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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 accurate.(Go next to Diamond Caret Grading) | 
