Diamonds | Ideal Cut - Modern Round Brilliant Diamond

Ideal Cut vs Standard Cut Diamond

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. As stated in the previous section, an octehedral rough will yield two round brilliant cut stones. On the one hand, the objective is to maximize carat weight, but in order to do this, compromises would have to be made.

If the 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 with a "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

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.

Fig. 1

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.

Fig. 2

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
Pavillion 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 (Fig 3 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.

Fig. 3

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.

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.