There are many types of pearls available. The natural pearls are made without human interference. The cultured pearls are made when a foreign substance is intentionally inserted into a living oyster. This method was first used in 1893.
The baroque pearls have an irregular shape. A Biwa pearl is an irregular shaped pearl which forms in the freshwater of Lake Biwa, Japan. Blister pearls grow attached to the inside of the shell. The black pearl is gray to black in color. Freshwater pearls form in fresh water mollusks and resemble puffed rice. Mabe pearls are cultivated blister pearls. Seed pearls are small, tiny pearls used in Victorian jewelry and are sewn on clothing.
Pearls vary in color from white to those with a hint of color, often pink, to brown or black. Each coloration depends on the type of mollusk and the water where the mollusk lived. Because the nacre is organic, pearls are very sensitive to extreme heat, acids, dryness, and humidity.