At this time pollution and excessive harvesting caused the virtual extinction of this animal. Nowadays, almost all pearls used for jewelry are cultured by planting a core or nucleus into pearl oysters. Later Japanese pearls larger than 10 mm in diameter were produced which were extremely rare and highly prized. 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. The characteristic property of the South Sea pearls is their large size and silvery color. One of the largest pearl-bearing oysters is the Pinctada maxima, which is roughly the size of a dinner plate. Freshwater pearls are characterized by the reflection of rainbow colors in the luster.
This process gained Freshwater pearl beads tremendous popularity so much so that the name ‘Biwa Pearls’ became synonymous with freshwater pearls in general. Sizes up to 14 mm in diameter are not uncommon. This lake, the largest and most ancient in Japan, lies near the city of Kyoto. This along with a small scrap of mantle tissue from another oyster to serve as an irritant, it is surgically implanted inside the oyster. This mariculture process was first developed by Kokichi Mikimoto in Japan, who was granted a patent for the process in 1896. Production thus increased rapidly reaching the time of peak in 1971, when Biwa pearl farmers produced six tons of cultured pearls. In the past couple of decades, cultured pearls have been produced with larger oysters in the south Pacific and Indian Ocean.
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. The nucleus is usually a polished bead made from mussel shell. Australia is one of the major producers of South Sea pearls.
In 1914 pearl farmers of Japan began culturing freshwater pearls using the pearl mussels native to Lake Biwa. However, not all natural oysters produce 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.
In the 1990s, Japanese pearl producers also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China, and in Fiji. 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. In fact, in a haul of three tonnes, only three or four oysters will produce perfect pearls. 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. Cultured pearls are also produced using abalone.In the beginning pearl hunting was the only means known for harvesting pearls.
Eventually the process of culturing pearls was discovered. Another type of South Sea pearl is the Tahitian pearls also called as Titian pearls.