VARIETIES
True pearls are divided primarily into two classes, "oriental," and "fresh-water." By true pearls those creations are meant which consist of concentric layers of nacre or mother-of-pearl, as distinguished from similar formations by mollusks out of material that is not pearly.
In the early days pearls brought from the Orient were therefore called "Oriental" pearls. For the same reason the fine mellow luster which characterized and made them superior to others came to be known as the "orient" of the pearl. These pearls were taken from oysters found on the coasts of Ceylon, Arabia, and the Red Sea. Later, when the same kind of oysters containing similar pearls were found in other seas, they were also classified with them, until the term "oriental" is now applied usually to all true pearls taken from salt water mollusks, to distinguish them from those found in the fresh water mussels and other products of ocean shell-fish which, though similar in construction and composition, are not nacreous. Occasionally, however, the term is still applied specifically to pearls from the Indian Seas, though their "orient" or luster is not always finer than that of like pearls found in many other localities.
Pearl oysters are varieties of the Avicula Margaritifera, of which the Meleagrina Margaritifera is the most prolific of mother-of-pearl and pearls combined, and, the Indian excepted, yields the finest pearls. All pearl oysters do not produce sufficient mother-of-pearl to make their shells valuable, nor do they all contain pearls. The name therefore applies to all oysters whose secretions are productive, in some degree, of mother-of-pearl and therefore under favorable conditions of pearls also.
"Fresh-water" or "sweet-water" pearls are, as the name signifies, those found in the mollusks of inland waters. This mollusk is a mussel. The name "mussel" in Anglo-Saxon signifies something which retires on being touched. It is known as "Unio" of which there are many pearl-bearing varieties.
In both the sea oyster and the fresh-water mussel, other nacreous formations occur of irregular shape called "baroque" pearls. The orientals approach more nearly to the globular and hemispherical form of true pearls, having frequently the lumpy rotundity of a snowball and sometimes sections which are smooth and round. The fresh-water baroques are usually very irregular, often fantastically so. Many resemble the incisor teeth of man or distorted grains of corn. Slender pieces similar to the wing of a bird and therefore called "wing" pearls, or "hinge" pearls because they are found near the hinge of the shell, are common. Some are shaped like a flat spike nail. Unlike oriental baroques, the surface of a large proportion of the fresh-waters is grooved or indented and some show a beautiful iridescence. Large button baroques of fine luster and iridescent, especially when they have a decided tinge of pink, have come to be known of late as "rose" pearls. Another variety of pink baroques having a fairly regular shape with a lustrous and finely irregular pimply surface are known as "strawberry" pearls. These terms are applied indiscriminately to the two varieties however.
Another nacreous formation found in the mother-of-pearl oyster shells is the "blister." It is produced by the raising of the nacreous deposits above the level of the shell to cover some intruder of considerable size. This results in a growth similar in shape to a blister on the flesh, hence the name. It is cut out of the shell and used in various ways as a set for jewelry, or to imitate the bodies of insects or small animals. Others with a slightly higher dome and rounded oval shape, regular in form, are called "turtlebacks."
