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Cultured pearls are pearls which are formed within a cultured pearl sac with human intervention in the interior of productive living molluscs in a variety of conditions depending upon the mollusc and the goals. [1] Having the same material as natural pearls, cultured pearls can be cultivated in seawater or freshwater bodies. Over 95% of the pearls available on the market are cultured pearls.
A pearl is formed when the mantle tissue is injured by a parasite, an attack of a fish, or another event that damages the external fragile rim of the shell of a mollusk shell bivalve or gastropod. In response, the mantle tissue of the mollusk secretes nacre into the pearl sac, a cyst that forms during the healing process. Chemically speaking, this is calcium carbonate and a fibrous protein called conchiolin. As the nacre builds up in layers of minute aragonite tablets, it fills the growing pearl sac and eventually forms a pearl.
Natural pearls are initiated in nature more or less by chance, but cultured pearls are human-initiated, formed by inserting a tissue graft from a donor mollusk, upon which a pearl sac forms, and the inner side precipitates calcium carbonate, in the form of nacre or "mother-of-pearl".
The most popular and effective method for creating cultured pearls utilizes the shells of freshwater river mussels harvested in the Midwestern U.S., from Canada to the Gulf of Mexico. Shells with the common names "Washboard", "Maple Leaf", "Ebony", "Pimpleback", and "Three Ridge" are popular for use in pearl culture due to their compatibility with the host animal and the nacre they are to be covered by. These high-quality and sought-after shells are first sliced into strips and then into cubes. The edges and corners are ground down until they are a roughly spherical and then milled to become perfectly round, and brought to a highly polished finish.
One of the first recorded histories of cultured pearls was found in the ancient China during the Song Dynasty. The cultivation method was the same as the Mabe-pearl (half pearl) that we know of today. Instead of using the shells or saibo as the core, they used a mold to create a buddhist figure made from lead. The mold was then inserted into the freshwater mussel shell, Hyriopsis cumingii .
In 1637, Mr. Song Yingxing compiled a Chinese encyclopedia called Tiangong Kaiwu (天工開物). Chapter 18 of this collection mentioned about the pearls and the formation theory. Along the line of history and with the help of the Silk Road, Tiangong Kaiwu arrived in Europe and was translated. Scientists who were fascinated by the mysteries of pearls began their quest to find out how pearls are formed.
From the 16th to the 18th century, the western world advanced in pearl research as new technologies, such as microscopes, developed. Scientists began more sophisticated research on pearl formation, developing new theories one after another. Disease Causation Theory (Guillaume Rondeletius, 1507 - 1566), Egg Causation Theory (Chauveton, 1578), Sand Grain Causation Theory (Sir R. Redding, 1674), Parasite Causation Theory (D. E. von Baer, 1830), and the Pearl Sac Theory(William Saville Kent, 1893) were all theories that tried to explain the pearls' formation. [2]
Mikimoto Kōkichi 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 the first small commercial crop of pearls was not successfully produced until 1928. [3]
The original Japanese cultured pearls, known as akoya pearls, are produced by a species of small pearl oyster, Pinctada fucata , which is no bigger than 6 to 8 cm in size, hence akoya pearls larger than 10 mm in diameter are extremely rare and highly priced. Today, a hybrid mollusk is used in both Japan and China in the production of akoya pearls. Furthermore, other Pinctada and Pteria species are also used for producing cultured pearls today. [4]
The development of cultured pearls took much of the chance, risk, and guesswork out of the pearl industry, allowing it to become stable and predictable, and fostering its rapid growth over the past 100 years. Today, more than 99% of all pearls sold worldwide are cultured pearls. Colored pearls, which occur due to local chemicals inside the shell, much in the way of rubies or sapphires, can be made by inserting colored minerals into the mussel shell, e.g., cobalt chloride to create a pinkish color.
Cultured pearls can often be distinguished from natural pearls through the use of X-rays, which reveals the inner nucleus of the pearl.
