pearl sac, while still others maintain the tissue is the actual nucleus. Although it is said that a freshwater mollusk can withstand up to 25 insertions per valve, it is common industry practice to perform only 12-16 insertions in either valve, for a total production of 24-32 pearls. The mollusks are then returned to their freshwater environment where they are tended for 2-6 years. The resulting pearls are of solid nacre, but without a bead nucleus to guide the growth process the pearls are rarely perfectly round.The major increase in quality can be attributed to several factors. The primary jump in quality was accomplished when the industry shifted from the Cockscomb pearl mussel, (Cristaria plicata) to the Triangle shell, (Hyriopsis cumingii) in the middle 1990's. The Cockscomb was responsible for the low-quality rice-crispy pearls of the 1970's and 1980's. Another shift in quality can be attributed to the lower number of grafts inserted into either valve. This number has dropped by an average of 5 per side in the last decade. The turn of the century brought another wave of quality and exotic pearl colors in the form of mussel hybridization. The Japanese have a distinguished history of culturing freshwater pearls as well. Lake Biwa was once world renowned for producing high-quality freshwater pearls produced by the Hyriopsis schlegelii, (Biwa pearly mussel) mussel. However, in the mid 1970's pearl farming all but came to a halt due to pollution in this lake that was once synonymous with freshwater pearls. The Japanese tried once again to farm freshwater pearls in Lake Kasumigaura in the last decade, utilizing a bead-nucleated hybrid mussel (Hyriopsis Schlegelii/Hyriopsis cumingii). The resulting pearls have been quite large and unique. The Kasumiga pearl industry had a very short life span, however, with production ceasing in 2006. The industry is once again a pollution fatality of Japanese industry. The remaining Kasumiga pearls are exclusively sold by the Belpearl pearl company. Creation of a pearls

The difference between natural and cultured pearls focuses on whether the pearl was created spontaneously by nature without human intervention or with human aid. Pearls are formed inside the shell of certain mollusks: as a defense mechanism to a potentially threatening irritant such as a parasite inside its shell, or an attack from outside, injuring the mantle tissue. The mollusk creates a pearl sac to seal off the irritation.The mantle of the mollusk deposits layers of calcium carbonate (CaCO3) in the form of the mineral aragonite or a mixture of aragonite and calcite(Polymorphs with the same chemical formula, but different crystal structures) held together by an organic horn-like compound called conchiolin. The combination of aragonite and conchiolin is called nacre, which makes up mother-of-pearl. The commonly held belief that a grain of sand acts as the irritant is in fact rarely the case. Typical stimuli include organic material, parasites, or even damage that displaces mantle tissue to another part of the animal's body. These small particles or organisms enter the animal when the shell valves are open for feeding or respiration. In cultured pearls, the irritant is typically an introduced piece of the mantle epithelium, together or without a spherical bead (-> beaded or beadless cultured pearls). Natural pearlsNatural pearls are nearly 100% calcium carbonate and conchiolin. It is thought that natural pearls form under a set of accidental conditions when a microscopic intruder or parasite enters a bivalve mollusk, and settles inside the shell. The mollusk, being irritated by the intruder, forms a pearl sac of external mantle tissue cells and secretes the calcium carbonate and conchiolin to cover the irritant. This secretion process is repeated many times, thus producing a pearl. Natural pearls come in many shapes, with perfectly round ones being comparatively rare.Typically the build up of a natural pearl consists of a brown central zone formed by columnar calcium carbonate (usually calcite, sometimes columnar aragonite) and a yellowish to white outer zone consisting of nacre (tabular aragonite). In a pearl cross section such as in Fig. 6 these two different materials can be seen. The presence of columnar calcium carbonate rich in organic material indicates juvenile mantel tissue that formed during the early stage of pearl development. We know, e.g. from human medicine, that displaced cells with a well-defined task, continue to perform their function. The term "cyst" is applied to such situations. The displacement may occur with an injury. The fragile rim of the shell is exposed and is prone to damage and injury. Crabs, other predators and parasites such as worm larvae may produce traumatic attacks and cause injuries in which some external mantle tissue cells are disconnected from their layer. Embedded in the conjunctive tissue of the mantel, these cells may survive and form a small pocket in which they continue to secrete their natural product: calcium carbonate. The pocket is called a pearl sack, and grows with time by cell division; in this way the pearl grows also. The juvenile mantle tissue cells, according to their