However, if a 1.00ct. round diamond has a shallow cut, sometimes
called a "spread cut", it will be will look larger than a well-cut
stone of the same weight because its diameter will be larger than
6.5mm. You might think that's great, but the trade off is that the
spread cut diamond will often have a lifeless, glassy look, called
Conversely, when a 1.00ct. round diamond is cut too deep, it appears
to be of smaller size than a well-cut stone, because the diameter
will be smaller than the expected 6.5mm. This means that you are
paying for extra weight in the pavilion and girdle areas, which
doesn't add to the beauty of the diamond. Furthermore, the stone
will often appear dark and dull in the center, resulting in what's
called a "nailhead".
The take-home lesson is that it is very important to consider
only a well-cut diamond, even, if necessary, at the expense of the
other 3C's (carat, color and clarity). Superior cut will give you
superior light performance producing a bright and lively stone.
It may not be the biggest looking diamond on the block, but it will
be the BEST looking diamond!
The same arguments concerning shallow and deep cut stones also
hold for the other fancy shaped diamonds, although the proportions
will be different. You can read about this subject in our article
on fancy shapes.
A final word about weight representation. In the U.S.,
the Federal Trade Commission requires that diamonds be weighed to
one-thousandth of one carat (0.001ct.), but that the final weight
can be rounded to the nearest half point (0.005ct.). This means
that a diamond weighing 0.995ct. can be represented to you as a
1.00ct. stone. However, international convention is more strict,
and a weight can only be rounded to the next higher point (0.01ct.)
if the actual weight reaches 9/10ths (0.009ct.) of a point. For
example, the 0.995ct. diamond must be represented as a 0.99ct. stone,
and to be represented as a 1.00ct. diamond the stone must weight
0.999ct. before it can be rounded up to 1.00ct.
The GIA follows the more strict international convention in listing
the weights in their grading reports. AGS gives the actual weight
directly to 1/1000ct. in their grading reports. Dutton's Diamonds
follows and supports the more strict international convention in
carat weight representation.
Effect of carat weight on price: Because diamonds are more
rare the larger they are, the carat weight is not directly proportional
to the total asking price. For example, the total price of a 2ct.,
D, IF, stone is not twice the total price of an identical 1ct. stone,
but is more than three times the price, and an identically graded
3ct. diamond is about 7.7-times as expensive as the 1ct. stone.
Also, a premium is added to diamond prices as they reach and exceed
each 1/4ct. increment in weight. (Hint: One way you might save a
little money is by buying stones with weights just below those increments,
if you can find them.)