The Ideal Cut

"The pursuit of perfection is a human calling. The diamond – already perfection in the eyes of most – has been cut and shaped in an ever–changing variety of ways since modern cutting techniques were invented, all in an effort to maximize its full potential for brilliance."

Predecessors of the modern round brilliant, such as the European or Old Mine cut, were fairly deep stones with very small tables, large culets and short pavilion facets; there was no single standard way of cutting them and diamonds from that time therefore vary widely in appearance. However, in 1919, diamond cutter Marcel Tolkowsky published a doctoral dissertation that would change all of that. Using only his own visual assessments of different variations of diamond cuts, he presented a theory about the cutting angles which would create the most proportionate balance of brilliance and dispersion in a gem–quality diamond. Tolkowsky's measurements for achieving the "Ideal Cut" were exact and strict: a 34 1/2º crown angle with a 53% table, which created a 16.2% crownheight; and 40 3/4º pavilion angle combined with a 43.1% pavilion depth. Improved cutting techniques and technology which were being developed at the same time finally allowed cutters to achieve these more precise and stream–lined designs.

Despite Tolkowsky's theories, opinion regarding diamond proportions was not unanimous. Tolkowsky's measurements were eagerly adopted and adhered to by the American Gem Society (AGS). However, by the beginning of the 1950s, a backlash had begun and diamond cutters increasingly moved away from the ideal cut and toward diamonds with shallower crown angles – angles as low as 32 1/2º – and larger tables of 60% and even 64% or 65%. Many went so far as to argue that the proportions of the Ideal Cut created an inherent over–abundance of dispersion, or "fire," which distracted from the diamond's brilliance. As proof that the Ideal Cut was not an absolute embodiment of perfection, they pointed to Eastern cultures, which actually considered larger tables more beautiful than the smaller ones which typified an Ideal Cut. Even those who embraced the Ideal Cut realized the impracticality of cutting diamonds to such a specific set of parameters and soon modified its definition by expanding the acceptable table size from Tolkowsky's original 53% up to nearly 58%.

Against this backdrop of disagreement, The American Gem Society (AGS) opened its own lab in 1996. They sought to bring the public trust into their camp by providing independent documentation to confirm the superiority of the Ideal Cut. To accomplish this, the AGS began to grade and certify cut and proportions – something that had previously not been done by other labs. These grades were based on how closely a given diamond's cut conformed to the standards established by the Ideal Cut. The grading scale ranged from 0 (the finest quality) to10 (poor quality). Diamonds that fell within the Ideal Cut range were, of course, graded as 0. AGS's influence on the Ideal Cut's rise in popularity is evidenced by the fact that, today, the term "AGS zero" is synonymous with the Ideal Cut.

By the time the AGS Lab opened its doors, the Ideal Cut was no longer conceived of as only the single set of proportions set forth in Tolkowsky's original dissertation. Rather, it was regarded as a design based on a narrow range of combinations of proportions. " (Source: "The Ideal Cut: A Consumer's Guide")

The range is:
Table Diameter: 52.4% to 57.5%
Crown Angle: 33.7 degrees to 35.8 degrees
Girdle Thickness: Thin to Slightly Thick (.51% to 2.95%)
Pavilion Angle: 40.2 degrees to 41.25 degrees
Culet: None (Pointed) to Medium
Total Depth: 56.88% to 63.92%

How are a Diamond's "Proportions" Measured?

A precisely–tuned instrument called a Sarin Dia Mension proportion grading machine can be used to measure a diamonds proportions. The Sarin Dia Mension is used by AGS.
No machine can measure a diamond's quality of finish. The AGS 0 cut grade also means that a diamond possesses ideal symmetry and polish.

However, in recent years the term "ideal cut" has been adopted by many jewelers, especially on the internet, to loosely describe any diamond that falls within these "general" cutting parameters, or has a small table. Beware of claims of "ideal cut" without documentation of the diamond's specific proportions, e.g., crown and pavillion angles. You may end up paying a premium for a diamond that really isn't "ideal cut". Technically, Ideal Cut is a brand name for diamonds that both fall within the Ideal range and are accompanied by an AGS certificate or at a minimum a Sarin report.

Recent research suggests that while the Ideal Cut has grown in popularity and draws a premium price, it is really just a matter of personal opinion. Many combinations of cut proportion can produce a brilliant, firery diamond, while at the same time, cutting flaws can drastically detract from a diamond's ability to refract light. Ensure the diamond seller you deal with can discuss the exact diamond proportions with you and has the documentation to illustrate all the cut proportions.

GIA Researchers Conduct Study on Round Brilliant Cuts
"Researchers at the Gemological Institute of America (GIA) concluded from the results of a study on diamond cut that there is no single best set of proportions for a round brilliant diamond that maximizes fire. The results appear in an article titled 'Modeling the Appearance of the Round Brilliant Cut Diamond: An Analysis of Fire, and More About Brilliance,' published in the Fall 2001 issue of Gems & Gemology. The results of the study also shows that the lengths of star and lower–girdle facets are critical to cut assessment in round brilliants, even though no current grading systems factor these aspects into their analysis." (Source: Rapaport Diamond Report, January 4, 2002).
If you're considering an "Ideal Cut", remember that, while they are exceptional, they are generally also more expensive. Be prepared to spend a little more for an Ideal Cut than you will for a comparable diamond that is not graded as Ideal. In all circumstances, beware of jewelers who describe as "ideal" any diamond with Ideal proportions but without high–quality finish or specific documentation on cut proportions.

If you're not sure about the added cost of an "Ideal Cut" and are concerned that a diamond with a larger table might somehow look 'less beautiful' than a diamond with a smaller table, consider the true difference between two table sizes: in a 1 carat diamond, the difference between a 57% "ideal" table and a table of 59% (which is just outside the traditional ideal range) is a mere 0.13 millimeters – this is just slightly more than the thickness of a single human hair! And while the difference between a 57% table and a 62% table might sound dramatic, even this represents a difference of less than 0.30 millimeters. These subtleties are very hard to detect with the human eye, and to some people, such subtleties are not worth the added expense that buying an Ideal Cut.