Cultured pearl
Pearl

Cultured pearl

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. 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.

Development of a pearl

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.

Pearl nuclei: the core of modern cultured pearls

White pearl necklace
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.[2] 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.

Nucleation

Cultured dark Tahiti pearls — one of the pearls is cut to expose the manmade nucleus bead
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, Tahitian, 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.[3]

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

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