Just about any pearl you’ll find today - in a store, at a jeweler, or virtually anywhere else- is a cultured pearl. Cultured pearls are an effort made by pearl farmers in order to maintain the delicate balance of nature, while still responding to the demand for pearls in the jewelry marketplace. Culturing pearls began at the very beginning of the 20th century, when several inventors discovered the techniques required in order to cultivate pearls. The most famous of these inventors is a man named Kokichi Mikimoto, known today around the world as the father of Akoya pearl.
To being the pearl cultivation process, the pearl technicians introduce a foreign object such as a piece of tissue or a mother-of-pearl bead nucleus into a tiny incision made in the gonad of the host mollusk; this process is known as "grafting", basically nucleating the oyster or mussel, stimulating it to pearl formation. The automatic reaction of the mollusk is to grow a pearl sac around the irritant and begin coating it with layer of nacre to smooth it over.
Pearl farmers can create cultured pearls in either saltwater or freshwater, and in different types of mollusks.