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Natural Pearls vs. Cultured Pearls
 Natural pearls, are pearls formed by chance. The shape, size, and quality of natural pearls varies widly. Cultured pearls have been given a helping hand by man and are consistent in shape, size and quality. Cultured pearls can also be mass produced. Naturally occuring pearls develop when an irritant, usually a parasite, accidentally finds its way into a pearl oyster or other mollusk. The mollusk reacts by coating the irritant with layer upon layer of a substance known as 'nacre'. Nacre is an organic secretion that gives the pearl its iridescent beauty. This unique relationship gives birth to the natural pearl.
Cultured pearls are created by inserting a foreign object into an saltwater oyster or freshwater mollusk. The same process of natural pearl creation then takes place. Cultured pearls can only be distinguished from natural pearls through the use of x-rays, which reveals the nucleus of the pearl. Today, nearly all pearls are cultured.
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The History of Pearl Culturing
The cultured pearl was developed to guarantee a steady supply of pearls and to satisfy the ever increasing demands of the consumer. Modern-day cultured pearls are the result of discoveries made in the late 19th and early 20th centuries, by Japanese researchers Tatsuhei Mise, Tokishi Nishikawa, and Kokichi Mikimoto. Early in Mikimoto’s career he focused on saltwater mabé pearl production. He eventually perfected his technique for producing round cultured saltwater pearls. This technique involved inserting tissue into the gonad of an akoya mollusk. He patented this technique in 1916.
 Mikimoto's technique revolutionized the pearl industry by allowing consistent production of a large number of pearls. High quality, round pearls could now be produced by the millions; making them available and affordable to everyone. Today, the cultured pearl industry has essentially replaced the natural pearl industry with production of cultured freshwater pearls and cultured saltwater pearls including South Sea, Tahitian, and of course Mikimoto’s original akoya pearls.
By the 1980's the Chinese had entered the free-market and the demand for Chinese pearls exploded. Today China is the predominant commercial producer of freshwater pearls on pearl farms.
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Pearl Farming
 Today cultured pearls are grown by the thousands on pearl farms. The first step in the process is to obtain the mollusks that will be nucleated. The original practice was to simply collect the mollusks from their natural habitat. Today many pearl farms have an extensive breeding program. After fertilization and the intial growth period baby mollusks are moved to a "nursery" bed and tended for 1 to 2 years until they are large enough to be nucleated.
 Thousands of mollusks are nucleated and then cultivated for 2-5 years, the time required for a pearl to develop. Saltwater pearls are nucelated using a "bead" made of mother-of-pearl. This bead is covered with a piece of donor oyster tissue and implanted in the oyster's reporductive organ called the gonad. The pearl will develop in the shape of the "bead" that was implanted. The result of this process is very uniform pearls.
Freshwater pearls are grafted with mantle tissue only. The implants are placed in the valves rather than in the gonad of the mussel. Each mussel can accept 12 to 16 grafts per valve and will produce 24 to 32 pearls per culturing cycle. After the pearls have been nucleated they are returned to the beds to grow for several additional years.
Once the pearls are fully developed, they are harvested. The shell and meat of the saltwater akoya and freshwater mussel are discarded after harvesting. South Sea and Tahitian oysters are carefully hand harvested. For each fully developed pearl that is removed a new nucleus is implaneted in the already formed pearl sac. The oysters are then returned to the bed to grow another pearl. These particular oysters can be recultivated several times during their life cycle. After the pearls are harvested they are washed and sorted. Some pearls are then bleached, heat-treated or dyed.
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Like other farming, pearl farming depends as much on luck as on skill. A pearl farm can be devastated by water pollution, storms, excessive heat or cold, disease and other natural and man-made factors. In recent years Chinese pearl farms have been impacted negatively by severe storms, pollution and over production. This will lead to a decrease in availabilty and an increase in price of freshwater pearls.
Sources:
Pearls: A Natural History by Landman, Mikkelsen, Bieler and Bronson
www.pearl-guide.com/pearl-farms.shtml
www.costellos.com.au/pearls/cultivation.html
www.pbs.org/wgbh/nova/pearl/time.html
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