Mabe pearls are a type of assembled cultured pearl. Rather than forming as a loose pearl, they form as a blister on the inside of a pearl mollusk shell. The blister dome is cut away from the shell, the hollow area is filled and then a plain mother of pearl backing is applied to the bottom. In some cases, two mabe pearls may be attached back to back, giving the appearance of a single pearl. There is always a visible seam with mabe pearls, and care must be taken not to weaken the bond.