Natural pearls and cultured pearls are produced through the same process. When a grain of sand naturally happens to infiltrate the oyster’s shell or in the case of “cultured” pearls a bead is meticulously placed in the oyster’s shell, both intrusions act as an irritant. The oyster responds by secreting a “liquid” pearl substance called “nacre.” Over time, usually years, layers of “nacre” encase the foreign object and a beautiful new entity is formed.