GIA Ex: Consumers Be Aware - GoodOldGold.com

GIA Excellent Cut: Consumers Be Aware

The following is my response to Garry Holloway’s article featured in the Journal of PriceScope:
GIA Excellent Cut: Consumers Beware

Important Update to this article (8/22/06): We have acquired the test cz stones used in this study and have documented their appearance which, in our opinion, clearly supports our conclusions in this article. I refer to these stones later in this article but here is a direct link to the video assessment of the same two stones used in this study.

Before we get started with this review, just a little background. Garry and I have a rather long history participating on the forums together and have been through quite a bit. Roughly 6 years now. We’ve both been involved in many arguments/debates and have talked both in accord and at times in opposition with each other especially regarding technologies and the information they relay to the viewer. Throughout them all however we have always remained friendly and although I don’t have the time I’d like to read everything he’s published on the forums, I think it is fair to say that not only have I learned from him but him from me as well. When iron sharpens iron oftentimes sparks fly and this instance has proven to be no exception. I need not recount the times I have been railed (not necessarily by Garry) but by others with the most recent research we’ve reported and released regarding our investigations into this most current issue of the GIA DiamondDock™ and it is this article that is being hailed as “the source” for many of these accusations. Hence the need to respond to this in detail.

Also, while I bring up Garry’s name frequently within the article, I realize it will be tough for some not to interpret my words as not being personal. I hope Garry himself knows that I am being critical of the information being presented than in criticizing Garry himself and I realize it is sometimes hard to draw the line between the two so if words come across as I don’t intend, please understand up front that I believe Garry has the best interests of the consumer at heart when he writes or publishes his material. Often when reading critiques on my own work and research, I have this problem sometimes not being able to draw the line between constructive criticism and personal attacks (although both have been hurled my direction over this very issue in recent months). I quote him myself in my own cut tutorial and I would not quote another gemologist/source if I didn’t feel their motives and intentions weren’t pure or had the best interests of the consumer in mind as well as the info being accurate as well. So, my response is not written with a chip on my shoulder or any particular axe to grind. I am just interested in reporting my findings into these issues which in this case runs counter to most of what Garry has said in this article. With this understanding, let’s proceed.

Having spent roughly the last year researching the details that go into determining the grades of both the GIA Cut Grading system and the AGS Cut Grading system and owning the materials used to determine the optical and physical characteristics that go into determining the grades I am finding (as in the case of Garry’s article) some grave misunderstandings being drawn about the GIA system and the materials used (particularly the DiamondDock) which I would like to offer my professional commentary on.

The materials used in our own research of the GIA Cut Grading system are and have been…

· A number of diamonds which fall into various cut grade categories in the newly released system.

Garry’s article is broken down into a number of sections including the introduction/background. In this article I’ll be offering a point by point commentary where I feel it is necessary and a short summary of the chapter towards the end of each one.

Quotes from Garry’s article will be italicized and indented for easy identification (as below).

GIA began a computer ray tracing Cut Study in 1989[1]. In 2001 they were ready to validate computer findings with a human observation survey. But there was only a 58% correlation[2].

· Most of the observations were made by industry participants: only 7% were ‘consumers’. Trade observers could be biased in favor of smaller diameter steep crown - deep pavilion diamonds with better yields & profits.

· The lighting GIA used in the survey skewed observer preferences toward deeper smaller diameter diamonds (commercially favorable).

· Diamonds were shown in a gray color tray; conventional wisdom suggests the tray should have been black. A set diamond has little or no light entering from under the stone so leakage areas look dark.

Pointing out the fact that only 58% of the observers agreed with the ray tracing Cut Study in 1989 does not point to any fact where GIA went wrong. On the contrary it points to true wisdom by turning to human observation testing to confirm if the technology agreed with actual human eye observation. After all, a consumer does not go home with ray trace software, as good as the information that can be garnered from ray trace software, nothing and I repeat nothing supersedes what the human eyes can ascertain about light performance and the characteristics that determine diamond beauty. My personal experience working with optical technologies over the course of the past 6 years has taught me that no matter how good any certain technology may be, each exhibit weakness’ as well as strengths as there is generally some element that does not correspond with human observation. It is our professional opinion that human observation takes precedence over technology and not vice versa as it is human observation that reveals the flaws in any given technology.