stage of growth, produce columnar calcium carbonate, which is secreted from the inner surface of the pearl sack. With ongoing time the external mantle cells of the pearl sack proceed to the formation of tabular aragonite. When the transition to nacre secretion occurs, the brown pebble becomes covered with a nacreous coating. As this process progresses, the shell itself grows, and the pearl sack seems to travel into the shell. However, it actually stays in its original relative position within the mantle tissue. After a couple of years, a pearl will have formed and the shell might be found by a lucky pearl fisher.Natural pearls are grown in wild oysters. The process begins when an irritant, such as a grain of sand or a piece of shell, gets inside an oyster's shell. To protect its delicate body from the irritant, the pearl secretes a substance called nacre to surround the irritant. The oyster never stops secreting nacre, so over the years the nacre layers build up into a genuine pearl.

While natural and cultured pearls are extremely similar, you can tell the difference between them with the right equipment. The key difference between natural and cultured pearls lies in the nacre layer. A natural pearl's nacre layer is much thicker than that of a cultured pearl, even when the two have a similar diameter.

Natural pearls are less transparent than cultured pearls. If you place a natural pearl against a dark backgroundlike a box lined in black clothand put it under a strong light, the natural pearl will look like a small, white, homogenous ball with no discernible inner rings. When you do the same to a cultured pearl, you will see a thin brown line between the nacre layer and the nucleus of the pearl.

Under an X-ray, natural and cultured pearls have a different internal structure. Cultured pearls will show concentric growth rings, while natural pearls will appear internally solid, with no growth rings. This is because natural pearls are 100% nacre, whereas cultured pearls have an inner nucleus composed of the bead that was deliberately injected to produce a pearl. That is why natural pearls are sold by weight (carat of pearls) while cultured pearls are sold by size (diameter of pearls).

Natural pearls are extremely rare. In nature, only about one in 10,000 oysters will produce a pearl. Of those, only a small percentage will achieve the size, shape, and color of a desirable gemstone. The odds of finding a perfect natural pearl are around one in a million. Because of their rarity, natural pearls are hardly ever found in most pearl jewelry stores. Most pearls for sale in the market today have been cultued.

Value of a natural pearlQuality natural pearls are very rare jewels. The actual value of a natural pearl is determined in the same way as it would be for other "precious" gems. The valuation factors include size, shape, quality of surface, orient and luster.Single natural pearls are often sold as a collector's item, or set as centerpieces in unique jewelry. Very few matched strands of natural pearls exist, and those that do often sell for hundreds of thousands of dollars. (In 1917, jeweler Pierre Cartier purchased the Fifth Avenue mansion that is now the New York Cartier store for US$100 cash and a double strand of matched natural pearls valued at the time at US$1 million.)Keshi pearls, although they often occur by chance, are not considered natural pearls. They are a byproduct of the culturing process, and hence do not happen without human intervention. These pearls are quite small: typically a few millimeters in size. Keshi pearls are produced by many different types of marine mollusks and freshwater mussels in China.[5] Today many "keshi" pearls are actually intentional, with post-harvest shells returned to the water to regenerate a pearl in the existing pearl sac.Origin of a natural pearlPreviously, natural pearls were found in many parts of the world. Present day natural pearling is confined mostly to seas off Bahrain. Australia also has one of the world's last remaining fleets of pearl diving ships. Australian pearl divers dive for south sea pearl oysters to be used in the cultured south sea pearl industry. The catch of pearl oysters is similar to the numbers of oysters taken during the natural pearl days. Hence significant numbers of natural pearls are still found in the Australian Indian Ocean waters from wild oysters. X-Ray examination is required to positively verify natural pearls found today.Cultured pearlsCultured pearls are the response of the shell on a tissue implant. A tiny piece of mantle tissue of a donor shell is transplanted into a recipient shell. This graft will form a pearl sac and the tissue will precipitate calcium carbonate into this pocket. There are a number of options to produce cultured pearls: use freshwater or seawater shells, transplant the graft into the mantle or into the gonad, add a spherical bead or do it non-beaded. The large majority of saltwater cultured pearls are grown with beads, the trade name of the cultured pearls are Akoya, white or golden South sea, black Tahiti. The majority of beadless cultured pearls are mantle-grown in freshwater shells, tradename Chinese cultured pearls.

