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Evaluating
Gem Diamonds
The
value of a gem diamond depends on several factors: size,
clarity, cutting quality, and correct proportions.Large
diamonds are rarer than small ones, and therefore morevaluable.
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The
price of a diamond does not go up in simple steps along
with size, however. A three-carat gem will cost far
more, per carat, than three times that of a one-carat
stone of comparable quality. |
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In
the past few years the number of larger crystals being mined
in Africa has been slowly decreasing, and the typical gem
crystal found is becoming smaller and smaller. This creates
a much higher premium on larger stones. Fashion does have
some effect on prices. Dealers find that in some years gems
between 1/2 and one carat are in greatest demand and large
stones do not sell quickly. In other years the reverse may
be true.
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Gem Cutting |
Color
is the most important single factor that contributes
to the value of a gem diamond. Several grading
scales are currently in use; on the GIA scale,
for example, the highest-quality color grades
are D, E, and F, ail corresponding to a pure "white"
color, with no tinge of yellow.
Further
along in the scale, corresponding to moving through
the al¬phabet to N, O, and P, a diamond would
have an increasingly yellowish tint and its value
would drop steadily, all other factors being constant.
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If
he yellow became very strong and attractive the
diamond might, how¬ever, be considered a "fancy
color," and its value would be much higher
than that of a so-called "off-color"
stone.To the untrained eye, two gems may both
appear "white," whereas am might actually
be F and the other J on the CIA scale, and the
differences in price could be as much as 35 percent.
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Color
grading can only be done accurately by comparing a stone with
a "master set" of graded gems of the same general
size. The diamonds should be ex¬amined through the back,
on a white background, and with a standard illumination. Obviously
grading is not a simple matter, and should always be done
by someone trained in the techniques. The lighting is especially
critical, and the best illumination for diamond grading is
a filtered, cool-white, fluorescent lamp.
Clarity refers to the presence of inclusions, spots, or flaws
in a gem. Most gemstones contain inclusions of other minerals,
which were in¬ corporate at the time of crystal growth.
Inclusions decrease the value of a diamond. Their size and
number can be determined by means of a magnifying glass or
microscope.
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