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The cut of
the diamond determines its shape. There are many
different shapes for diamonds. What gives diamonds its
brilliance is its facets. Each flat surface you
see on a diamond is called a facet. These allow
light to enter the diamond where it refracts into a
rainbow of colors reflecting against other facets until
the light comes out another facet. A diamond cut
ideally will reflect the light towards your eyes as
shown in the example.
As the
image shows, an ideal cut diamond is more effective at
reflecting the light back at the viewer. The
less-than-ideal cuts lose the light either through the
side of the bottom.
Uncut
diamonds are studied and measured in many ways to find
its ideal proportions to maximize its light refraction
properties. Each facet must be cut at the correct
angle relative to each other. The top and bottom
halves must have the proper depth relative to each
other. The table must be the correct size in
proportion to the diamond. And finally, the crown
and pavilion must be perfectly aligned.
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These measurements and percentages are
different for each diamond, and are all
taken into account in the evaluation of a
diamond's cut. In fact, each diamond shape
(heart, round, oval, emerald, etc.) has its
own set of guidelines for what makes a
Premium or Good cut. An 'ideal cut' is a
specific set of guidelines that delineate
the proportions that give a diamond the
highest amount of fire and brilliance.
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Although
the proportions of an ideal cut vary depending on the
source you talk to (from jeweler to jeweler, country to
country), there are certain ranges that are generally
accepted as capable of evoking the most desirable fire
and brilliance from a stone. These ranges must cause the
light entering the diamond to be reflected and dispersed
through the table (top), not through the sides or bottom
But most of all, an ideal cut diamond must be cut to
bring out the stone's brilliance and fire, not retain
the most weight from the rough cut stone.
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JewelryOction.com measures each diamond we sell by
hand on a digital calipers. Our digital
caliper has a ±0.02mm margin of error.
The
following table describes our cut grades for a
round brilliant diamond. The table
percentage is the table width relative to the
width of the entire stone. This
relationship is important in determining the
maximum fire and brilliance of the stone.
A table percentage that is too big or too small
can effect how well the diamond disperses the
light. The depth percentage shows the
relationship of the length of the stone from the
table to the culet expressed as a percentage.
This depth-to-width relationship is responsible
for the diamond proportion resulting in the
proper refraction of light and maximum fire and
brilliance.
|
GRADE |
TABLE PERCENTAGE |
DEPTH PERCENTAGE |
|
Ideal (Best) |
53% - 57% |
59% - 62% |
|
Premium |
58% - 63% |
58% or 63% |
|
Good |
64% - 65% |
57.5 or 64% |
It's
important to note that some independent grading
laboratories do not grade a diamond's cut, while
others do. The Gemological Institute of America
(GIA), for example, will only give an evaluation
of the quality of a diamond's cut for round
brilliant diamonds. For all other diamonds, only
the shape and measurements of the stone are part
of the report. It does, however, give the
proportions of the diamond (depth and table
percentages), girdle thickness, and culet size
(if any) as well as a general rating of the
stone's finish, including its polish and
symmetry.
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