Cultured pearls (beadless or beaded) and imitation pearls can be distinguished from natural pearls by X-ray examination. Nucleated cultured pearls are often 'pre-formed' as they tend to follow the shape of the implanted shell bead nucleus. Once the pre-formed beads are inserted into the oyster, it secretes a few layers of nacre around the outside surface of the implant before it is removed after six months or more.When a cultured pearl with bead is X-rayed, it reveals a different structure to that of a natural pearl. A beaded cultured pearl shows a solid center with no concentric growth rings, whereas a natural pearl shows a series of concentric growth rings. A beadless cultured pearl (whether of freshwater or saltwater origin) may show growth rings, but also a complex central cavity, witness of the first precipitation of the young pearl sac.Gemological identificationA well equipped gem testing laboratory (e.g. SSEF, Guebelin, GIA, AGTA, HIRCO-INDIA) is able to distinguish natural pearls from cultured pearls by using a gemological x-ray in order to examine the center of a pearl. With an x-ray it is possible to see the growth rings of the pearl, where the layers of calcium carbonate are separated by thin layers of conchiolin. The differentiation of natural pearls from non-beaded cultured pearls can be very difficult without the use of this x-ray technique.Natural and cultured pearls can be distinguished from imitation pearls using a microscope. Another method of testing for imitations is to rub the pearl against the surface of a front tooth. Imitation pearls are completely smooth, but natural and cultured pearls are composed of nacre platelets, which both feel slightly gritty.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 and their sensitivity to changing climatic and ocean conditions. Before the days of cultured pearls, black pearls were rare and highly valued for the simple reason that white pearl oysters rarely produced naturally black pearls, and black pearl oysters rarely produced any natural pearls at all.Since the development of pearl culture technology, the black pearl oyster found in Tahiti and many other Pacific Island areas has been extensively used for producing cultured pearls. The rarity of the black cultured pearl is now a "comparative" issue. The black cultured pearl is rare when compared to Chinese freshwater cultured pearls, and Japanese and Chinese akoya cultured pearls, and is more valuable than these pearls. However, it is more abundant than the South Sea pearl, which is more valuable than the black cultured pearl. This is simply because the black pearl oyster Pinctada margaritifera is far more abundant than the elusive, rare, and larger south sea pearl oyster Pinctada maxima, which cannot be found in lagoons, but which must be dived for in a rare number of deep ocean habitats or grown in hatcheries.Black cultured pearls from the black pearl oyster Pinctada margaritifera are not South Sea pearls, although they are often mistakenly described as black South Sea pearls. In the absence of an official definition for the pearl from the black oyster, these pearls are usually referred to as "black Tahitian pearls".The correct definition of a South Sea pearl as described by CIBJO and GIA is a pearl produced by the Pinctada maxima pearl oyster. South Sea pearls are the color of their host Pinctada maxima oyster and can be white, silver, pink, gold, cream, and any combination of these basic colors, including overtones of the various colors of the rainbow displayed in the pearl nacre of the oyster shell