The cultured pearls on the market today can be divided into two categories. The first category covers the beaded cultured pearls, including Akoya, South Sea, Tahiti, and the large, modern freshwater pearl, the Edison pearl. These pearls are gonad-grown, and usually one pearl is grown at a time. This limits the number of pearls at a harvest period. The pearls are usually harvested after one year for akoya, 2–4 years for Tahitian and South Sea, and 2–7 years for Edison. This perliculture process was first developed by British biologist William Saville-Kent, who passed the information along to Tatsuhei Mise and Tokichi Nishikawa from Japan. [5]
The second category includes the non-beaded freshwater cultured pearls, like 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 saturate the market completely. An impressive improvement in quality has taken place in the last 10 years,[ when? ] when the formerly rice grain-shaped pebbles are compared with the near round pearls of today. In the last two years,[ when? ] large, near perfectly round, bead-nucleated pearls up to 15 mm in diameter with metallic luster have been produced.
The nucleus bead 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 bivalve. South Sea and Tahitian pearl oysters, as Pinctada maxima and Pinctada margaritifera , respectively, which survive the subsequent surgery to remove the finished pearl, are often implanted with a new, larger bead as part of the same procedure, and then returned to the water for another 2–3 years of growth. An experimental process using a radio-frequency identification nucleus allows the provenance of cultured pearls to be tracked. [6]
A pearl nucleus or a bead for cultured pearl is a sphere (usually) or other shape (occasionally) formed only by cutting and polishing a nacreous shell used to accommodate the nacre secreted from a graft of mantle tissue, that eventually forms the centre of a beaded cultured pearl. [7] While the material can be of anything that does not negatively affect the health of a pearl oyster, the modern age pearl cultivators normally use freshwater bivalves that either come from the US Mississippi River or China's freshwater bodies located in Hunan and Jiangxi provinces.
A pearl is a hard, glistening object produced within the soft tissue of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium carbonate in minute crystalline form, which has deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes, known as baroque pearls, can occur. The finest quality of natural pearls have been highly valued as gemstones and objects of beauty for many centuries. Because of this, pearl has become a metaphor for something rare, fine, admirable and valuable.
Kokichi Mikimoto was a Japanese entrepreneur who is credited with creating the first cultured pearl and subsequently starting the cultured pearl industry with the establishment of his luxury pearl company Mikimoto.
A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer usually created by an animal or organism that lives in the sea. Most seashells are made by mollusks, such as snails, clams, and oysters to protect their soft insides. Empty seashells are often found washed up on beaches by beachcombers. The shells are empty because the animal has died and the soft parts have decomposed or been eaten by another organism.
Bivalvia or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs that have laterally compressed soft bodies enclosed by a calcified exoskeleton consisting of a hinged pair of half-shells known as valves. As a group, bivalves have no head and lack some typical molluscan organs such as the radula and the odontophore. Their gills have evolved into ctenidia, specialised organs for feeding and breathing.
Nacre, also known as mother-of-pearl, is an organic–inorganic composite material produced by some molluscs as an inner shell layer. It is also the material of which pearls are composed. It is strong, resilient, and iridescent.
Pinctada is a genus of saltwater oysters, marine bivalve mollusks in the family Pteriidae. These pearl oysters have a strong inner shell layer composed of nacre, also known as "mother of pearl".
Baroque pearls are pearls with an irregular, non-spherical shape. Shapes can range from minor aberrations to distinctly ovoid, curved, pinched, or lumpy shapes. Most cultured freshwater pearls are baroque because freshwater pearls are mantle-tissue nucleated instead of bead nucleated. Cultured saltwater pearls can also be baroque, but tend to be more teardrop-shaped due to the use of a spherical nucleation bead.
