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Why does the diamond
look great while the quartz looks terrible? The answer lies
in the fact that the two materials have very different refractive
indices. A good gemcutter would
recognize the need to adjust the pavilion angles to compensate
for this. Unfortunately, windowing is so common among commercially-cut
gemstones that many consumers have come to accept it as normal.
Proper design selection will prevent this, regardless of the
gemstone.
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Another physical
property that enters into design consideration is the
gemstone's depth of color. Stones that are darker in
color are sometimes cut in a more shallow, "bright"
design, while those that are lighter may be cut in a
deeper design. Both strategies seek to bring out the
best possible color in the stone. In addition, stones
that have very subtle color may be deliberately cut
in designs that produce a minimum of "visual excitement"
or scintillation, as this can sometimes wash out the
very color that you're working to preserve.
The photos to the left illustrate
the different approaches discussed above. In the top
photo, a fiery mandarin spessartite garnet (refractive
index: 1.79-1.81 with med.-high dispersion) is cut in
a brilliant oval design to maximize the sparkle and
fire. Due to its rich coloration, there is no risk of
washing out the color. In the bottom photo, an emerald
(refractive index: 1.59 with low-med. dispersion) is
cut in a "low-sparkle," classic emerald cut
to emphasize the color that makes emeralds so highly-prized.
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