ASET Scope Theory

[Gnmu]

I was trying to explain to a friend the idea behind ASET images, but I found myself unable to justify the reasoning that red light is "better"/"intense" light, and that green light is "weaker" light. I'm going to put a disclaimer first that I am NOT trying to discredit anyone. I am just trying to learn. If you look online at some of the most reputable sources, you'll see something along the lines of:

AGS Site:
"Red represents light coming from angles where there is likely to be bright, direct sources of illumination in most viewing environments."

Whiteflash:
"...the most direct light entering a diamond will generally come from the higher angular ranges".

Brian Gavin Youtube:
Too long to quote. But the gist I got was the same as others, that most intense light was from above.

It seems to me that they've all assumed the viewing angle is roughly the same as the angle of the strongest light source (e.g. coming from behind my head). I agree this is the case if I'm looking down at a diamond with the table pointing towards the sun or lights above me, but what about real life situations. I want it to look fabulous with the diamond tilted in any direction, not just to me, but to other people! I could be holding onto a pole in the subway, with the lights above me, and my hand and diamond table facing the wall. I want that person beside me to think, damn, they've got a shiny rock!

But does the ASET image tell me anything about this scenario? The ASET scope is designed under the assumption that the strongest light source is 45-75 degrees relative to the diamond table plane when you look directly at the table. Can I infer what will happen if I'm still looking directly at the table, but the strongest light source is coming from 10 degrees relative to the table plane, with only weak ambient light from the 45-90 degree region?

 

[John P]

The up-front acknowledgment by AGS is that light can come from any direction, but our world is (primarily) lit from above. That's the basis. Stated on page 6.

https://cdn.ymaws.com/www.americangemsociety.org/resource/resmgr/images/AGSLab/ASETTheory-709.pdf

The HPD website page on ASET describes it as I would.

<< The AGS ASET Scope shows where in the hemisphere around you a diamond is gathering its light, and whether that light reflects back up to your eyes or “leaks” through the pavilion and is lost.

In a normal viewing position, around 25cm from your eyes, light from high above is color-coded blue in the ASET (your head often blocks this light). Light coming from around your shoulders is coded red (typically most desirable). Light from the sides is coded green. Light that is lost because it passes through the diamond creates a “window” where you can see what’s underneath the diamond (undesirable leakage). If the diamond has lighting behind it such leakage shows as white. If the diamond it sitting on a black platform it shows as black. >>

But does the ASET image tell me anything about this scenario? The ASET scope is designed under the assumption that the strongest light source is 45-75 degrees relative to the diamond table plane when you look directly at the table. Can I infer what will happen if I'm still looking directly at the table, but the strongest light source is coming from 10 degrees relative to the table plane, with only weak ambient light from the 45-90 degree region?

When I'm explaining ASET I stipulate it's a good way to see basic brightness and leakage, along with contrast elements, in a situation where the diamond is held still and primary lighting comes from above. But if you're sitting in a living room with lights on side tables but none above, the illumination scenario can favor a diamond that draws green.

Also: It's a completely static assessment. The next person who buys a brilliant cut diamond and only views it held perfectly still will be the first person to do that, I'd wager.

 

[Karl_K]

ASET is a static snapshot or approximation not a real world lighting environment.
The green/red thing and the broken obstruction model are some of the things wrong with it.
Diamond performance is dynamic not static is the bigget problem with it.
But it is arguably a good enough approximation to be useful.


The vast majority of living rooms in the US have more light in the green zone than red.

 

[Karl_K]

Consider this though everyone I have ever seen looking at their ring will move it to catch the light so the red green zone thing in the living room is not a huge issue.
The light paths are relative to the diamond so moving the diamond so the available light is in the red zone relative to the diamond is possible.
Further more many diamond cuts have secondary light paths that picks up light in the green zone even if the primary zone is red in ASET.

So it not cut and dried and works both ways.

 

[Texas Leaguer]

The structured ASET environment is used for more than the static face-up image. The AGS light performance grading system, of which ASET images are simply the graphical representation, assesses a 3D model of the diamond both face-up AND thru a range of tilt angles.

If a diamond is cut such that it will produce a good ASET image, that diamond will likely perform well in a wide range of lighting environments. If it has plenty of red and some green with limited amounts of leakage and a sufficient amount of structured contrast that is well distributed, it is likely optimized for all around performance.

