Beautiful Defense Mechanism

Natural pearls are the result of an accident--some foreign matter ends up in the tissue of a mollusk and the mollusk defends itself, much like our immune system attacks bacteria and viruses. In the mollusk's case, it attacks the object by coating it with a substance called "nacre," transferred molecule by molecule, from the mantle on the inside of its shell. Unless the object is expelled by the mollusk, the layers of nacre keep building. As the calcium carbonate-based nacre ("mother-of-pearl") builds on the object, its layers develop a deep, shining quality called "pearlescence." Natural pearls are seldom round, and their shape and color are dependent on the type of mollusk, the water in which it lives and its diet. Pearls were prized by ancient Chinese and Indian royalty, and the later Greek and Roman civilizations also valued them highly. One of the treasures hunted by New World explorers was the freshwater pearl, abundant in the lakes and streams of the great, unexplored wilderness. By the 19th century, the supply of freshwater pearls had begun to dry up and the Japanese had invented a technology to artificially grow pearls, known as culturing.

Freshwater Culture

The Japanese freshwater culturing process used lake mussels to grow pearls. Not all mollusks have mother-of-pearl mantles, and freshwater mussels became the mollusk of choice for the pearl farmers. A chip of nacre was taken from a donor mollusk and twisted into the tissue of a mollusk. Several dozen chips could be implanted in a parent, and generally more than a dozen would remain in the mussel long enough to grow into a marketable pearl. The mussel would be allowed to go about its business for 2 to 6 years as the pearls grew. At the end of that period, the pearls would be removed and the mussels, presumably, harvested for other uses. Japanese dominance in the freshwater cultured pearl business lasted until the second half of the 20th century when pollution began to foul the traditional lakes used for farming. Today, the Chinese produce the majority of the world's freshwater cultured pearls and Hong Kong is considered the pearl-trading capital of the world.

Changes in Culture

Freshwater cultured pearls have traditionally been tougher than natural pearls because nacre was used as the "seed" rather than stones, shells or insects, as happens in nature. They were also tougher than saltwater cultured pearls that used beads as seeds. Recently, though, freshwater pearl farmers have also begun to use beads to cut down on growth time and provide a perfectly round base shape for the finished pearl. Freshwater pearls are considered less luminous than saltwater pearls but are more often found in colors and shapes not found in their saltwater counterparts.