In the beginning pearl hunting was the only means known for harvesting pearls. A little before the start of the 20th century divers manually pulled oysters from ocean floors and river bottoms and checked each one of them individually for pearls. However, not all natural oysters produce pearls. In fact, in a haul of three tonnes, only three or four oysters will produce perfect pearls.

Eventually the process of culturing pearls was discovered. Nowadays, almost all pearls used for jewelry are cultured by planting a core or nucleus into pearl oysters. Normally it takes three years after the planting for the pearls to be ready for harvesting but it may take up to six years also before the pearls are produced and ready. This mariculture process was first developed by Kokichi Mikimoto in Japan, who was granted a patent for the process in 1896. The nucleus is usually a polished bead made from mussel shell. This along with a small scrap of mantle tissue from another oyster to serve as an irritant, it is surgically implanted inside the oyster. Oysters which survive the subsequent surgery to remove the finished pearl are often implanted with a new, larger nucleus as part of the same procedure and then returned to the water for another three years of growth.

Originally the cultured pearls in Japan known as Akoya pearls were produced by a species of small oysters no bigger than 6 to 7 cm in size. Later Japanese pearls larger than 10 mm in diameter were produced which were extremely rare and highly prized. In the past couple of decades, cultured pearls have been produced with larger oysters in the south Pacific and Indian Ocean. One of the largest pearl-bearing oysters is the Pinctada maxima, which is roughly the size of a dinner plate. The characteristic property of the South Sea pearls is their large size and silvery color. Sizes up to 14 mm in diameter are not uncommon. Australia is one of the major producers of South Sea pearls. Another type of South Sea pearl is the Tahitian pearls also called as Titian pearls.

In 1914 pearl farmers of Japan began culturing freshwater pearls using the pearl mussels native to Lake Biwa. This lake, the largest and most ancient in Japan, lies near the city of Kyoto. This process gained tremendous popularity so much so that the name “Biwa Pearls” became synonymous with freshwater pearls in general. Production thus increased rapidly reaching the time of peak in 1971, when Biwa pearl farmers produced six tons of cultured pearls. At this time pollution and excessive harvesting caused the virtual extinction of this animal. Japanese pearl farmers now culture a hybrid pearl mussel—a cross between the last remaining Biwa Pearl Mussels and a closely related species from other Chinese or Japanese lakes.

In the 1990s, Japanese pearl producers also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China, and in Fiji. Freshwater pearls are characterized by the reflection of rainbow colors in the luster. Cultured pearls are also produced using abalone.

Source :  http://www.jewelry-thailand.com/