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Cut is by far the most confusing of the 4 Cs
and possibly the most important. Since a well cut diamond will
have incredible brilliance and fire while a poorly cut diamond
will appear glass like and lifeless.
In an ideally-proportioned diamond, all of the
light entering the diamond from the top will bounce within the
diamond and be reflected back through the top, giving the stone
maximum brilliance and fire. If the stone
is too shallow or too deep, some light will escape through the
bottom part of the diamond, giving the appearance of shadows when
viewed from the top.
It's easy to see that the deep-cut diamond shown
above will have a higher carat weight, but is clearly the
less desirable stone! Many jewelers will not discuss
cut proportions unless the customer specifically asks;
a stone rich in carat weight but poorly proportioned can be deeply
"discounted," giving the buyer a false impression of
a great deal.
When looking at diamonds under a microscope,
compare the form of each facet with the ideal forms presented
here. For example, a round diamond has exactly 58 facets
-- 33 above the girdle, and 25 below.
When looking at actual stones, refer
to the diagram above and try to identify and rate each of the
facets. Extra, absent, or deformed facets decrease the value
of the stone.
The girdle of a diamond is the
middle, or fattest part, of the diamond, and is measured from
"extremely thin" to "extremely thick":
Thin girdles are prone to chipping. Extremely
thick girdles hide a lot of weight, so you end up paying for a
heavier diamond that doesn't look that big. The ideal is
an even, medium girdle; this applies to all shapes EXCEPT for
the tip of the pear shape, in which a thick girdle
is preferred to make it less prone to damage. When examining
the girdle, make sure that it is well-faceted and polished, since
some diamond cutters will omit this step to save time and to avoid
removing weight from the stone.
The culet is the bottom part of
the diamond, where the pavilion comes together in a point (refer
to the diagram shown above, under "facets"). Culets
are rated as "none", "small", "medium",
and "large." The ideal is "none," but
if an otherwise perfect stone has a medium or large culet, it
may still be a worthwhile purchase.
Check the following aspects of
the stone to make sure it is completely symmetrical:
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Make sure the culet is precisely
in the middle of the stone when viewing it from the bottom
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Verify that the pavilion and
crown have the same angle all the way around the stone, and
are not bowed out or concave
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If you're purchasing a heart
shape or any other fancy shape, be sure there are
no deformities. For example, some heart-shaped diamonds
will have unsightly asymmetrical lobes. Some princess
shape or radiants are not quite
square.
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Inspect the table
to make sure it is flat and symmetrical
There's no hard and fast rule to
judge the finish of a stone. However, understand that the
more a diamond cutter polishes a stone, the more carat weight
it loses (and therefore its value), so the cutter's goal will
be to polish just enough to satisfy the potential customer.
Polishing will also remove any surface flaws relating to clarity,
so that potentially an IF diamond could be turned into an FL simply
by polishing it.
Cost
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