While trade observers “could be biased”, the trade observers were not privy to exact detailed characteristics of the diamonds they observed so there was no foreknowledge of which diamonds were apparently cut better than the others. On top of this the trade observers were not viewing the subject diamonds in their normal viewing conditions. Normal viewing conditions for most folks in the trade is under a day light fluorescent desk lamp and holding the subject diamond in a pair of tweezers, and usually against a bright white backdrop such as depicted in the following graphic.

GIA’s suggested lighting environment could indeed include the environments depicted above however with one primary difference. That being the addition of a neutral colored backdrop instead of bright white. Why? Two very logical reasons.

1. Observing poorly cut diamonds with excessive leakage against bright lighting with the combination of a bright white background can make a poorly cut diamond appear better than it will in many common viewing environments that do not have such bright backgrounds. By eliminating the bright white background, this misleading view is neutralized by viewing the stone against a neutral background and shows the diamonds brightness for what it really is … mediocre (if it is indeed so). We have demonstrated this in our video on the subject as read and featured as the subject content of this thread. As you can note the more poorly cut stone appears to have a lighter appearance against the white backdrop. Eliminate the white backdrop and replace it with a neutral color and one can see quite easily that the poorly cut stone actually lacks brightness in an easier fashion and the viewer is not misled.

2. The second logical reason for using neutral colored backdrop is because when a diamond is mounted in a ring, virtually 99% of the time the diamond is against a neutral backdrop such as the metal behind the diamond or the skin of the person, all which are neutral colors.

So without any foreknowledge of the cut details of the diamonds being observed, the observers themselves were asked 4 basic questions as they were viewing the diamonds in diffuse daylight fluorescent lighting, led spot lighting and a combination of both with a neutral colored backdrop.

Regarding the observations between consumers and trade people, GIA found there to be direct correlation between what consumers considered most bright/fiery/scintillating vs tradesmen since the tradesmen were not privy to cut data but were only judging face up brightness/fire/scintillation and not proportion factors.

· The lighting GIA used in the survey skewed observer preferences toward deeper smaller diameter diamonds (commercially favorable).

During our research on this subject of the lighting environment we took it upon ourselves to purchase the exact lighting environment GIA used in their observation testing. That environment is found in the GIA DiamondDock™. Our personal experience with the DiamondDock shows us that there is absolutely no skewing of preferences to make deeper smaller diameter diamonds appear better as Garry says. These differences in appearance can easily be seen in our video on the subject. In fact it matters not what diffuse day lighting the observations are made in. The same conclusions are drawn about the comparison stones which any layman can see both in person and via the video. As this article goes to publishing on the forum, the subject video demonstrates this point rather clearly.

Here is a photograph taken under DiamondDock lighting showing the comparison Garry is talking about of a deeper smaller diameter diamond (commercially favorable) on the right alongside a GIA Ex on the left. Every person we show this comparison to does not favor the deeper smaller diamond as Garry suggests. In fact I can say this comparison is drawn 100% of the time which is why I don't quite understand the reason for Garry's statement.

Since writing this article we have also come to learn that Garry's main point of contention is that the DiamondDock lighting is making commercially favorable steep/deep diamonds (like that on the right above) appear brighter than shallow angled diamonds. While we see a degradation of optics in shallow angled diamonds (also seen in the following graphic) and both GIA and AGS agree that shallow angled diamonds do not deserve their top grade, the DiamondDock lighting does not do what Garry is claiming either regarding this comparison. In the photograph below the shallow angled diamond is on the left and the commercially favorable steep/deep is on the right. While there are areas of unwanted darkness within the shallow diamond on the left, we actually stand in agreement with Garry's personal taste when it comes to shallow diamonds vs steep diamonds. Ironically DiamondDock lighting demonstrates the point rather well too! In the shallow vs deep debate the DiamondDock demonstrates good reason for Garry's personal preference towards these diamonds.

Garry seems to take issue with the DiamondDock when in fact GIA encourages gemologists to use any available diffuse day light source. In our lab we have done just this and as presented in the video on Brightness (and our soon to be released video on Fire) the same conclusions are drawn in various environments using a steep/deep cut diamond (the type of stone Garry is saying the DD skews observer preferences on). The primary difference between these environments is the intensity and positioning of the light sources, however any layman can see which of the 2 diamonds is exhibiting less brightness than the other in each environment. So Garry’s point seems to suggest that all diffuse day lighting environments are fine to look at diamonds under except GIA’s!? We have found the lighting environment to be perfectly normal and representative of what a consumer can expect to see when viewing a diamond in normal day light environments. Consumers have also confirmed this as well both locally and abroad.

