New 10mm Multicolored Shell Pearl Necklace 18in Brand New Multicolored Shell Pearl Pearl Size: 9-10 mm 18 inches Alloy Clasp Shell Pearls are made from the inner lining of oyster shells, also known as Mother of Pearl. The substance is ground to a fine powder, shaped, dyed and coated with natural pearl nacre and then a protective coating to give it lustre. The shell pearl is a pearl made in the laboratory with natural materials but it is an imitation pearl.