|A Natural pearl is formed when an irritant accidentally gets into the soft tissue of an oyster or mussel. As a defense mechanism, the animal produces secretions to coat the irritant. Many layers of coating are deposited on the irritant making the irritant smooth. A natural pearl is thus born.
A cultured pearl is formed in the same process as a natural pearl. The only difference is that it begins with inserting a shell bead nucleus inside the oyster and irritating the oyster to produce layers of nacre.
Why natural pearls are so rare? It may take over 100,000 oysters to get enough pearls to make a pearl necklace. Matching for natural pearl strands is extremely difficult since they are never round or uniform in size and color. A well matched natural pearl strand can have extremely high price.
The technique for Cultured pearls was invented by Kokichi Mikimoto in 1900s. Before then, natural pearls were extraordinarily valuable and expensive. In the history of pearls, natural pearls were favored and treasured by nobles and they would trade a mansion for a strand of natural saltwater pearls.
As Mikimoto expanded his cultured pearl production and cultured pearls gained acceptance in 1930s, the value of natural pearls decreased dramatically. A normal buyer could hardly notice the difference between a half million dollar strand of natural pearls and a strand a Japanese cultured pearls.
Nowadays, nearly all pearls sold in the market are cultured pearls. Natural pearls are only treated as antiques.