An organic gemstone, obtained from the pearl oyster, a natural growth produced by irritation inside the shell. Pearls are usually ivory-white in colour with a lustrous sheen, although they can also be pink or steel grey. They have been used in jewellery since ancient times, usually set in gold, often as a border decoration or in settings with precious stones. ‘Baroque’ pearls are large, misshapen pearls which were particularly popular with Arts and Crafts jewellers. In 1899 the Japanese firm of Mikimoto developed cultured pearls.