Having shown diamonds for the past 25 years and before the release of GIA’s DiamondDock™ we have found that conventional wisdom dictates a neutral colored background for the observation of loose diamonds 99% of the time. Contrary to Garry’s statement, 99% of set diamonds (at least in the United States) do indeed allow light to enter from under the stone since most engagement ring diamonds are set into prongs or some type of setting wherein light and/or neutral colors can reflect into the pavilion of the diamond. When a diamond is set into prongs or the like you have the neutral colors of skin, metal along with light that enters through the pavilion of the diamond. Conventional wisdom actually suggests that an observer view loose diamonds against a neutral colored back drop and not black.

In fact GIA did indeed use various types of backgrounds in their observation testing and experimented with a black tray. Overall they felt the neutral gray represented the most accurate view to real world appearance of diamonds and is why this is the color they ultimately chose to use. Neither did they find a bright white background to be as accurate either.

· Dark black backdrops cause an enhanced-darkness under the tables of diamonds exhibiting mild leakage under the table which is not visible to human beings using both eyes (stereo vision).

· Bright white backdrops cause these types of stones to appear brighter than they normally would, including diamonds that would exhibit excessive leakage under the table and around the upper half region.

There is one exception however wherein a person might want to consider viewing a diamond against a black background and that is if they are having a diamond set into a bezel type mounting which does not allow any light to enter through the pavilion and is generally all dark underneath the diamond. If you are one of the few people mounting a diamond into a bezel mounting, then there are certain combinations of GIA Ex cut grades you may not want to consider.

In Garry’s article he reports the observations of 3 people viewing the following 3 diamonds in natural daylight environments. The table below is the reported specs on each of the diamonds.

Three GIA Cut graded diamonds were photographed in GIA’s Diamond Dock® light box. One was Very Good and two were GIA Excellent.

*Specimen*	A.	B.	C.
*Carat/Color/Clarity*	1.16 G SI1	1.19 G VS2	1.28 G VS1
*Diameter*	6.85mm	6.75mm	6.92mm
*Table / depth %*	60% / 58.9%	55% / 62.7%	57% / 62.9%
*Crown Angle*	33°	34.5°	35°
*Pavilion Angle*	40.6°	41°	41.4°
*Girdle[i]*	medium to slightly-thick	medium to slightly-thick	medium to slightly-thick
*Star / Lower Girdle %*	50% / 80%	45% / 80%	45% / 80%
*GIA Cut Grade*	Very Good	Excellent	Excellent
*AGS Light Performance*	3	0 (Ideal)	2
*DiamCalc Light Return*	.96	.99	.88
*DiamCalc Contrast*	.93	.99	1.01
*DiamCalc Spread*	+3%	-3%	-5%
All stones were graded by GIA: Very good or Excellent for Symmetry and Polish. None for Fluorescence Stone A has Painted Upper Girdle Facets

Figure 1. shows a young grade using GIA’s Diamond Dock® lighting box. The tray is actually the same shade as the body of the box, but appears lighter because of its proximity to the two 15 watt high color temperature florescent tubes. There are two switches on the upper right for these tubes and / or 12 LED lights (which are not turned on, also this photo was taken with flash).

In this photograph the grader is not actually viewing the diamonds as GIA suggests. GIA’s suggestion is viewing the diamonds towards the bottom of the DiamondDock and bringing your eyes into the proximity of their focal length when normally viewing diamonds. On a personal note we have been able to see and detect decreases in optics with the tray from the bottom up to around half way up in the DiamondDock (similar to the above photograph).

Next Garry attempts to discredit the backdrop GIA suggests when viewing the loose diamonds when in fact his own photography suggests otherwise.

1. Effect of the tray on diamond appearance.

Figure 2 shows three GIA graded diamonds photographed in GIA’s Diamond Dock light box resting on various backgrounds: white, GIA’s gray tray and black. The stone (A) on the left is shallow, the center stone (B) is close to Tolkowsky ‘ideal’ proportions and the stone on the right (C) is deeper.

