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After
harvest pearls are always
processed in one way or another. Akoya and
freshwater pearls are
routinely bleached, and all pearls are cleaned and polished before
sale. But there are treatments that should be noted on
cultured pearls that change
the aesthetic qualities of the gem.
After cleaning a polishing a
low-quality
cultured pearl, and if the
pearl does still not have a good luster or color, the farmer is left
with few options. He can sell the pearl at a steep discount, dispose
of the pearl, peel the
nacre to be sold and reuse
the
nucleus, or impose a
treatment to the pearl that will change its appearance. If the pearl
is a good candidate for treatment, this is the most common and
economically sensible approach for the farmer. There are three main
treatments that low-quality pearls undergo:
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Dyeing - The use of silver nitrate to darken the
nacre of the pearl.
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Irradiation - The use of gamma rays to darken the
nucleus of the pearl in
akoya pearls and the nacre layers in freshwater.
-
Luster treatments - Typically a coating treatment
placed on the surface of the pearl to artificially enhance the
luster.
Silver nitrate has been used
for many decades to darken the appearance of pearls. The chemical
penetrates the layers of
nacre and has a chemical
reaction with light or hydrogen sulfide gas to create a rich black
color. If the farmer wishes to create colors other than black he may
also use organic or inorganic dyes to produce another color variation.
This is a very popular treatment done to freshwater pearls as the
lower values give farmers more opportunity to experiment.
Akoya pearls are also
routinely "pinked" to enhance a more desirable rose overtone.
Irradiation has differing
effects from freshwater to saltwater
cultured pearls. The gamma
rays do not affect the nacre layers of a saltwater cultured pearl, but
in fact darken the nucleus of the pearl. An irradiated
saltwater pearl appears to
be gray or blue. The nacre of freshwater irradiated pearls, on the
other hand, if affected by the gamma rays and can become very dark.
Some of these freshwater treated pearls will also have an intense
metallic sheen and iridescent orient over their surface.
Coating a pearl to enhance its
luster is not widely practiced and is greatly frowned upon. This
coating is equivalent to a coat of clear nail polish. Although the
luster may appear to be fine, the coating may eventually chip or peel,
leaving a low-luster pearl visible beneath the surface. This is a
treatment to watch for as dishonest pearl dealers have passed these
pearls on to unsuspecting consumers in the past.
Although nearly all pearls on
the market today have been treated in some way, it can be difficult to
detect pearls treated to change color. One method of detecting dyed or
irradiated pearls is to check the matching of the strand. A strand of
natural color pearls will
typically vary slightly from pearl to pearl. A perfectly consistent
strand may be evidence of treatment.
By peering down the drill hole
of a dyed pearl one may also be able to see concentrations of color.
This residue is left from the dying process. When looking down the
drill hole of an irradiated pearl one may be able to detect a darkened
nucleus. This is strong
evidence of gamma-ray treatment.
Luster treatments are much
harder to spot. The most basic method, however, is to compare an
untreated strand with the suspect strand under at least 50X
magnification. The untreated pearl will have a scaly
nacre surface. The coated
pearl will have a smooth, glass-like surface.
... read more on
Pearls in Myth
Information
obtained from www.Pearl-Guide.com
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