itself.Pearls from other speciesBiologically speaking, under the right set of circumstances, almost any shelled mollusk can produce some kind of pearl, however, most of these molluscan pearls have no luster or iridescence. The great majority of mollusk species produce pearls which are not attractive to look at, and are sometimes not even very durable, such that they usually have no value at all, except perhaps to a scientist, a collector, or as a curiosity. These objects used to be referred to as "calcareous concretions" by some gemologists, even though a malacologist would still consider them to be pearls. Valueless pearls of this type are sometimes found in edible mussels, edible oysters, escargot snails, and so on. The GIA and CIBJO now simply use the term 'pearl' (or, where appropriate, the more descriptive term 'non-nacreous pearl') when referring to such items[6][7] and, under Federal Trade Commission rules, various mollusc pearls may be referred to as 'pearls' without qualification. A few species produce pearls that can be of interest as gemstones. These species include the bailer shell Melo (genus), the giant clam Tridacna, various scallop species, Pen shells Pinna (genus), and abalones. Another example is the conch pearl (sometimes referred to simply as the 'pink pearl'), which is found very rarely growing between the mantle and the shell of the queen conch or pink conch, Strombus gigas, a large sea snail or marine gastropod from the Caribbean Sea. These pearls, which are often pink in color, are a by-product of the conch fishing industry, and the best of them display a shimmering optical effect related to chatoyance known as 'flame structure'.Somewhat similar gastropod pearls, this time more orange in hue, are (again very rarely) found in the horse conch Pleuroploca gigantea.The largest pearl known was found in the Philippines in 1934. It is a naturally-occurring, non-nacreous, calcareous concretion (pearl) from a giant clam. Because it did not grow in a pearl oyster it is not pearly; instead the surface is glossy like porcelain. Other pearls from giant clams are known to exist, but this is a particularly large one. The pearl weighs 14 lb (6.4kg) and was supposedly first discovered by an anonymous Filipino Muslim diver off the island of Palawan in 1934. According to the legend as it is currently told, a Palawan chieftain gave the pearl to Wilbur Dowell Cobb in 1936 as a gift for having saved the life of his son. The pearl had been named the "Pearl of Allah" by the Muslim tribal chief, because it resembled a turbaned head. Another even more elaborate legend says that this object is actually the Pearl of Lao-Tzu, a cultured pearl created with a carved amulet and then supposedly progressively grafted into several giant clams, before supposedly being lost due to a shipwreck in 1745.[8] This legend has been discredited, however because this pearl is indeed the product of a giant clam, Tridacna gigas, which cannot be grafted. The pearl is also a whole pearl, not a mabe pearl, and whole pearl culturing technology is only 100 years old.The history of pearl hunting and pearl farmingFor thousands of years, most seawater pearls were retrieved by divers working in the Indian Ocean, in areas like the Persian Gulf, the Red Sea, and in the Gulf of Mannar. Starting in the Han Dynasty (206 BC220 AD), the Chinese hunted extensively for seawater pearls in the South China Sea. In the 14th-century Arabian Sea, the traveller Ibn Battuta provided the earliest known description of pearl diving by means of attaching a cord to the diver's waist.