Figure 2. Specimens from Table 1 photographed in Diamond Dock® on different backgrounds (trays)

Note that the GIA gray tray provides the best appearance for the deeper stone (C). The black background is the worst for this stone as most of the table area is dark.

While we would certainly agree that the black background is the worst viewing environment for stone #3 blatantly showing the leakage (good for a critical exam), to state that “the GIA gray tray provides the best appearance for the deeper stone (C)” is in our opinion a false dichotomy. We ask you the reader … which photograph makes diamond C appear brighter? It is our contention that the white tray makes diamond C appear brighter and darker in the gray tray. What do you think?

Diamond C against white backdrop	Diamond C against gray backdrop

While this evidence from Garry’s own photography plus the one we provided above of the deep/ideal comparison is enough to rest our case about the background, let’s examine the rest of his arguments. Interestingly Garry’s photography proves the points we brought out above for the logical reasons of using a neutral colored backdrop. One other point of note with DiamondDock viewing is Garry’s test diamonds in the gray tray are laying in GIA’s tray with the girdles below the cut outs. This is not recommended as the girdle planes should be resting at or above the cutouts.

In the next section Garry shows the Ideal-Scope images and ASET images of the 3 test stones.

Figure 3. Ideal-scope (top) and AGS ASET (bottom) images of the diamonds from Table 1

The shallow VG stone (A) shows too many dark zones in the ideal-scope[4] and too much blue through ASET. The ‘ideal’ stone (B) has excellent Ideal-scope and ASET images, deserving of its Excellent cut grade. The deep GIA Excellent stone (C) has a lot of leakage just inside the table, and the dark or blue star pattern is weak in Ideal-scope and ASET images respectively. This stone has a very good DiamCalc™ contrast score (1.01), but because the stone is large enough for the leakage zone (contributing to the stones contrast score) to be visually seen as a circular dark zone, I believe the contrast result is misleading.

While we have not arrived at any concrete conclusions regarding DiamCalc/Gem Advisor scores we have seen interesting correlations between MSU’s contrast score in relation to human observation testing of such diamonds. That correlation can be seen in our own observation testing with a similar type of stone to Garry’s here and when Leonid and Jim Schultz of Dirt Cheap Diamonds conducted a survey in NY with a similar stone found the same correlation as well. The observers in each survey selected the GIA Ex steep/deep as a diamond with favorable optical properties and was never in the minority. It should be pointed out that these surveys were not exhaustive nor conclusive and were not controlled to the extent that many would like to see, however that does not mean the correlating data should be ignored either. Sergey Sivolenko of Moscow State University also stated that with certain diamonds that exhibit leakage under the table similar in proportions to these diamonds, that they do not have leakage visible to human beings using stereo vision. This is a very important note to point out. The question that begs an answer then is at what degree can human vision not detect leakage under the table? We are still researching the answer to this question. GIA’s observation testing indicates proportion combinations up to 36 degree crown angles coupled with 41.4 pavilion angles, a table in the mid 50’s and a depth around 63%. See graphic below.

In Section 3 of Garry’s article he features photography of the GIA Ex steep/deep against various backgrounds already introduced. Again it is our professional opinion that the bright white background gives the stone the brightest appearance between the white and gray backgrounds however we personally feel the picture taken against the black background actually makes it appear the brightest. We believe this is due to overexposure with the camera settings since a professional SLR was not used in the photography to our knowledge.

The image of the same diamond resting against Garry’s finger we feel shows a mixed balance between images 1 (on the white tray) and 2 against the neutral gray tray as you can easily see both lighter & darker results of the diamond on Garry’s hand. This may be due to the tilt of the stone on Garry’s hand as one can plainly see the lighter areas (pointed to in blue by myself) and the darker areas (pointed to in green by me).

Figure 4. Close ups of the GIA deep “Excellent Cut” (stone C from Table 1): 1.- on a white tray; 2.- on GIA’s gray tray. 3.- on black background. 4. & 5.- Ideal-Scope and AGS ASET photos. 6.- on fingers

Another interesting note about the above photography by Garry is that the leakage seen in photo #3 against the black background, in normal viewing circumstances with stereo vision (2 eyes) we believe this is not detectable.

Had the diamond been photographed in the face up view we believe you’d actually see more of the lighter areas of this particular GIA Ex steep/deep. At the time of this publishing we do not have a GIA Ex steep/deep on hand but we do have a steep/deep GIA Good (not excellent) to demonstrate this with.

