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DIAMOND NEWS: The Unkindest Cut
Will the trade listen to Gary Holloway on problems with diamond cuts?
By Damon Poeter

Story illustration Garry Holloway is a man on a mission. The steady, soft-spoken Australian thinks the industry is going about diamond cut grading all wrong. "One of the concerns I have is that a lot of the stones that are on the market at the moment aren't Ideal cut. Not only are they not Ideal cut, they're really lousy cut".

Holloway made this bold assertion in 1999 in the Diamond Cut War Room at the GIA Symposium. Two years later, GK Magazine spoke with him about what he's been doing about the problem in the interim. It turned out to be quite a bit.

Holloway's interest in the quality of diamond cuts began in 1984 when he acquired a Firescope, a tool for viewing diamonds. With it he says he discovered relationships between facet proportions that simply weren't being talked about at the time. These discoveries, he says, have since been confirmed by "virtual diamond" studies conducted by the GIA and Moscow State University.

Holloway found that Tolkowsky's 1919 standard was just one of a variety of proportions that produce beautiful diamonds. His most controversial findings concern the tolerances diamond grading labs apply to Tolkowsky's famous "ideal." He says as cutters attempt to maximize the yield from each piece of rough in order to stay in business, they often cut the steepest crowns and deepest pavilions possible that will still get good numbers on an established grading scale, like that of the AGS.

But the outcome is often disastrous for diamond beauty, contends Holloway (figure 1).

Controversial findings from the GIA's "Brilliance" study (Gems & Gemology Fall 1998) using computer-modeled "virtual diamonds" led to questions concerning the reliance on Tolkowsky's ideal cut. Combinations of proportions with crown angles as low as 23 degrees gave the best brilliance (weighted light return or WLR). These results shook the industry, but confirmed Holloway's observations with his Ideal-Scope (the updated version of the Firescope). Because of this controversy further studies of fire (dispersion) and scintillation are unlikely to be published until the whole GIA study is complete.

In late 1999 a group of scientists from Moscow State University (MSU) posted results of a virtual diamond analysis on www.gemology.ru. These theoretic results for both light return and fire used a more realistic lighting environment than the GIA's model, contends Holloway. They have been combined with equal weighting to give a factor Q (figure 2).

Holloway is convinced that the MSU scientists correctly stress that light return should not be equated with brilliance, though their early results were arrived at before they realized the importance of human physiology and perception. The MSU group is continuing its study, taking people into account this time around.

While research continues, practical applications of the study have already arrived. MSU and OctoNus Software developed DiamCalc (you can download it at www.cutstudy.com), a computer application that creates photo-like images of diamonds that can be tilted in a variety of directions. Holloway thinks the potential for this product is huge, seeing diamond manufacturers using it to design new cuts and avoid "fish-eyes" and "nail heads," as well as visualizing diamonds from Sarin proportions by generating look-alike models. Cut proportion grades are displayed for internationally-recognized standards.

Solution to the diamond cut dilemma?

Garry Holloway thinks the work of a group of Russian scientists has conclusively proven that Tolkowsky's ideal shouldn't be the basis for cut grading.

Figure 1.
Tolerances of a number of grading systems based on Tolkowsky's 'ideal' have been disastrous for diamond beauty, says Holloway. HCA scores and comments show the performance of the worst proportions in the top grades in use today.

Grading System Cut Advisor Score Top Grade Maximum Table Size Top Grade Maximum Crown Angle Top Grade Maximum Pavilion Angle Cut Advisor Comments
AGA 1.5 58.0 34.7 40.8 Excellent
AGJ 4.8 58.0 35.0 41.3 Good
AGS 5.7 57.5 35.8 41.2 Fair
AGT 1.8 60.0 35.0 40.7 Excellent
CGT 4.8 58.0 35.0 41.3 Good
EGL 2.5 57.0 35.0 41.0 Very Good
HRD 8.1 66.0 37.7 42.2 Poor
IGI 6.6 60.0 36.0 41.3 Poor
Russian 7.9 62.0 35.0 41.5 Fair
Scan DN 9.3 65.0 39.0 42.0 Poor

Figure 2.
The MSU cut quality function Q combines results of theoretic studies of light return and fire. Results for light return (not to be confused with brilliance) tend to be higher in the upper left of the chart, while results for fire tend to be higher in the lower right. A Tolkowsky virtual diamond is given a value of 1. The white line shows Holloway's analysis of the GIA's maximum light return for crown and pavilion angle combinations. The red boxes show the weakness in basing standards on tolerances applied to Tolkowsky's proportions.

Figure 3.
Holloway says the weightings for the Holloway Cut Adviser are 'holistic,' whereas other systems fail to recognize the co-dependency of most diamond proportions.

