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answer to this problem is to cement the opal layer to
a backing material to give it thickness and strength.
The most common backing materials are common opal (called
potch), onyx, and a ceramic material.
The
resulting two-layer sandwich is called a doublet; the
cement used between the layers is usually blackened
to accen¬tuate the colors in the thin, precious
opal layer. From the top a doublet looks like a fine
black opal, even though the precious opal used is whit,
opal.
But the opal layer on a doublet is still exposed to
wear, and can suffer damage if not cared for.
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In
recent years this problem has also been solved by the
creation of the triplet. This is a doublet, on top of
which is cemented a cabochon of colorless quartz.
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The
quartz adds additional thickness to the stone prevents damage
in setting, and protects the opal layer from wear. In addition,
the quartz cabochon has the effect of a magnifying glass.
enlarging the color play and giving more of the appearance
of fine black opal.
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OPAL |
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OPAL
By far the finest and most treasured opals come
from Australia. Some Australian opals are so spectacular
that they were given individual names, such as
the Empress, the Red Admiral, the Pandora, Light
of the W the Harlequin Prince. White opal may
sell for a few dollars hundred dollars per carat.
A fine black opal, however, can more than $1,000
per carat.
Gem
quality opal comes from Honduras, though Honduran
opal is not commercially significant today. Czechoslovakia
was the source of Roman opal, especially the town
of Czerwenitza, which was formerly in and whose
deposits were extensively mined before 1800. Mexico
produces fine water opal and fire opal, sometimes
with a striking color play. Fine precious opal
comes from the Virgin Valley in where the opal
generally replaces wood and animal bones, in the
manner of petrified wood. In recent years a quantity
of white ~ opal from Brazil has been marketed.
This material, some of it rivaling the best Australian
white opal, is more heat resistant and less wan
Australian white opal.
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Terms
sometimes applied to gem opal are harlequin (a
mosaic of patches of fire); flame opal (regular
color bands or streaks); gold opal (the whole
surface of which glows with a golden sheen); girasol
(a wave of blue light on a transparent background);
opal-onyx, a material built up of alternating
layers of common opal and precious opal.
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Frequently,
as in the case of opal-onyx, opal is mined that is essentially
devoid of fire, but contains a very thin layer of precious
opal. This ¬can be exposed by careful cutting, but if
the layer is in a thin seam of white opal there may not be
enough support Left to yield a stone that can be used in jewelry.
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