The photograph below, taken with an SLR camera is of a GIA Good steep/deep and in this picture you can see the lighter areas under the table as well as my skin through the bottom of the stone.

I am not attempting prove that excessive leakage is a good thing by this example so please do not misinterpret what I’m saying about the particular “good” stone in this example. When we make the same comparison next to a GIA Ex in the same lighting, backdrop and camera the higher brightness (and contrast) of the GIA Ex can plainly be seen in the example below.

These same optical differences and characteristics can be observed in GIA’s DiamondDock lighting as well distinguishing the differences in the brighter diamond on the left.

So whether using the neutral background of the flesh or the neutral backdrop of the gray tray provided with GIA’s DiamondDock lighting the observations and conclusions are the same. We compare even more views in the accompanying video program and there is no skewing of viewer preferences as suggested in Garry’s article.

Not long ago we had a GIA Ex steep/deep in our possession and here is a photograph we took of it alongside the same GIA “Good” steep deep” for a comparison.

As you can see from the above photograph the GIA Ex steep/deep on the left has entirely different optical properties (greater brightness) than the GIA Good steep/deep on the right. This comparison can be drawn no matter which viewing environment you bring the diamonds into. It is our conviction that one of the major flaws of the HCA is that it lumps these 2 diamonds into the same category (steep/deep). Garry has become aware of these issues and has expressed the need to revise the HCA. We applaud his open-mindedness to these issues of course.

Section 4 Garry’s article presents some observation testing with the sample stones in his article. Interestingly the results correlate with both the GIA and AGS grades.

4. Preferences of observers of different ages

Figure 5 shows observers under 30 years of age (top and center) examining the three diamonds resting in their fingers. On the lower row an older observer is examining the stones. On the center right is a dome used by the GIA to replicate the Diamond Dock® ‘brightness’ lighting.

While white domes were used in GIA’s initial testing, they were not used in their actual observation testing. It is not meant to replicate brightness to any certain degree of accuracy.

Younger observers preferred the ‘ideal’ (B) followed by the deep stone (C). Older observers preferred the shallow (A), followed by the ‘ideal’ stone (B). The dome in Figure 5 was used by the GIA and has a central peep hole and a dark area that mimics 46° obstruction of the available 180° of illumination.

Figure 5. Observers of different ages (young, top and center and older, lower) examining the three diamonds resting in their fingers. On the center right is a dome used by the GIA to replicate the Diamond Dock® ‘brightness’ lighting.

While the issue of the dome is not worth talking further about, there is something very interesting to note about the above observers and how they arrived at their conclusions. Look carefully at the distance with which the observers are examining the diamonds. When a person looks at a diamond each person views them at various and different focal lengths. I.e. The distance from the eyes of the observer to the subject diamond in question. Note that the younger observers in Garry’s experiment are holding the diamonds considerably closer to their eyes than the older observer. Garry’s photography of these individuals making their observations suggest that they have a shorter focal length than the older person does and this is generally due to the nature of human vision diminishing as we all get older or with folks who have a tougher time focusing at shorter distances. At 42 years old my own personal focal length is around the 12 inch zone and I am slightly near sighted, meaning I can focus on things fine and sharp up close but need a mild prescription to look at things at a distance. The older observer is also wearing glasses to examine the diamond which indicates she may be far-sighted (i.e. needing glasses to focus at objects up close) and even at that her focal length is still greater than the younger observers.

The point is this … shallow diamonds take on a darker appearance as focal length decreases due to greater head/body obstruction. So people who have focal lengths that are greater will not see the darkness/obstruction as much as folks do who have shorter focal lengths. While Garry’s extremely limited observation test (of 3 people) is certainly not enough to draw any concrete conclusions from, it is worthy to note that the majority opinions were for stone #2 first (the stone closest to Tolkowsky ideal). Second the GIA Ex steep/deep and lastly the shallow stone by the older observer or … GIA Ex, GIA Ex then GIA Very Good. If anything this makes a case for GIA’s system, not against it.

In Garry’s experiment with these 3 people we also do not know the questions asked of them and the older observer may indeed have just picked that diamond for the spread factor alone, perhaps willing to sacrifice optics for size (totally understandable based on personal preferences).

