There are a number of instances in the paper where references are made to diamond performance or appearance based on percentages or preconceived trade based ideas of how a diamond should look, or what proportions are considered ‘acceptable’. On page 220 they state “For example, we downgraded diamonds with pavilion angles that were very shallow or very deep because these proportions generally changed the face-up appearance of the diamond in ways that made it less desirable to experienced trade observers.”

The findings of this GIA study, and other studies and approaches to cut grading, will fundamentally change industry expectations. If part of the purpose of this GIA article is to change those preconceptions to match the findings of human observers and the realities of the laws of physics, why be considerate of preconceived trade customs and opinions? As Paul Slegers says, we should not be led by logic dictated by adages like “my child is beautiful”. This would lead to a lost opportunity to take full advantage of the laws of nature to maximise both the beauty and the yield on each and every one of those “finely crystallized carbon” creations.

Paul also notes that trade observers are educated in a certain way of looking, judging and thinking. No matter how ‘blind’ you make their observations by not giving them any parameters before judging, they can identify certain parameters and they may inevitably be influenced in their observational judgements.

This GIA observation based study used diamonds with considerably different weights and diameters; I believe it is un-reasonable to compare diamonds with noticeably different diameters. Diameters were not published, but by estimation with DiamCalc using published proportion data, they ranged from approximately 4.7mm to more than 6mm.  Some of the 15 example stones included heavier diamonds that had larger spreads, and some of the deepest diamonds had the lightest weights.

There appears to be no part of the study that included apparent or observed differences in spread. Stones like RD11 in Cat. 3 and RD33 in Cat. 4 would appear significantly smaller than their measured diameters because of greater upper girdle leakage. In my experience this is a major factor in diamond desirability; it would result in diamonds of these grades being rejected in favour of stones with a lower GIA grade but larger apparent size.

For all practical purposes, GIA has designed a 4 Category grading system. The fifth Category may only apply to the worst 1% of certified diamonds. It could be argued that there is a larger percentage of overly deep uncertified ‘promotional’ grade diamonds, but one can not help wondering if this category was set to appease some sectors of production and wholesale within the industry? Does it serve retailers and consumers to propose an irrelevant fifth grade when there are stones in the fourth category that could already be considered by many as only a little better than unpolished rough diamonds? Cut quality is confusing and creates doubts in consumer’s minds. Doubts are impediments to buying; that inevitably reduce the growth of diamond jewelry as a whole. Brighter, more firey and sparkly diamonds sell themselves and keep customers coming back for more.

It would appear the basis of the GIA grading system will be the proportion data from a scan. Such a system can be described as a parametric grading system that employs look up charts similar to HCA (but with additional minor facet proportions and symmetry and polish grades). The AGS will shortly introduce a more advanced system using parametric and direct assessment techniques. Neither system appears to account for differences in diamond size and accompanying effects on appearance. Neither system is readily functional for the designing and planning of polished diamonds by the scanning software that is widely employed in the industry for rough diamonds. The manufacturing industry will discover that adapting to these new grading systems is rather difficult. OctoNus is continuing with the development of a 3D software based grading system. This system will account for diamond appearance based on size differences, the same system will work for any shaped diamond and it will function in reverse by enabling the best yield planning and the production of rough diamonds into the most attractive gem possible. Eventually this approach to cut grading could do away with the encumbrance of predetermined faceting arrangements; imagine non symmetric one of a kind diamonds with optimal beauty?