What do the different colors of an ASET mean? Why do I sometimes see red and green split in the center?

Todd, It is quite daunting and confusing, wading through all of the diamond information. Also, it seems quite inadequate to evaluate a diamond without actually seeing it. I have a few questions: (1) On the AGS light performance document, is it optimal to have the center of the diamond diagram color red? I notice that a lot have “green” at the center, while others have red. Does it make a difference? (2) Is it better to have the pavilion angle in the lower range? Can you please provide your expertise on the following diamonds we are considering? (details below) ~ Cindy S.

Hi Cindy, it can be daunting to wade through all of the diamond details, but thankfully it is something which I can do fairly quickly after spending more than 25+ years in the diamond business, so feel free to ask me to look over the details of any diamonds which you are considering.

ASET for Crafted by Infinity Diamond, AGS #104066143004All right if we take a look at the diamond quality document for the 1.172 carat, I-color, SI-1 clarity from High Performance Diamonds which you are considering, the round diamond shaped image located in the center of the diamond grading report represents the output from the Angular Spectrum Evaluation Tool (ASET) which is designed to determine how bright a diamond is and how it makes use of the light which is available to it within a hemisphere shaped room, which is designed to mimic the lighting earth’s atmosphere. The ASET image uses the colors red, green, and blue, to represent different levels of brightness and contrast; the tones black and white are used to represent light leakage.


What do the colors of an ASET mean?

As stated previously, the Angular Spectrum Evaluation Tool (ASET) was designed by the American Gem Society Laboratory (AGSL) to measure the degree of relative brightness being exhibited by a diamond, and to determine how the diamond is making use of the light which is available to it within a hemisphere shaped room which is intended to mimic the lighting atmosphere of the earth’s hemisphere.

The ASET uses the colors red, green, and blue to represent different intensities of brightness and contrast, it uses the tones black and white to indicate light leakage. Each color is used to represent a different range or angle of light as is available from that range of the earth’s hemisphere.

Specifically, the color red is used to represent light which strikes the diamond from perpendicular to the table facet, up to forty five degrees. This is the brightest range of light available to the diamond and these sections of the diamond will be more brilliant. If you’ve read my article on Tolkowsky’s Diamond Design, then you know that the term brilliant as used in this connotation, refers to the brightness of the diamond and not white sparkle, which is also referred to as brilliance.

The color green represents light which is not quite as bright, it strikes the diamond from 45° out to the edge of the horizon. While the areas colored green represent areas that are less bright, they are still bright, and the slight difference between the areas which are red and green, serve to increase the contrast within the diamond.  Contrast is the difference in shades of tone and color which enable our eyes to see depth, it is a critical factor of visual performance within a diamond.

What does a mixture of red and green mean in an ASET image?

ASET Scope, Angular Spectrum Evaluation Tool, AGS LaboratoryIt is completely normal for the center region of the table facet to be red or green in color, and quite often it is a combination of both colors, because they share the edge of the 45° spectrum, which separates the two colors.  If you look at the ASET scope pictured to the left, you will see that the two sections of red and green are connected, therefore any light which enters the diamond along the seam may appear either red, green, or a combination thereof. The color blue represents contrast which is what enables our eyes to see, this is light which could have entered the diamond, but which is being blocked by our heads (or a camera lens) as we observe the diamond.


Why is Contrast critical for visual performance?

Diamond Clarity Photograph, Brian Gavin Signature Diamond, AGS #104064813017The best way that I know how to demonstrate how contrast effects the visual performance of a diamond is to look at the arrows pattern which is visible within this 1.228 carat, G-color, SI-1 clarity, Signature Diamond from Brian Gavin. The arrows which appear black in this picture, are created by the dark lens of the camera reflecting off of the eight pavilion main facets which are located on the pavilion (lower half) of the diamond. These arrows appear blue in the ASET image because the top of the scope is blue. In the real world, the same effect which is called “head obstruction” is created by the shadow which your head creates when you look at the diamond.


