e been found
with mummies or in ancient ruins. The organic matter has yielded to
bacterial attack and decayed, leaving only the powdery mineral matter
behind. As heat and moisture are the conditions most conducive to the
growth of bacteria, and hence to decay, it would follow that fine pearls
should be kept in a dry cool place when not in use.

LESSON XXVIII

CULTURED PEARLS AND IMITATIONS OF PEARLS

CULTURED PEARLS. Like all very valuable gems, pearls have stimulated the
ingenuity of man to attempt to make imitations that would pass for
genuine. Perhaps the most ingenious, as well as the most natural looking
product, is the "_cultured pearl_." This is really natural pearl on much
of its exterior, but artificial within and at the back. In order to
bring about this result the Japanese, who originated the present
commercial product, but who probably borrowed the original idea from the
Chinese, call to their assistance the pearl oyster itself. The oysters
are gently opened, small hemispherical discs of mother-of-pearl are
introduced between shell and mantle and the oyster replanted. The
foreign material is coated by the oyster with true pearly layers as
usual, and after several years a sufficiently thick accumulation of
pearly layers is thus deposited on the nucleus so that the oyster may be
gathered and opened and the cultured pearl removed by sawing it out from
the shell to which it has become attached. To the base is then neatly
cemented a piece of mother-of-pearl to complete a nearly spherical
shape, and the portions of the surface that have not been covered with
true pearl are then polished. The product, when set in a proper pearl
mounting, is quite convincing and really beautiful.

As the time during which the oyster is allowed to work upon the cultured
pearl is doubtless far less than is required for the growth of a large
natural pearl, the number of layers of true pearly material is
considerably smaller than the number of layers that take part in the
multiple reflections explained in the previous lesson, and hence the
"orient" of the cultured pearl is never equal to that of a fine true
pearl. It is frequently very good however, and for uses that do not
demand exposure of the whole surface of the pearl, the cultured pearl
supplies a substitute for genuine pearls of moderate quality and price.
The back parts of the cultured pearl, being only polished
mother-of-pearl, have the appearance of the ordinary pe