Around the commencement of the 20th century, researchers found that if a sphere of material was placed in an oyster, the oyster would coat the sphere with nacre, creating an almost perfectly round pearl. The longer the pearl remained in the oyster, the larger and more valuable it became. Almost all cultured pearls (as they are called) grown on pearl farms a growing industry in todays world. Different types of oysters or mollusks raised in different environments create cultured pearls in different sizes, colors and shapes. Man cultivates pearls by placing shell beads inside an oyster shell. The oyster is returned to the water for a length of time where it covers the bead with layers of nacre. Most cultured and quality pearls are produced in Japan. In the warm waters of the South Pacific, large oysters produce South Sea cultured pearls and Tahitian black cultured pearls. In China, freshwater pearls are cultured in freshwater mussels.

Cultured pearls and natural pearls can be easily distinguished from imitation pearls by performing a very simple test. By rubbing the pearl against the edge of a tooth one can see that a cultured and natural pearl will feel slightly rough, like fine sandpaper, because of the texture of natural nacre. An imitation pearl remains smooth because the surface is molded or painted and is not affected by exterior materials.

Pearls are generally cultivated in areas that have the right water temperature, are clean and nutritious. The ultimate quality of the cultured pearl depends on a number of factors such as the acreage of pollution free water available and the area where the farms are located. Pearl farms are usually located in areas with active tides and less water pollution. The big tides feed the oyster a rich mixture of organic food thus affecting the pearl quality.