When Spanish conquistadors arrived in the Western Hemisphere, they discovered that around the islands of Cubagua and Margarita, some 200km north of the Venezuelan coast, was an extensive pearl bed. One discovered and named pearl, La Peregrina, was offered to the Spanish queen.[citation needed] According to Garcilasso de la Vega, who says that he saw La Peregrina at Seville in 1507, (Garcilasso, "Historie des Incas, Rois du Perou," Amsterdam, 1704, Vol. II, P. 352.) this was found at Panama in 1560 by a negro who was rewarded with his liberty, and his owner with the office of alcalde of Panama.Margarita pearls are extremely difficult to find today and are known for their unique yellowish color. The most famous Margarita necklace that any one can see today is the one that then Venezuelan President Romulo Betancourt gave to Jacqueline Kennedy when she and her husband, President John F. Kennedy paid an official visit to Venezuela.[citation needed]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 mussels and oysters produce pearls. In a haul of three tons, only three or four oysters will produce perfect pearl.The development of pearl farmingToday, the cultured pearls on the market can be divided into two categories. The first category covers the beaded cultured pearls, includingincluding Akoya, South Sea and Tahiti. These pearls are gonad grown, and there is usually one pearl grown at a time. This limits the number of pearls at a harvest period. The pearls are usually harvested after one year for akoya, 24 years for Tahitian and South Sea, and 27 years for freshwater. This perliculture process was first developed by the British biologist William Saville-Kent who passed the information along to Tatsuhei Mise and Tokichi Nishikawa from Japan. The second category includes the non-beaded freshwater cultured pearls, as the Biwa or Chinese pearls. As they grow in the mantle, where on each wing up to 25 grafts can be implanted, these pearls are much more frequent and do saturate the market completely. An impressive improvement of quality has taken place in the last ten years when the former rice grain-shaped pebbles are compared with the near round pearls of today.The nucleus bead in in a beaded cultured pearl is generally a polished sphere made from freshwater mussel shell. Along with a small piece of mantle tissue from another mollusk (donor shell) to serve as a catalyst for the pearl sac, it is surgically implanted into the gonad (reproductive organ) of a saltwater mollusk. In freshwater perliculture, only the piece of tissue is used in most cases, and is inserted into the fleshy mantle of the host mussel. South Sea and Tahitian pearl oysters, also known as Pinctada maxima and Pinctada margaritifera, which survive the subsequent surgery to remove the finished pearl, are often implanted with a new, larger beads as part of the same procedure and then returned to the water for another 23 years of growth.Despite the common misperception, Mikimoto did not discover the process of pearl culture. The accepted process of pearl culture was developed by the british Biologist William Saville-Kent in Australia and brought to Japan by Tokichi Nishikawa and Tatsuhei Mise. Nishikawa was granted the patent in 1916, and married the daughter of Mikimoto. Mikimoto was able to use Nishikawa's technology. After the patent was granted in 1916, the technology was immediately commercially applied to akoya pearl oysters in Japan in 1916. Mise's brother was the first to produce a commercial crop of pearls in the akoya oyster. Mitsubishi's Baron Iwasaki immediately applied the technology to the south sea pearl oyster in 1917 in the Philippines, and later in Buton, and Palau. Mitsubishi was the first to produce a cultured south sea pearl although it was not until 1928 that the first small commercial crop of pearls was successfully produced.The original Japanese cultured pearls, known as akoya pearls, are produced by a species of small pearl oyster, Pinctada fucata martensii, which is no bigger than 6 to 8cm in size, hence akoya pearls larger than 10mm in diameter are extremely rare and highly prized. Today, a hybrid mollusk is used in both Japan and China in the production of akoya pearls. It is a cross between the original Japanese species, and the Chinese species Pinctada chemnitziiRecent pearl productionChina has recently overtaken Japan in akoya pearl production. Japan has all but ceased its production of akoya pearls smaller than 8mm. Japan maintains its status as a pearl processing center, however, and imports the majority of Chinese akoya pearl production. These pearls are then processed (often simply matched and sorted), relabeled as product of Japan, and exported. In the past couple of decades, cultured pearls have been produced using larger oysters in the south Pacific and Indian Ocean. The largest pearl oyster is the Pinctada maxima, which is roughly the size of a dinner plate. South Sea pearls are characterized by their large size and warm luster. Sizes up to 14mm in diameter are