Chapter 5 discusses the spread factors of the stones in Garry’s experiment. We are in agreement here. Shallower diamonds are spreadier.

In the next section Garry examines how AGS would grade the stones.

Discussion

1. How AGS would grade these diamonds?

The Lab Director of the American Gem Society diamond grading laboratory, Peter Yantzer, ran a Helium 3 Dimensional file through the AGS ASSET grading software and concluded that the deep stone (C) rates as AGS 2 and (A) rates AGS 3 on a scale where 0 is best and 10 is worst.

Stone (B) received 0 for light performance. It has an extra facet or natural on the pavilion that would lower the symmetry grade – probably to AGS 1.

Interestingly Garry’s observers chose the stones by preference in the order with which AGS graded the diamonds as well. Kudo’s to AGS. J It is also be interesting to note that the stones were also picked in GIA order as well with the shallower diamond taking the last preference and the Tolkowsky cut coming in first.

2. GIA Diamond Dock® Lighting

The left of Figure 7 shows a dealer using a typical fluorescent desk light with twin 15 watt fluorescent daylight tubes. The center photo shows stones being examined in a gray tray inside GIA’s Diamond Dock®. The third group of photo’s on the right are taken with the camera inside Diamond Dock®.

Figure 6 On the left is a typical dealer lighting[5], in the center stones are being examined in a gray tray in GIA’s Diamond Dock®. The third group of photographs clockwise from the top left – the camera is facing up from the position diamonds would be placed and the exposure is set on the lights – a 180° panorama taken into the room - and reflections seen in a spoon of a well lit diamond sorting room with a midday sun facing window.

The GIA Cut Study team appears to have replicated a diamond lighting environment used when buying and selling diamonds. Commercial diamond traders use a desk mounted twin fluorescent lamp, positioned so that light entering the pavilion makes inclusions easier to see when the diamond is held in tweezers and examined with a loupe; the more table leakage a diamond has in this lighting, the brighter the stone appears. Conversely many dealers do not like shallower diamonds; they appear relatively dark when backlit because they have less leakage because.

In actuality the GIA Cut Study team has taken the typical diamond lighting environments used when buying and selling diamonds and has removed the bright white background found in these environments to eliminate any confusion regarding the determination of brightness. As demonstrated in our video on the subject we show the differences in appearance between typical diamond dealer lighting (with bright background) and that same environment when using a neutral colored background (i.e. the gray tray used for DiamondDock viewing). Far from replicating a deceptive viewing environment GIA has taken steps to give the grader the proper tools and suggestions necessary to properly assess brightness even if they choose not to use the DiamondDock.

Lighting brightness is a squared function of distance; if GIA’s twin fluorescent light was mounted in an office or home ceiling, the brightness would be between 30 and 100 times dimmer (depending on the distance to the diamond) than the light in Diamond Dock, which is 33cm (13 inches) or less from the diamonds being graded. The overall brightness of the illuminated area inside the light box alters the way we perceive brightness and contrast.

In the video content we shot on brightness we have found that the DiamondDock does not alter the way we perceive brightness. The conclusions made by ourselves and our observers are all in accord. The DiamondDock does not show any conflicting results with what we observe in any other environment depicting brightness. We believe it is so clear in fact that any layman viewing the video can visually see the differences we were determining in the live analysis for themselves.

Contrary to common belief, a diamond viewed in more intense light on a light colored background appears darker because our eyes physiological response is to reduce the size of our pupil. The same auto exposure function resulted in the white tray (top) in Figure 2 having a gray appearance in the photo. This means that differences between diamonds return is minimized compared to the difference we would see in normal lighting. This is also a partial explanation of why the difference between the three diamonds is more apparent on the black tray.

A second contributing factor is the leakage in stone (C) that illuminates part of the tray behind the stone. This illuminates the tray making the leakage area brighter than it would otherwise be in all but the black tray (Figure 4).

Interestingly we do not see this in Garry’s photography. In fact we see that the gray tray does not make the diamond appear as bright when compared against the white backdrop. Remember this comparison.

Unless a diamond is cut with proportions that gather light from the direction of the lights in Diamond Dock®, it would not be favored. If a seat was set at a fixed height, then short people would favor deeper diamonds; a Tolkowsky ‘ideal’ diamond would gather very little light from the light box as much of its potential illumination would come from the area of relative darkness outside the light box and behind the observer (see Figure 8). Very tall people however would favor shallow stones; these return more light from higher angles or from a more face up direction.

