Posted on January 10, 2019 by Mary Hood | 0 Comments
Contrary to popular lore, pearls aren’t necessarily formed when a grain of sand enters an oyster. That’s likely a myth. Rather, pearls form when a tiny organism (probably a parasite) enters a shell-producing mollusk (a group that includes oysters, mussels, clams, marine snails, and abalone).
As a defensive mechanism, the mollusk forms a protective crystalline substance around the irritant. This protective substance is called “nacre.” Nacre is composed of calcium carbonate and protein, and it is both lighter and stronger than concrete. (It’s also the same substance that forms the inside of the mollusk’s shell.) Nacre gives pearls their gem-like luster.
Natural pearls of real value occur very rarely, however. In fact, a pearl of value occurs in less than one of every 10,000 pearl oysters. Moreover, it can take at least three years for an oyster to coat an irritant with enough nacre to form a gem-quality pearl. Low-quality pearls are often the result of a pearl being “rushed out” of the oyster after less than a year. With these pearls, the coating of nacre is too thin to create adequate luster.
Cultured pearls help meet the high demand for real pearls. In the case of cultured pearls, a bead or piece of shell called mother of pearl is surgically inserted into the oyster. The inserted piece is also sometimes called the “nuclei.” The mollusk reacts to the nuclei the same way it would to a natural parasite by layering it with nacre, thereby forming a pearl.
Although saltwater pearls have historically been considered more valuable, thanks to their natural roundness and luster, freshwater pearls, which were once usually irregularly shaped, may now look more like their saltwater counterparts due to advances in pearl farming technology. See more about the different types of real pearls.
Finally, there are imitation pearls, which are usually made by dipping a glass bead in a solution made of fish scales. Because nacre has a distinct grit, it’s usually possible to tell the difference between a real and imitation pearl by running your teeth over them. An imitation pearl will feel smooth while a real pearl, natural or cultured, will feel gritty.