Blister Pearl Formations
Most consumers are not aware that beautiful “and valuable” pieces of jewelry are made from pearl shapes not traditionally found in the marketplace. Other than the more commonly seen round (spherical), oval, button, and tear-drop (symmetrical) shapes you find in most jewelry stores, exquisite pieces can be, and are, made from irregularly (baroque) shaped pearls.
Baroque-shaped pearls are generally much more affordable than spherical and symmetrical-shaped pearls. It is much more difficult to find perfectly round-shaped spherical or proportionally-shaped symmetrical pearls.
Pearl farmers can reasonably determine the shape of the pearls produced by the oyster (mollusk) by the shape and placement of the irritant within the mollusk’s shell. Still, perfectly round spherical pearls are extremely rare, and therefore very costly as compared to symmetrical and baroque pearls.
Blister Pearls Attached to Shell
Blister pearls occur when an irritant gets trapped against the oyster shell beneath the mantle tissue. The mollusk then secretes layers of nacre that covers the irritant to form a hemispherical pearl with a flat back. Designers make jewelry pieces by cutting out the blister pearl while it is still attached to the shell, or by cutting the pearl from the shell and filling the back with resin and capping it with a flat piece of nacre (mother-of-pearl). When the latter is done the finish piece is called a mabe pearl or pearl doublet.