Natural pearls have always been extremely rare. Only a tiny percentage of mollusks (less than one in a thousand) will produce a pearl during their lifetime and most of these pearls will be unsuitable for jewelry, due to poor size, color or other flaws.
These days, natural pearls are even rarer, due to overharvesting and pollution. Most of the natural pearls on the market are reworked from estate jewelry. The vast majority of pearls available today are so-called cultured pearls. Like natural pearls, they are produced by mollusks. But they require the intervention of humans to get the process started.
Pearls can be cultured in both saltwater and freshwater species. A shell bead or a piece of mantle tissue from another individual is inserted into the interior of the animal. This operation must be done very carefully so that the creature not only survives, but accepts the "nucleus". If successful, this process induces the animal to form a "pearl sac", the cells of which secrete a layer of brownish protein called conchiolin over the irritant. This is followed by the secretion of numerous mineral layers of nacre, which is composed of calcium carbonate in the form of thin overlapping plates.
The composition and structure of this nacre is more or less identical to that which forms under natural conditions. The thin layers create diffraction that is responsible for the pearly surface luster. If the layers are sufficiently thick and properly aligned, the result will be the most prized of all pearl characteristics; an iridescence called "orient".
The culturing process in freshwater pearls takes from 6 months to 3 years or more, depending on the conditions, the species, and the pearl to be produced. The various species of freshwater mussel are capable of producing a wider range of natural colors than most saltwater mollusks. These more colorful hues include white, cream, yellow, gold, silver, blue, brown and gray. Furthermore, these pearls grow faster and will tolerate multiple tissue nucleations, so that a harvest of 30-40 pearls from a single mollusk is possible over two years. The slower growing bead-nucleated, saltwater types will generally yield only one or two pearls per mollusk. This is why freshwater cultured pearls are so much less expensive.
Primary sources of freshwater cultured pearls are China, Japan and the United States.
- First Published: November-30-2009
- Last Updated: August-15-2017
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