Cultured pearls share the same properties of natural pearls and are formed in oysters in an almost identical fashion. The only difference lies in the fact that the irritant in the oyster is implanted by man, rather than by Nature. In both cases, however, it is left to Nature to create its miracle. In the past pearl cultivation depended entirely on wild oysters. While this has persisted partly to the present, scientists in Japan have isolated strains of oysters possessing superior pearl-producing qualities. The process is referred to as ‘nucleation’ and the ‘nucleus’ is a mother of pearl bead made from freshwater mussels.