Sadly, our love of pearls and desire to follow fashion has greatly reduced the number of natural pearls available in the world. The constant demand for natural saltwater pearls over the last 150 years led to the overfishing of the natural pearl beds and many of them were lost for good. Natural freshwater pearls suffered the same fate. Angel-wing pearls from the Mississippi River and nearby lakes were very popular with Art Nouveau jewellers in the 1900s, but these days they have all but disappeared from the waters. Natural pearls have become very expensive.
As the supply of natural pearls dwindled, the need to develop affordable cultured pearls became essential. The Japanese were the first to develop a reliable process, in which the mantle (outer membrane) of a three-year-old saltwater oyster is cut open and between 1 and 20 round mother-of-pearl beads implanted. The bead, or nucleus, stresses the oyster, which, to isolate the irritation, deposits nacre over it, creating a pearl. In cultured pearls the nucleus is large so that the time required for a pearl to develop is reduced – it takes three years for just 1 mm of nacre to form.