not uncommon. South Sea pearls are primarily produced in Australia, Indonesia and the Philippines.Mitsubishi commenced pearl culture with the south sea pearl oyster in 1916, as soon as the technology patent was commercialized. By 1931 this project was showing signs of success, but was upset by the death of Tatsuhei Mise. Although the project was recommenced after Tatsuhei's death, the project was discontinued at the beginning of WWII before significant productions of pearls were achieved.After WWII, new south sea pearl projects were commenced in the early 1950s in Burma and Kuri Bay and Port Essington in Australia. Japanese companies were involved in all projects using technicians from the original Mitsubishi south sea pre-war projects.Freshwater pearl farmingIn 1914, pearl farmers began growing cultured 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 which was at one time 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 has caused the virtual extinction of the industry. Japanese pearl farmers recently cultured a hybrid pearl mussel a cross between Biwa Pearl Mussels and a closely related species from China, Hyriopsis cumingi, in Lake Kasumigaura. This industry has also nearly ceased production, due to pollution.Japanese pearl producers also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China. China has since become the world's largest producer of freshwater pearls, producing more than 1,500 metric tons per year (in addition to metric measurements, Japanese units of measurement such as the kan and momme are sometimes encountered in the pearl industry).Led by pearl pioneer John Latendresse and his wife Chessy, the United States began farming cultured freshwater pearls in the mid 1960's. National Geographic Magazine introduced the American cultured pearl as a commercial product in their August 1985 issue. The Tennessee pearl farm has emerged as a tourist destination in recent years, but commercial production of freshwater pearls has ceased. Momme WeightFor many cultured pearl dealers and wholesalers, the preferred weight measure used for loose pearls and pearl strands is momme. Momme is a weight measure used by the Japanese for centuries. Today, momme weight is still the standard unit of measure used by most pearl dealers to communicate with pearl producers and wholesalers. Momme is pronounced "moh-may." One momme = 1/1000 kan. Reluctant to give up tradition, in 1891, the Japanese government formalized the kan measure as being exactly 1 kan = 3.75 kilograms or 8.28 pounds. Hence, 1 momme = 3.75 grams or 3750 milligrams.In the United States, 19th 20th centuries, through trade with Japan in silk cloth the momme became a unit indicating the quality of silk cloth, = the weight in pounds of 100 yards of silk cloth 45 inches wide.One carat = 4 grains = 200 milligrams = 1/5 gram One grain = 1/4 carat = 50 milligrams = 1/20 gram One momme = 18.75 carat = 3750 milligrams = 3.75 grams One kan = 18,750 carat = 3750 grams = 3.75 kilosWhy is momme weight still used in the cultured pearl industry? Though millimeter size range is typically the first factor in determining a cultured pearl necklace's value, the momme weight of pearl necklace will allow the buyer to quickly determine if the necklace is properly proportioned. This is especially true when comparing the larger south sea and Tahitian pearl necklaces.Pearls in jewelryThe 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.Pearls come in eight basic shapes: round, semi-round, button, drop, pear, oval, baroque, and circled. Perfectly round pearls are the rarest and most valuable shape. 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 earrings where the back half of the pearl is covered, making it look like a larger, rounder pearl.Drop and pear shaped pearls are sometimes referred 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. Circled pearls are characterized by concentric ridges, or rings, around the body of the pearl.In general, cultured pearls are less valuable than natural pearls, and imitation pearls are less valuable than cultured pearls. One way that jewelers can determine whether a pearl is cultured or natural is to have a gem lab perform an x-ray of the pearl. If the x-ray reveals a nucleus, the pearl is likely a bead-nucleated saltwater pearl. If no nucleus is present, but irregular and small dark inner spots indicating a cavity are visible, combined with concentric rings of organic substance, the pearl is likely a cultured freshwater. Cultured freshwater pearls can often be confused for natural pearls which present as homogeneous pictures which continuously darken toward the surface of the pearl. Natural pearls will often show larger cavities where organic matter has dried out and decomposed.Some imitation pearls are simply made of mother-of-pearl, coral or conch shell, while others are made from glass and are coated with a solution containing fish scales called essence d'Orient. Although imitation pearls look the part, they do not have the same weight or smoothness as real