Factor Score Excellent Very Good Good Fair Poor
Brilliance 0-4 0-0.8 0.8-1.6 1.6-2.4 2.4-3.2 3.2-4.0
Fire 0-2 0-0.4 0.4-0.8 0.8-1.2 1.2-1.6 1.6-2.0
Scintillation 0-2 0-0.4 0.4-0.8 0.8-1.2 1.2-1.6 1.6-2.0
Spread 0-2 0-0.4 0.4-0.8 0.8-1.2 1.2-1.6 1.6-2.0

Total Score 0-10 0-2 2-4 4-6 6-8 8-10

Figure 4.
An example of DiamCalc virtual diamonds, with representative cut flaws at various meetings of the crown and pavilion angles. The software, created by researchers at Moscow State University and OctoNus Software, creates photo-like images of diamonds that can be tilted in a variety of directions. Holloway believes this application has the potential to revolutionize the way we go about cutting and buying diamonds.

The Holloway Cut Adviser

Holloway has developed what he calls the Holloway Cut Advisor (HCA), available at Pricescope.com. The following is his description of what it can do, its uses and the methodology behind it:

The HCA rates four factors diamond shoppers look for: brilliance, fire, scintillation and spread.

Brilliance is thought of as the proportions that reduce light loss from the pavilion (bottom) of a diamond. But understanding brilliance involves other factors like the directions in which light travels to an observer and the source and type of light. The effects of scintillation and the background from which a flash of white light or fire is displayed complicates matters further.

Fire is the spectral separation or dispersion of white light into rainbow flashes. The direction, spread, size and intensity of fire are complex.

Scintillation might be described as the 'bang bang' of contrasting dark and bright areas as the diamond is rocked from side to side. The even spacing of a good balance of blackness makes white or colored flashes appear to sparkle more. A good analogy is black opal, which is more striking than an equally colorful white opal.

Spread is a factor that has been ignored in other grading systems. It is the simplest and too many people the most important "desirability" factor. The apparent size of a diamond is also compared and rated.

Observations of actual diamonds - especially using the Ideal-Scope - and comparative studies with DiamCalc were used to calculate the values for HCA. By comparing virtual diamonds, I was able to eliminate variations in color, clarity, symmetry etc. encountered in real diamonds. Ray path analysis was also used extensively.

The HCA identifies three categories of diamonds with optimum beauty:

  • Brilliant Ideal Cuts [BIC's] return the most light, especially in office-type lighting. BIC's have the largest spread for the same weight. Fiery Ideal Cuts [FIC's] have more fire, especially in spot lit environments. They also appear to have more facets and scintillation because the steeper crown facets provide more interaction with pavilion facets. Although these diamonds are hard to find, I think romantic aesthetes tend to prefer FIC's even though they are smaller and a little less brilliant.
  • The Tolkowsky Ideal Cut (TIC) combines a good balance of fire and brilliance when HCA standards are applied. But beware of steep/deep diamonds with near Tolkowsky proportions, because they will have a dead dull area just inside the table that really lets the side down when the diamond is dirty. Diamonds close to Tolkowsky proportions cost a lot more, and in my retail experience I've found there is actually more demand for BIC's because of both cost and spread.
  • Separating diamonds with excellent proportions into BIC, TIC and FIC grades will assist cutters and dealers to meet differing geographic and socio-economic demand. Markets will establish pricing information based on this knowledge.

The Future

Holloway's ongoing study includes the effects of the minor facet groups of upper crown and lower pavilion girdle facets as well as symmetry. He says excellent results can be achieved by "tweaking" these minor facets and is looking forward to a consulting career working with diamond cutters to improve both yields and prices at the same time. "One cutter listened to me last year and tells me every stone they cut to my standards is the first sold from the parcel. He now has hundreds of old stock 4-grainers and wants to know if he could just re-cut the crown or the pavilion and not the whole stone.

Pricescope.com is a price comparison search engine similar to RapNet and Polygon except it is for consumers. Holloway collaborated with Pricescope.com's Leonid Tcharnyi's to create a diamond tutorial for consumers and plan to offer a subscription paying full diamond buying course on line for consumers and another to train e-tailers and retailers in how to handle the knowledgeable consumer.

The website allows surfers to compare loose diamond prices from over 50 e-tailers, some of which are vendors of their own stock, but most stones come straight off RapNet and Polygon. Holloway says the HCA service has attracted tens of thousand users since its debut in November 2000. In that short space of time cutters and Web vendors have begun asking how to improve the HCA ratings of their goods. Holloway grins at this and says, "It's working, and now they will improve their make.

A detailed paper revealing the mechanics and methods that underpin the HCA is being reviewed for publication by a major gemological journal.