In 1919, Marcel Tolkowsky, a member of a Belgian family of diamond cutters, published Diamond Design, the first recorded analysis of diamond proportions for the round brilliant cut diamond. His work was based on modern theories of light behavior and his opinion of what proportions resulted in what many industry professionals considered to be the best possible balance of brilliance and dispersion of light until the late 1990's.

Tolkowsky’s calculations indicate that for optimum brilliance a round brilliant cut diamond should be cut to the following angles and proportions:

• 34.5° Crown Angle.
• 40.75° Pavilion Angles.
• 59.3% Total Depth (excluding girdle thickness) with 16.2% of the depth being comprised of the crown (top half of the diamond) and 43.1% representing the pavilion lower half of the diamond.
• 53% Table based on diamond's overall diameter.

Tolkowsky's design is frequently referred to as the "American Ideal Cut" because diamond cutters in the United States began cutting it first. Marcel Tolkowsky's early model of brilliance set the stage for the modern AGS Ideal Cut Diamond and Hearts & Arrows Ideal Cut Diamond which are the most brilliant and dispersive diamonds available on the open market today.

Do not be confused or misled by the appearance of the words "Tolkowsky Cut" on some diamond grading reports. The words "Tolkowsky Cut" do not necessarily mean that a diamond has been cut to Tolkowsky's exact specifications. Some laboratories will say that a diamond is "Tolkowsky Cut" or within "Tolkowsky Range" if the diamond's proportions are "within tolerance" of Tolkowsky's original calculations. According to the specifications of one laboratory, "Tolkowsky Range" is as follows:

• 33 - 36° Crown Angle.
• 40 - 41.5° Pavilion Angles.
• 56 - 60.5% Total Depth (excluding girdle thickness) with 14 - 16.5% of the depth being comprised of the crown (top half of the diamond) and 42 - 44% representing the pavilion lower half of the diamond.
• 53 - 57% Table based on diamond's overall diameter.

We have evaluated "Tolkowsky Cut" diamonds that scored overall proportions ratings as low as AGS-2 Very Good on our Sarin DiaPort computerized proportions analysis machine. Recently we have even seen the words "Tolkowsky Cut" used on some lab reports to describe the overall proportions rating of fancy shape diamonds such as Flanders Brilliant, marquise, and princess cut diamonds... What gives with that? How is it possible that the results from Tolkowsky's analysis of the modern round brilliant cut diamond can be applied to a diamond with a completely different shape and facet structure?
"Ideal Cut" vs. "Ideal Range"

To the average consumer, the terms "Ideal Cut" and "Ideal Range" might seem like the same thing, however they are actually quite different. Understanding how these terms are used and misused by the diamond industry will assist you in the selection process of your diamond and possibly prevent misunderstandings.

A true "Ideal Cut Diamond" is a round brilliant cut diamond that has been cut to AGS Ideal Cut Proportions as defined in the following table:

• Table Diameter     52.4 - 57.5%
• Crown Angle     33.7 - 35.8°
• Pavilion Angle     40.2 - 41.2°
• Girdle Thickness     Thin, Medium, Slightly Thick
• Culet Size     None, Pointed, Very Small, Small, Medium

"Ideal Range" refers to round brilliant cut diamonds that have been cut within a range of variables similar to, but not as exacting, as Marcel Tolkowsky's original calculations and outside the parameters of "Tolkowsky Range" mentioned previously. Diamonds cut within the "Ideal Range" are neither as brilliant nor dispersive as those cut to AGS Ideal Cut proportions.
Many "industry professionals" would agree that the following proportions are within the "Ideal Range" for a round brilliant cut diamond:

• 31.7 - 37.3° Crown Angle.
• Pavilion Depth of 41.2 - 44.8%.
• 52.4 - 63.5% Table Diameter based on diamond's overall diameter.

However on the AGS Proportions Scale a diamond with a 63.5% Table Diameter would score no higher than AGS-3 Good. Considering that a round brilliant cut diamond with a proportions rating of AGS-4 Good has an average light return of 70% and an AGS Ideal Cut Diamond has an average light return of 96% wouldn't you rather buy a real ideal cut diamond and not one that fits within the industry's catch-all range of ideal? After all, the proportions of a diamond control 98% of it's brilliance and dispersion. The closer you come to finding a diamond with true ideal cut proportions, the brighter it will be and the more fire it will have. For those of you who truly seek diamonds with incredible brilliance and fire, you will find them within our Private Reserve where all of the round brilliant cut diamonds listed have True Ideal Cut proportions and have been carefully selected for their brilliance.