The purpose of cutting diamonds to exhibit high amounts of contrast between the sections created by the separation of the lower girdle and pavilion main facets, is that it creates added depth in the appearance of the diamond. The visible difference between the dark and light sections of the diamond, make it appear more crisp and vibrant. Imagine the difference in the appearance of a tile floor which consists of all white tiles and one which is comprised of alternating black and white tiles, as you look across the floor, the black and white floor will exhibit more depth and be more vibrant, the same principle is true for diamonds.

In addition, diamonds which exhibit high levels of contrast, will appear to sparkle when viewed under fluorescent lighting, which lacks ultra violet, which is required to produce the flashes of brilliance and dispersion that is seen when diamonds are exposed to other types of lighting. So if you spend a lot of time under fluorescent lighting, such as in a traditional office environment, you definitely want to select a diamond designed to exhibit high levels of contrast, or the diamond is going to look dull and lifeless.

All right, let’s look at some diamonds:

Everything looks great about the 1.172 carat, I-color, SI-1 clarity from High Performance Diamonds and the 1.238 carat, I-color, SI-1 clarity from HPD. Both diamonds should be gorgeous and meet my expectations for overall cut quality, optical symmetry, inclusions, etc. Please tell Wink that I said hello if you reach out to him, we’ve been good friends for years and he should know that I’m talking about him!

So when you look at the ASET images for these two diamonds, the center of the table area for the 1.172 carat is all red, and it is all green for the 1.238 carat, and as discussed above, this is merely because both diamonds are reflecting light from the range of 45 degrees, which is shared by both the red and green indicators of the ASET scope.

Diamond Cutter Brian Gavin Shows Us How to Use an ASET ScopeThis picture of Brian Gavin using an ASET Scope shows how to use an ASET Scope and once again shows how the colored sections of the ASET are assembled. Because the red and green areas overlap at the forty five degree mark, the center region of the table facet on a diamond will frequently be either red, green, or a combination of both colors and either color is perfectly fine. ASET photographs of diamonds are taken using a special set-up which is available from the AGS Laboratory.


Everything looks good with the 1.228 carat, G-color, SI-1 clarity, Signature Diamond from Brian Gavin, likewise for the 1.271 carat, H-color, SI-1 from Brian Gavin. Both Brian Gavin and Paul Slegers (Crafted by Infinity) have very reliable production quality, I used to purchase diamonds directly from both of them and never returned their production for visual performance, it is one of the reasons why I’m able to recommend their diamonds so highly.  My decision to purchase a diamond from one over the other, would most likely be the result of one having exactly what I was looking for… When I’ve compared their diamonds side-by-side it has not been possible to make a decision as to which was better in terms of light return and sparkle factor.

Brian Gavin definitely does a better job of marketing himself and his diamonds, thus I feel he has a stronger presence and recognition in the market, but I don’t see a clear difference in terms of the overall quality and sparkle.

What is the Best Pavilion Angle for a Round Brilliant Cut Diamond?

Regarding pavilion angle, as long as it is between 40.6 – 40.9 degrees you’re in the “sweet spot” and there is not a discernible difference, provided that the crown angle is also within a comparable range, which I consider to be 34.3 – 34.9 degrees. Now the crown angle is 34.2 degrees on the 1.172 carat from Crafted by Infinity, but I’m willing to overlook that difference of one tenth of a degree, given that the pavilion angle is 40.9 degrees and everything else about the diamond looks phenomenal… but for the record, my skin does begin to crawl at  34.0 degrees.

Todd Gray
Todd Gray is a professional diamond buyer with 30+ years of trade experience. He loves to teach people how to buy diamonds that exhibit incredible light performance! In addition to writing for Nice Ice, Todd "ghost writes" blogs and educational content for other diamond sites. When Todd isn't chained to a desk, or consulting for the trade, he enjoys Freediving! (that's like scuba diving, but without air tanks)
Todd Gray


Professional diamond buyer with 30+ years trade experience in the niche of super ideal cut diamonds. In my free time, I enjoy freediving & photography.
The incredible #story behind the Sirisha diamond necklace by @BrianGavin 71 #Diamonds cut to order #Amazinghttps://t.co/dHOo1T99xT - 3 years ago

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