Figure 8 shows DiamCalc ray paths for progressively deeper diamonds: 40.5°, 41.0° and 41.5° pavilion angles and crown angles of 33°, 34° and 35° respectively. Note the angle of the light entering (or leaving) the crown facet.

We do not disagree with Garry regarding what observers may prefer however the differences in preference are not due to DiamondDock lighting as Garry is implying but with the focal lengths of the individual observers. Light in the DiamondDock is not being channeled through a specific and limited narrow space. It is evenly diffused and dispersed over the crown of the diamond as the diamond is rocked and tilted back and forth so the observer is viewing a balanced and even display of cool, diffuse day lighting over the entirety of the stone. Any apparent darkness is not caused by the DD itself but by

3. Comparison with Master CZ’s

A number of photographs in Figure 9 of the same two Cubic Zirconia stones have been taken in various types of typical lighting. The photo on the gray tray (fourth from the top) is taken inside Diamond Dock®.

Figure 7 Several photographs of the same good (left) and bad (right) Cubic Zirconia stones (used for Ideal-scope demonstrations) were taken in various lightings. The photo on the gray tray is taken inside Diamond Dock®

The stone on the left is a very well cut CZ used as a calibration stone with an Ideal-scope. The stone on the right is an extremely steep / deep stone that is used to demonstrate how poor a bad cut can be. When viewed in the Diamond Dock® the relative difference between these two stones was minimal. There was perhaps the least difference between the beauty of the CZ’s that I have witnessed; I always carry these two stones with me in a small viewing box as a tool for analysis of the effects of various types of lighting.

While we cannot comment on the quality of the cubic zirconia’s that Garry used or the photographic equipment, here is a photograph we have taken under the DiamondDock of a Signity Star CZ (H&A quality) alongside a common steep/deep diamond (Good). We do not see the DiamondDock showing this good cz as being bad nor the bad diamond as being good. It appears brighter to us and we believe this photograph captures the difference in brightness between the 2 stones quite nicely too.

Update 8/22/06:
Heated debates have ran on about this very subject and right before the summer a fellow tradesmen of mine whom I respect made the following statement which lead to our acquirement of the test cz's Garry used in this very article.
(to be continued...)

Garry's Conclusion and Solution

Conclusion:

It would appear that GIA have replicated dealers lighting, at very close proximity, which favours diamonds with steeper crown angles and deeper pavilions. The use of a gray tray further contributes to deeper stone preferences. It appears that computer metrics for brightness and fire have little or no role to play, and GIA have no metric or measure for scintillation.

What should you do?

The good news: GIA now provides proportion information. The author suggests using my own development, the Holloway Cut Adviser (HCA) system to avoid diamonds with excessive leakage.

The bad news: GIA round the data heavily - if you get an HCA result near above 1.5, and you have not seen the diamond then you could request an ideal-scope photo.

Ideal-scope images (also my product) are a good way to asses any round diamonds performance, and they are easy to interpret and give a better indication a diamonds performance than HCA.

It is evidenced by the lack of research that went into this article that the conclusions drawn are faulty. It appears the article was written in haste plus a lack of tools, and the time necessary to properly test and observe the stones in question are also evident to this researcher. I personally know Garry for many years and I do not, for one moment doubt his sincerity or his intentions to serve the public with good and proper information but at just about every turn we are finding the results of his conclusions to disagree with the simple observations we are making on a daily basis which can be demonstrated both with professional photography and videography.

Contrary to his statement “It would appear that GIA have replicated dealers lighting, at very close proximity, which favours diamonds with steeper crown angles and deeper pavilions.” We have shown and demonstrated in our photography & video on “The Assessment of Brightness” that the DiamondDock lighting does not replicate dealer lighting. We demonstrate the slightly deceptive nature of dealer lighting and how it could lead one to draw faulty conclusions about the observance of brightness and how the addition of a neutral gray background (instead of the bright white backgrounds often found in dealers lighting) help in the assessment of brightness although we personally feel the DiamondDock lighting does an even better job than the typical desktop fluorescent lamp found in most dealers offices. Since Garry is likening the lighting to typical dealers lighting it is easy to understand where Garry is going wrong in his conclusions.

