FRACTURE-FILLING
OF EMERALD
I was able to learn a great
deal about gemstone quality
from the emeralds I purchased
in Bogota Colombia, during the
23 years between 1966 and 1989.
Whenever possible, I avoided
buying emeralds with surface-reaching
fractures. However, one day
a customer approached us claiming
that an emerald purchased two
or three years earlier had changed
color. Immediate investigation
revealed a heavily included
emerald that we had no recollection
of ever selling. What had happened?
The oil that had been impregnated
into the emerald, through minute
surface-reaching fractures,
had evaporated. Using oil as
the finishing touch for emeralds
was originally considered akin
to a woman's wearing makeup
, and was not a source of concern.
Through the use of vacuum and
pressure techniques, though,
filling fractures with oils
and polymers has become more
sophisticated, directly resulting
in problems such as this customer’s
claim.
Untreated Zambian emeralds
were polished in Hong Kong between
1972 and 1980. These emeralds
had a dry look and feel. Though
it was known that a light application
of oil would improve their luster,
the dealers did not do so in
deference to maintaining their
quality standards. With the
proper information, consumers
will be able to make their own
judgments regarding quality.
In other words, they will be
able to properly choose between
untreated material appropriate
for high-quality jewelry that
they mean to keep and pass on
for generations, and material
that is fracture-filled with
oils or polymers and suited
to accessory-type items.
It
is possible to detect the presence
or absence of oil- or polymer
impregnation by observing surface-reaching
fractures and inclusions through
a microscope. Oil impregnation
may also be detected by immersing
an emerald in alcohol for one
or more days. |
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Surface-Reaching
Fractures
The fine line on the emerald, seen toward the right in the photograph,
and much thinner than the hair on the left, is a surface-reaching
fracture. From here, oil or polymers are introduced into the stone
to make the fracture less visible inside the stone. There is no need
for fracture-filling treatment in fine-quality emeralds. |
Weight
: 0.21 ct
Size (mm): L 4.2 x W 3.1 x D 2.23
Untreated
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Weight
: 0.71 ct
Size (mm): L 5.5 x W 5.3 x D 3.92
Fracture-Filled
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Interference
Colors
Notice the yellow flash of interference color seen inside the emerald
shown in the photomicrograph above. This interference occurs when
very small fractures that contain air are filled with oil or polymers,
and is the same effect as the rainbow colors seen in a thin film
of oil on the surface of water. This is one nondestructive technique
used to detect the presence of fracture-filling treatment. |
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JUDGING QUALITY
Rough emeralds usually are immersed
in baby oil after they are mined to
allow inspection of their interior
condition. This oil penetrates into
the emeralds because they are so heavily
included. In order to finish them
as untreated emeralds, they are first
thoroughly cleaned to remove any absorbed
oils, then polished while avoiding
imperfections to make gemstones out
of just the attractive portions. Excluding
material that is purposely treated
with oil, emeralds containing baby
oil that was not completely removed
should still be thought of as untreated.
Untreated emeralds are different from
fracture-filled material, in that
there is no oil present that might
evaporate to reveal hidden fractures.
Therefore, it is possible to establish
the gem-quality range at tone levels
4, 5, and 6, and beauty grades S and
A. On the other hand, material in
the C and D beauty grades will not
be sold without treatment. Though
they may look the same, it is important
to understand that there is a large
difference in value between stones
that are polished from high-quality
portions of crystals, and those that
are cut with the intention of hiding
imperfections through oil- or polymer
impregnation.
Even if an emerald is accompanied
by a laboratory report stating that
it has not been treated, caution is
necessary, as it is easy to impregnate
an emerald with oils after the laboratory
inspection. |
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