|
Cultured Pearls
The cultivation of pearls, which now accounts
for the a majority of pearls issued on the market each year,
involvas mentioned, introducing mother-of-pearl beads into
tissues of certain types of mollusks, which deposit c centric
layers of nacre around the foreign body. Th
spheres are quite large in relation to the final volume of
pearl. In fact, depending on the size of the mollusks, bea
from 1 to 3-4 millimeters in diameter are used (nucle 6-7
and even 8 millimeters are only used for Austra pearls).
Appearance Cultured pearls are generally
more sph• cal in shape than natural ones. Less regular,
baroque pear-shaped pearls are also found, or specimens sligr
flattened at one or both poles, which are inevitably of m
limited use. The most common types of minor irregularv are
either a small, almost conical protuberance or srr barely
noticeable cavities with a white base, resemb, lunar craters,
which are also found, though much Ir often, in natural pearls.
Protuberances are partially moved with a file, and the site
is used for the holc pierced pearls. When magnified twenty
or more times. :: tured pearls also display a close pattern
of minute, sinu,lines. As with natural pearls, the normal
color is gray-wr to yellowish gray-white, but cultured pearls
sometimes c play a rather unattractive greenish tinge in strong
lic Their luster and iridescence are not noticeably differ,
from those of natural pearls.
One does not normally see r faint gray, dark-centered
coloration of natural pearls, t cultured pearls may be a definite
gray color, even in w layers near the surface; this coloration
is always artifr and due to treatment. Cultured pearls often
have hic translucent outer layers because of an excess of
water conchiolin, which makes them more liable to deterior
Australian cultured pearls are a special case. Being •,
duced by large mollusks, they are often 10-12 millimein diameter,
and even over 15 millimeters, with striking ter, great compactness
and a very white, almost sil. color, probably due to lack
of bleaching, but no iriccence. They may be perfectly spherical,
but somen have a series of small furrows arranged like the
paralle a globe, or are slightly flattened at the poles, or
tend v biconical shape.
Distinctive features In pierced cultured
pearls, the juction between the external layers of nacre and
the unifc nucleus at the center may be quite clearly visible
thro~. the drill hole, not always easy to see with a lens,
but c tainly visible with a good binocular microscope of 15>
20x magnification. It is most easily recognizable when ' hole
that has been drilled is at the site of a small protut ance,
which has been filed down and which generally ha small cavity
bounded on the inside by the convex surf., of the spherical
nucleus.
1 - 2
|
