An ideal cut diamond for every preference

As you learned in Standards for Ideal Cut Diamonds, there are a wide variety of diamond proportions which have been considered to be “ideal cut” over the years, and the American Gem Society Laboratory (AGSL) is the only gemological laboratory who uses the term ideal cut to describe the highest cut grade available from their laboratory.

Thus it is important to be fully aware of how an ideal cut diamond is being described, because clearly there are different qualities of ideal cut diamonds available to choose from, there is also a wide variance in the degrees of light return and sparkle factor provided by different ranges of ideal proportions deemed to be acceptable by the AGS Laboratory.

This proportions chart published by the AGSL in 2008, shows the range of range of proportions grades available for a round brilliant cut diamond with a table diameter of 55%, there is a different chart available for diamonds with a table diameter ranging between 52% to 65%, and the range of crown and pavilion angle for the AGS Ideal Cut proportions grade changes in conjunction with the table diameter measurement.

Thus determining whether a diamond is “ideal cut” by the standards set forth by the AGSL, is no longer as simple as ensuring that it has the right crown and pavilion angle, it has to be the right crown and pavilion angle for a diamond with that table diameter. The offset for crown and pavilion angle that is considered to be ideal for a diamond with a table diameter of 54% may not be ideal for a diamond with a table diameter of 60% and so forth.

Accounting for Personal Preference of Ideals:

One of the reasons why the AGS Laboratory is due to the reality that different diamond proportions, have the potential to produce a similar volume of light return, but different balances of brilliance and dispersion, and different people might find the overall visual performance of each diamond to be appealing based upon their personal preference for brilliance and dispersion.

The range of proportions which Brian Gavin Signature and Brian Gavin Blue (fluorescent) round diamonds are cut to, are based upon Brian Gavin’s personal preference for round brilliant cut diamonds which exhibit a high volume of light return, with a virtual balance of brilliance and dispersion, thus the proportions lean towards the middle of the range of measurements designated for the zero ideal cut proportions rating from the AGSL.

Not surprisingly, the range of proportions which Brian Gavin round brilliant cut diamonds are cut within, is extremely close to the range proposed in Marcel Tolkowksy’s Diamond Design of 1919, and represents the middle of the range designated as the design of the American Ideal Cut diamond, this is because it is the “target range” which has long been recognized as the “sweet spot” which results in diamonds which exhibit the highest levels of brightness, and the best balance of brilliance and dispersion.

While it might be possible for a round brilliant cut diamond with a 60% table diameter with a crown angle of 30.5 degrees which is offset by a pavilion angle of 41.8 degrees, to receive an overall cut grade of AGS Ideal-0 based upon the proportions, the reality is that it will not exhibit the visual performance of a round brilliant cut with a table diameter of 56% which has a crown angle of 34.5 degrees which is offset by a pavilion angle of 40.8 degrees.

The two diamonds will exhibit a dramatically different volume of light return, and different types of sparkle, which the AGS Laboratory believes might be appealing to diamond buyers with different tastes. Arguably, the choice to purchase one “ideal cut diamond” over the other might simply be due to the fact that the diamond buyer who chooses the option with the 60% table diameter has not had the opportunity to compare it to the option which is cut to tighter proportions.

One thing is for certain, the odds are that if you were to compare the two diamonds side-by-side, you would see a distinct difference in the volume of light return and the sparkle factor; it’s a simple matter of geometry.