Unionida is a monophyletic order of freshwater mussels, aquatic bivalve molluscs. The order includes most of the larger freshwater mussels, including the freshwater pearl mussels. The most common families are the Unionidae and the Margaritiferidae. All have in common a larval stage that is temporarily parasitic on fish, nacreous shells, high in organic matter, that may crack upon drying out, and siphons too short to permit the animal to live deeply buried in sediment.
Cultured freshwater pearls are pearls that are farmed and created using freshwater mussels. These pearls are produced in Japan and the United States on a limited scale, but are now almost exclusively produced in China. The U.S. Federal Trade Commission requires that farmed freshwater pearls be referred to as "freshwater cultured pearls" in commerce. Quality of cultured freshwater pearls is evaluated through a grading system of a series of A values, based on luster, shape, surface, colour and matching.
A bivalve shell is the enveloping exoskeleton or shell of a bivalve mollusc, composed of two hinged halves or valves. The two half-shells, called the "right valve" and "left valve", are joined by a ligament and usually articulate with one another using structures known as "teeth" which are situated along the hinge line. In many bivalve shells, the two valves are symmetrical along the hinge line — when truly symmetrical, such an animal is said to be equivalved; if the valves vary from each other in size or shape, inequivalved. If symmetrical front-to-back, the valves are said to be equilateral, and are otherwise considered inequilateral.
Pinctada albina is a species of pearl oyster of the genus Pinctada, known as the Shark Bay shell. Another common name is the Arafura shell, endemic to Arafura Sea in Indonesia. It is called the "Amami gai" in Japan.
Keshi pearls are small non-nucleated pearls typically formed as by-products of pearl cultivation. A Japanese word also meaning "poppy", it is used in Japanese for all pearls that grew without a nucleus. Originally, keshi pearls referred to those pearls formed when a bead nucleus was rejected. More recently, keshi has been used to refer to second harvest pearls and even to freshwater non-nucleated pearls. However the later usage referring to freshwater pearls is considered erroneous by many leading gem trade associations. Because they have no nucleus, keshi pearls are composed entirely of nacre.
The Tahitian pearl is an organic gem formed from the black lip oyster. These pearls derive their name from the fact that they are primarily cultivated around the islands of French Polynesia, around Tahiti.
Pinctada maxima is a species of pearl oyster, a marine bivalve mollusk in the family Pteriidae, the pearl oysters. There are two different color varieties: the Gold-lipped oyster and the Silver-lipped oyster. These bivalves are the largest pearl oysters in the world. They have a very strong inner shell layer composed of nacre, also known as "mother of pearl" and are important to the cultured pearl industry as they are cultivated to produce South Sea pearls.
Imitation pearls are man-made faux pearls. They are not to be confused with cultured pearls, which are real pearls created through human intervention.
Pteria sterna, or commonly known as the rainbow-lipped pearl oyster or the Pacific wing-oyster, is a species of marine bivalve mollusk in the family Pteriidae, the pearl oysters. This oyster can be found in shallow water along the tropical and subtropical Pacific coast of America, its range including Baja California, Mexico and northern Peru.
Pinctada fucata, the Akoya pearl oyster (阿古屋貝), is a species of marine bivalve mollusk in the family Pteriidae, the pearl oysters. Some authorities classify this oyster as Pinctada fucata martensii. It is native to shallow waters in the Indo-Pacific region and is used in the culture of pearls.
Pteria penguin, commonly known as the penguin's wing oyster, is a species of marine bivalve mollusk in the family Pteriidae, the pearl oysters. It is native to the western and central Indo-Pacific region and is used for the production of cultured pearls. The generic name comes from Greek πτερον (pteron) meaning wing.
Pinctada margaritifera, commonly known as the black-lip pearl oyster, is a species of pearl oyster, a saltwater mollusk, a marine bivalve mollusk in the family Pteriidae. This species is common in the Indo-Pacific within tropical coral reefs.
Humans have made multiple uses of molluscs, including as food, and they feature in art and in literature.
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