Pearls produced by the molluscs in their own natural habitat are natural pearls .
Pearls produced by artificially inducing the pearl growth in molluscs are called cultured pearls. Although pearl cultivation has been practiced by the Chinese for centuries, it was only in the 1890s that the Japanese developed a method that is commercially effective. Beads made of Mother of Pearl are inserted into the shells of 3-year old oysters, which are then placed in cages in the waters of the sheltered bay. The harvesting time depends on the rate of Nacre deposit which differs in different waters. Simulated Pearls Simulated pearls are made by coating glass or plastic bead s with a liquid called Pearl Essence , extracted from herring scales.