pearls, and their luster will also dim greatly.There is a special vocabulary used to describe the length of pearl necklaces. While most other necklaces are simply referred to by their physical measurement, pearl necklaces are named by how low they hang when worn around the neck. A collar, measuring 10 to 13 inches or 25 to 33cm in length, sits directly against the throat and does not hang down the neck at all; collars are often made up of multiple strands of pearls. Pearl chokers, measuring 14 to 16 inches or 35 to 41cm in length, nestle just at the base of the neck. A strand called a princess length, measuring 17 to 19 inches or 43 to 48cm in length, comes down to or just below the collarbone. A matinee length, measuring 20 to 24 inches or 50 to 60cm in length, falls just above the breasts. An opera length, measuring 28 to 35 inches or 70 to 90cm in length, will be long enough to reach the breastbone or sternum of the wearer; and longer still, a pearl rope, measuring more than 45 inches or 115cm in length, is any length that falls down farther than an opera.Necklaces can also be classified as uniform, or graduated. In a uniform strand of pearls, all pearls are classified as the same size, but actually fall in a range. A uniform strand of akoya pearls, for example, will measure within 0.5mm. So a strand will never be 7mm, but will be 6.5-7mm. Freshwater pearls, Tahitian pearls, and South Sea pearls all measure to a full millimeter when considered uniform.A graduated strand of pearls most often has at least 3mm of differentiation from the ends to the center of the necklace. Popularized in the United States during the 1950s by the GIs bringing strands of cultured akoya pearls home from Japan, a 3.5 momme, 3mm to 7mm graduated strand was much more affordable than a uniform strand because most of the pearls were small.Colors of pearl jewelryEarrings and necklaces can also be classified on the grade of the color of the pearl. While white, and more recently black, saltwater pearls are by far the most popular, other color tints can be found on pearls from the oceans. Pink, blue, champagne, green, black and even purple saltwater pearls can be encountered, but to collect enough of these rare colors to form a complete string of the same size and same shade can take y PBS Pearl History Special.How do oysters make pearls ?Most jewelry is fashioned out of precious metals and jewels that are found buried in the Earth, but pearls are found inside a living creature, an oyster. Pearls are the result of a biological process . the oyster's way of protecting itself from foreign substances. Oysters are not the only type of mollusk that can produce pearls. Clams and mussels can also produce pearls, but that is a much rarer occurrence. Most pearls are produced by oysters in both freshwater and saltwater environments. To understand how pearls are formed in oysters, you must first understand an oyster's basic anatomy. Oysters are bivalves, which means that its shell is made of two parts, or valves. The shell's valves are held together by an elastic ligament. This ligament is positioned where the valves come together, and usually keeps the valves open so the oyster can eat. These are the parts of an oyster inside the shell: Mouth (palps) Stomach Heart Intestines Gills Anus Abductor muscle Mantle As the oyster grows in size, its shell must also grow. The mantle is an organ that produces the oyster's shell, using minerals from the oyster's food. The material created by the mantle is called nacre. Nacre lines the inside of the shell. The formation of a natural pearl begins when a foreign substance slips into the oyster between the mantle and the shell, which irritates the mantle. It's kind of like the oyster getting a splinter. The oyster's natural reaction is to cover up that irritant to protect itself. The mantle covers the irritant with layers of the same nacre substance that is used to create the shell. This eventually forms a pearl. So a pearl is a foreign substance covered with layers of nacre. Most pearls that we see in jewelry stores are nicely rounded objects, which are the most valuable ones. Not all pearls turn out so well. Some pearls form in an uneven shape -- these are called baroque pearls. Pearls, as you've probably noticed, come in a variety of various colors, including white, black, gray, red, blue and green. Most pearls can be found all over the world, but black pearls are indigenous to the South Pacific. Cultured pearls are created by the same process as natural pearls, but are given a slight nudge by pearl harvesters. To create a cultured pearl, the harvester opens the oyster shell and cuts a small slit in the mantle tissue. Small irritants are then inserted under the mantle. In freshwater cultured pearls, cutting the mantle is enough to induce the nacre secretion that produces a pearl -- an irritant doesn't have to be inserted. While cultured and natural pearls are considered to be of equal quality, cultured pearls are generally less expensive because they aren't as rare.