††Pearls are small, round silvery-white stones sometimes found in oyster shells. They are valued as gemstones.
In 1921 the Japanese discovered a method of artificially 'persuading' oysters to make pearls.
A piece of grit is inserted into the oyster, which reacts by coating it with the substance that makes a pearl. Gradually the layers build up and the pearl increases in size.
This type of pearl is called a 'cultured' pearl, and is cheaper than those found naturally because it can be mass produced.
