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Diamond Cut
Grading
A rough
diamond looks like any other rock until it is "cut" into many facets at optimum
angles to produce maximum brilliance (sparkle) and fire (reflected colors). The
quality of the cut is known as the "make".
In 1919
Marcel Tolkowsky developed the formula for the round brilliant cut which
has become the standard or "ideal" cut for diamonds. Since then there have been
various modifications and disagreement over what constitutes the true "ideal"
cut. However, the Gemological Institute of America (GIA) has developed the
following guidelines for grading the make of round brilliant cut diamonds only.
The
Table Size % is the ratio of the table diameter to the girdle
diameter. The Depth % is the ratio of the distance between
the table and the culet to the girdle diameter. These are the
two most important factors in determining the grade of a diamond's
cut.
Round Brilliant Cut Diamonds only.
| KEY FACTORS |
Class 1
Premium Cut |
Class 2 Well Cut |
Class 3 Cut Average |
Class 4 Cut Below Avrg |
| Table Size |
53-60%
of diameter |
61-64% |
65-70% |
over
70% |
| Depth
|
58-63%
of diameter |
57-64% |
56-66% |
under
56% over 66% |
| Crown
Angles |
34-35
degrees |
32-34
degrees. |
30-32
degrees |
less
than 30 degrees |
| Girdle
Thickness |
medium
- slightly thick |
thin-thick |
thin or
very thick |
knife
edge or very thick+ |
| Polish
& Symmetry |
very
good - excellent |
good |
fair |
poor |
More
detailed charts were developed by David Atlas for fancy cut diamonds and are
used by Accredited Gem Appraisers, D. Atlas & Company, Inc. and the National
Association of Jewelry Appraisers. Simplified versions for these charts are
shown below. (Revised: 3/02)
Princess Cut Diamonds
| KEY FACTORS |
Class 1 Cut Premium |
Class 2 Cut Fine Trade |
Class 3 Cut Average |
Class 4 Cut Below Avrg |
| Table Size |
60%-71%
of diameter |
58%-77% |
53%-85%
|
Below
53%
Above 85% |
| Depth |
64%-75%
of diameter |
58%-80% |
56%-84% |
Below
56% Above 84% |
| Crown
Height % |
8.5%-11% |
6.0%-13% |
4.0%-17.5% |
Below
4.0% Above 17.5% |
| Girdle Thickness |
thin-med or med.-thick |
thin-thick |
very
thin - very thick |
extra
thin - extra thick |
| Polish
& Symmetry |
good -
excellent |
fair
-good |
fair-good |
poor to
fair |
Pear, Marquise, Heart,
and Oval Cut Diamonds
| KEY FACTORS |
Class 1.
Premium Cut |
Class 2. Fine Trade Cut |
Class 3. Average Cut |
Class 4. Below Average |
| Table Size |
54%-61.5% of diameter |
52%-64% |
50%-70%
|
Below
50% Above 70% |
| Depth
|
59%-63%
of diameter |
58%-65.4% |
46%-71% |
Below
46% Above 71% |
| Crown
Height % |
12.5%-15% |
11.1%-16.5% |
8.7%-18.4% |
Below
8.7% Above 18.4% |
| Girdle
Thickness |
thin-med. or med.-thick |
thin-thick |
very
thin to very thick |
extra
thin to extra thick |
| Polish
& Symmetry |
good to
excellent |
good to
excellent |
good to
fair |
fair to
poor |
| Length: Width Ratios |
Class 1 & 2
Pr. 1.5-1.75 M.1.75-2.25
|
Class 1 & 2 Ht..98-1.02 O.1.33-1.66 |
Class 3 & 4 Pr.1.26-1.99 Mr.1.51-2.49 |
Class 3 & 4 Ht.0.91-1.24 Ov.1.26-1.74
|
Emerald and Radiant Cut
Diamonds
| KEY FACTORS |
Class 1. Premium Cut |
Class 2. Fine Trade Cut |
Class 3. Average Cut |
Class 4. Below Average |
| Table Size |
60%-64.1% of diameter |
58%-69% |
53%-76%
|
Below
53%
Above 76% |
| Depth |
60%-65%
of diameter |
58%-69% |
56%-78% |
Below
56% Above 78% |
| Crown
Height % |
11.9%-15% |
11.1-16.2% |
8.5%-18.5% |
Below
8.5% Above 18.5% |
| Girdle Thickness |
thin-med or med.-thick |
thin-thick |
very
thin to very thick |
extra
thin to extra thick |
| Polish
& Symmetry |
good -
excellent |
fair-good |
fair-good |
poor to
fair |
| Length-Width Ratios |
Emerald
Cut: 1.26-1.99 |
|
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There
are other grading systems such as "A, B and C" and a large variety of opinions
that align loosely with the above charts. We have used diamond appraisers
manuals to prepare these charts, so consider them relatively accurate.
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next to Diamond Caret Grading |
