Pearls form by a nucleus entering an oyster or mussel. A nucleus can be anything from a particle of shell to a minute snail. The mollusc secretes layers of a protective substance to coat the nucleus called nacre. (pronounced nay-ker). The size and shape of the pearl is mainly determined by the size and shape of the irritant.
Today we see most pearls on the market in two varieties, freshwater and cultured.
Freshwater
The nucleus is introduced mainly as a piece of mantle into a oyster or mussel placed in freshwater rivers and lakes.
Cultured
The nucleus is introduced mainly as a shell bead in an oyster. Salt water pearls are formed in salt water lakes, gulf’s and bays.
Other pearl types you may see on the market include:-
Akoya
Saltwater cultured. They range in size from 1mm to 10mm and are usually light pink , white or yellowish in colour.
Southsea
Saltwater large white or yellow pearls ranging from 9 to 19 mm in size.
Black (or peacock)
Formed in the black lip oyster.
Biwa
Fresh water
Mabe'
Half a nucleus bead is inserted in its host. They are often backed with mother of pearl.
Pearls are graded on their luster, size and shape
