shell,—commonly
known by the name of mother-of-pearl ; others ascribe it to a disease
of the oyster. In some instances, on bisecting a pearl it is found to
be composed of a series of layers or skins round a speck of some darker
substance; in others the middle of the pearl is hollow and of a
globular or spherical form; and in others again the pearl
appears perfectly solid, and of the same texture, colour, and formation
throughout. The Chinese, from a very remote period, have been in the
habit of inserting small beads, images, etc., in the shells of oysters
and mussels, and these have certainly become coated with a pearly
substance, but they are generally of a blackish tint, with very little
lustre, and far inferior in appearance to the pearls formed in the
laboratory of nature.
The
wonderful polish and consequent lustre of a fine pearl,—which in a
great measure constitutes its value, and has never yet been even
passably imitated—would appear to be caused by the friction of the soft
body of the oyster for a considerable length of time ; and this polish
in most cases exists only on the outer skin, as on removing the
exterior surface the next layers are usually dull in colour and dead in
lustre,—resembling a fish's eye In some cases, however, a pearl of very
bad exterior contains a fine and " lively '' kernel.
Pearls
are found of almost every imaginable colour, and of the most fantastic
shapes ; in some instances of considerable size, but those of both fine
quality and large dimensions are very rare. Sometimes a shell will