Regarding the statement “The use of a gray tray further contributes to deeper stone preferences.” We would like to point out that it certainly does not as evidenced by the last photograph of that vs the good cz as well as the photograph of the GIA Ex steep/deep alongside the bad steep/deep.

Here is the bottom line with what is currently being categorized as “steep/deeps” and the problem with Garry’s conclusions and assessment. Up until very recent times Garry as well as myself and others who have been in the vacuum of examining diamonds through reflector technologies categorized all diamonds with leakage under the table as “steep/deeps”. This author (myself) is the one who coined the term “ring of death” and the ever so faint presence of it meant elimination from our buying procedures. Our current inventory of our most popular rounds reflects this thinking. This leakage generally occurs once pavilion angles start hitting the 41 degree range and at the current time (if Garry hasn’t changed it yet) any stone having a pavilion angle at or even slightly over 41 degrees takes a BIG HIT in the HCA score.

Our studies into the GIA Cut Grading system and communications with the Cut Study Team have forced us to take a hard look at diamonds we once would not even consider. We currently haven’t made any hard core decisions about purchasing for inventory or not but we have had to take a step out of our shoes so to speak to see if GIA was out of their minds or not, suggesting what we have always considered certain steep/deep combinations as being “bright” and “fiery” stones. Admittedly I chuckled at the notion and was extremely skeptical until I received our first GIA Ex steep/deep which I was able to use in an observational survey we conducted next to a GIA VG (current AGS ideal) with painted girdle facets. Out of 30 observers we showed the comparison to 26.5 (we allowed them to pick a preference for brightness and fire) picked the GIA Ex steep/deep!!! That study caused me to rethink the whole steep/deep issue. Sergey of MSU came out and told me in a recent posting, THAT IS A FINE DIAMOND!?!? Where has Sergey been all this time on this issue? These truths I know have also penetrated the mind of Garry who is now also rethinking the HCA system. Both Garry and I (both research gemologists) are now realizing that it is wrong to lump all the stones we were considering steep/deep into one category. Particularly the 2 stones I had used in the demonstration earlier, shown again below.

To label both of these as crappers (steep/deep) is just plain wrong especially when majority opinion (about 90%) by consumers preferred the GIA Ex steep/deep on the left as more appealing to the eye in both brightness and fire than certain AGS Ideals (with girdle painting).

Addendum: Recently this graphic was posted on the forum suggesting problems with the DiamondDock attempting to demonstrate how DiamondDock lighting might also skew an environment accurate for assessing optical characteristics for brightness, fire and scintillation. The top graphic is meant to demonstrate true appearance and brightness of the stones in question while the bottom graphic is meant to demonstrate that when you bring diamonds too close to a light source how it can douse their appearance (apparently in the DiamondDock).

It is important to note that this picture was not taken in DiamondDock lighting but was the posters (Sergey) best attempt at trying to replicate it. Since we own the DiamondDock we took it upon ourselves to photograph a round brilliant cut diamond both at the bottom of the DiamondDock (proper viewing distance) and more towards the top and closer to the light source and use a white background similar to the graphic above to see if we can duplicate what Sergey was trying to demonstrate. Here is the photography of the same diamond both at the bottom of the viewing cabinet plus raised higher and closer to the light source.

We do not see any increase in darkness as depicted in Sergey’s graphic and it appears the same observation for brightness is and can be made. We would point out however that if you alter the lighting environment from diffuse daylight to spot lighting the body appearance of diamond does indeed take on a darker appearance as noted in the graphic below. This darker appearance however does not demonstrate any problem with DiamondDock lighting, but demonstrates natural phenomena seen when observing diamonds between diffuse daylight and spot lighting environments. This same comparison can be drawn if you were observing the diamonds in diffuse daylight (i.e. outside on a sunny day observing the diamond in the shade (brightness) then bringing the diamond into direct sunlight (fire)). We demonstrate this optical phenomenon in our video tutorial on the subject “The Assessment of Fire” showing both views and how the appearance of diamond is altered from one lighting environment to the next. We think Sergey may perhaps be confusing the appearance and the optical characteristics observed between the 2 different environments.

The bad news: GIA round the data heavily - if you get an HCA result near above 1.5, and you have not seen the diamond then you could request an ideal-scope photo.

Ideal-scope images (also my product) are a good way to asses any round diamonds performance, and they are easy to interpret and give a better indication a diamonds performance than HCA.