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Diamonds: Ideal Cut - Modern Round Brilliant Diamond

Triple-0 Round Brilliant Cut Diamond

Ideal Cut vs Standard Cut Diamond

Article Copyright © 2009

When deciding how to cut a rough diamond, a cutter must make a cost-benefit analysis as to how to maximize the cut stone's value. An octehedral rough diamond will yield two round brilliant cut stones (see diagram below). The objective is always to maximize carat weight, but in order to do this, compromises would have to be made.

The clarity of the stone, and the amount of internal inclusions will play an important part in the decisions as to how to maximize yield. This is accomplished by reconciling three key factors - weight retention, cut proportions, elimination of any inclusions.

Reconciling Cut & Weight Retention

If the rough stone has a colorless D through F rating and has very few inclusions, it would be cost effective to sacrifice some carat weight in order to finish with two "Ideal" cuts. If, on the other hand, the rough stone has some coloration and/or is heavily included, it may be better to aim for a higher carat weight utilizing a "Standard" cut.

Ideal vs Standard Cut

Parameters Ideal Cut Standard (Premium) Cut
Rough Material Loss Greater Loss Higher Yield
Finished Stones Lower Carat Weight Higher Carat Weight
Cutting Time 2 to 4 Days 1 to 2 Days
Crown Symmetry Ideal Shallow Crown
Pavilion Symmetry Ideal Deep Pavilion
Girdle Symmetry Ideal Thick Girdle

When dealing with a near-perfect (or flawless) stone the cut that is generally preferred is the classic "round brilliant" cut. This is primarily due to the fact that this cut has yet to be improved on for two reasons: 1. it is the most efficient cut for maximizing yield, and 2. it is the best cut for showcasing a high-quality stone's fire and brilliance. This is why it is very rare to see flawless stones cut into fancy cuts such as emeralds, hearts, etc.

The Modern Round Brilliant Cut

The modern "Round Brilliant Cut" (below) was developed by Belgian diamond-cutter Marcel Tolkowsky in 1919. This cut is also known as the "Tolkowsky Cut" and "Tolkowsky Brilliant." Even with modern techniques, the cutting and polishing of a diamonds resulted in a loss of as much as 50% of the stone's total weight. The round brilliant cut was a partial solution to this problem. The round brilliant cut is beneficial when the crystal is an octahedron, as two stones could be cut from one crystal.

Diamond Brilliant Cut Diagram - Table & Crown

In the diagram of a "Round Cut" diamond (above and below), you will see that there are 8 "star" facets, 8 "kite" facets, 16 "upper girdle" facets, 16 "lower girdle" facets, 8 "pavilion" facets, 1 "culet" facet on the bottom, and one "table" facet on the top of the stone for a total of 58 facets.

Diamond Brilliant Cut Diagram - Pavillion

An "Ideal Cut", "Premium Cut" or "Modern Round Brilliant" (Tolkowsky Round Brilliant) diamond as shown in the diagrams above would have the following basic proportions according to the AGS:

  • Table Size: 53% to 57% of the diameter
  • Total Depth: 58% to 63% of diameter
  • Crown Angle: 34 to 35.5 degrees
  • Pavilion Depth: 42.5% to 43.5%
  • Girdle Thickness: medium to slightly thick
  • Culet: pointed, very small to small

In the 1970s, Bruce Harding developed new mathematical models for gem design. Since then, several groups have used computer models and specialized scopes to design new diamond cuts.

Tolkowsky, Eppler & Scan D.N.

Variations on the Tolkowsky Brilliant (diagram below) are the "Eppler" (European Practical Fine Cut, or Feinschliff der Praxis) with a table width of 56%, crown height of 14.4%, and overall height of 57.7%. The "Scan D.N." (Scandinavian standard, or Scandinavian Diamond Nomenclature) diamond cut has a table width of 57.5%, crown height of 14.6% and overall height of 57.7%. Other variations of the MRB include the "Ideal Brilliant", invented in 1929, the "Parker Brilliant" invented in 1951, and the "Eulitz Brilliant" invented in 1972.

Tolkowsky, Eppler & Scan DN Cuts

To quantify a diamond's cut quality, gem labs will use a variety of equipment such as a BrilliantScope, H&A Viewer, Ideal Scope, Sarin Diamension and/or FireTrace.

D-Flawless Brilliant Cut Diamond

AGS Triple Ideal or 'Triple 0' Grade

The AGSL grades a diamond's cut quality using three parameters: Polish, Symmetry, and Proportions. Each parameter is given a 'grade' from 0 (Ideal) to 10 (Poor). When all three parameters are in perfect harmony the diamond is given a "Triple 0" or "Triple Ideal" grading. The AGSL grades a diamond's symmetry and proportions according to where facets intersect, and crown/pavilion angles, but does not measure or quantify relative facet angles and/or individual facet ratios. A perfect blending of facet symmetry, facet ratios, and facet angles will yield a perfect 'Hearts & Arrows' Diamond pattern when viewed through a H&A Viewer.

As with all human endeavors, there is a constant attempt to 'build a better mousetrap;' and there has been numerous attempts to improve on this tried-and-true formula with the introduction of new signature diamond cuts that claim to have a higher light return, more brilliance and fire, etc.. Producers split hairs over cut angle, cut proportions, and number of facets, but at the end of the day it may simply come down to consumer preference and/or marketing. One thing is for sure - like Einstein's theory of relativity, Tolkowsky came up with a "brilliant" idea almost 90 years ago, and it still survives in some form today.

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Bibliography on Brilliant Diamond Cuts

1. Marcel Tolkowsky, Diamond Design .

2. Sarin, Diamond Grading . Sarin Gem Labs

3. HCA IdealScope, Hearts and Arrows .

4. GIA, Gemological Institute of America .

5. AGS, American Gem Society - Diamond Grading .

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