 

[Gnmu]

The structured ASET environment is used for more than the static face-up image. The AGS light performance grading system, of which ASET images are simply the graphical representation, assesses a 3D model of the diamond both face-up AND thru a range of tilt angles.

If a diamond is cut such that it will produce a good ASET image, that diamond will likely perform well in a wide range of lighting environments. If it has plenty of red and some green with limited amounts of leakage and a sufficient amount of structured contrast that is well distributed, it is likely optimized for all around performance.

Thanks for the reply, and @Karl_K and @John Pollard! What you said is consistent with I'm beginning to understand. It seems that the static faceup ASET image is more of a proxy measurement, if you will. Presumably based on lots of research, a static faceup ASET with the ideal pattern implies with high confidence that the overall light performance will be optimal.

Are there public research papers (say AGS) demonstrating or validating this assertion, to quote "if it has plenty of red and some green with limited amounts of leakage and a sufficient amount of structured contrast that is well distributed, it is likely optimized for all around performance"? I'm curious why this is.

 

[Texas Leaguer]

Thanks for the reply, and @Karl_K and @John Pollard! What you said is consistent with I'm beginning to understand. It seems that the static faceup ASET image is more of a proxy measurement, if you will. Presumably based on lots of research, a static faceup ASET with the ideal pattern implies with high confidence that the overall light performance will be optimal.

Are there public research papers (say AGS) demonstrating or validating this assertion, to quote "if it has plenty of red and some green with limited amounts of leakage and a sufficient amount of structured contrast that is well distributed, it is likely optimized for all around performance"? I'm curious why this is.

Yes indeed. The AGSL light performance based cut grading system is a sophisticated, scientifically rigorous, and peer reviewed system. The overview article below will give you the basics. At the end of the article are links to the AGSL foundational articles in scientific publications.
https://www.whiteflash.com/about-diamonds/diamond-education/ags-cut-grading-scale.htm

 

[John P]

Are there public research papers (say AGS) demonstrating or validating this assertion, to quote "if it has plenty of red and some green with limited amounts of leakage and a sufficient amount of structured contrast that is well distributed, it is likely optimized for all around performance"? I'm curious why this is.

The foundation paper was published in 2007. Detailed on Pricescope back then by some handsome young fellow.
https://www.pricescope.com/communit...cognition-for-ags-cut-grade-technology.71945/

The agslab link in that post isn't working. And I see Google only knows that one.

Fortunately that same handsome fellow lectured on the Shanghai, Beijing and HK circuits for a few years about performance assessment, and he recalls Baidu replicating the SPIE content.
https://wenku.baidu.com/view/8896dcaddd3383c4bb4cd2f2.html

Maybe someone can retrieve and post a proper PDF. But the above gives you a basis.

 

[John P]

@Texas Leaguer - Did you happen to archive the SPIE journal article?

 

[Texas Leaguer]

@Texas Leaguer - Did you happen to archive the SPIE journal article?

Thanks for the heads up on the broken link JP. I will see if I can track it down.

 

[Texas Leaguer]

Attached is the spie article.
(the hyperlink in the article originally reference has been restored as well)

 

[bmfang]

@John Pollard & @Texas Leaguer : thanks for the links. Love geeking out with these articles.

 

[Garry H (Cut Nut)]

See my post in the pendants ASET thread.
People do a test.
Take a spoon or better still a shiny ice cream scoop and turn it upside down.
You can see where lights are coming from reflected in the shiny convex shape. Windows in daytime are far brighter than most lights. Great for pendants. Brilliance is more important there than fire.
You can also check the color temp of lights. Halogen look Orange yellow. Less can look warm or very blue cold. Daylight is usually pure white unless the sky is very blue.

 

[Gnmu]

See my post in the pendants ASET thread.
People do a test.
Take a spoon or better still a shiny ice cream scoop and turn it upside down.
You can see where lights are coming from reflected in the shiny convex shape. Windows in daytime are far brighter than most lights. Great for pendants. Brilliance is more important there than fire.
You can also check the color temp of lights. Halogen look Orange yellow. Less can look warm or very blue cold. Daylight is usually pure white unless the sky is very blue.

Sorry @Garry H (Cut Nut) , I fear I don't quite understand which topic this is in response to. Using static face-up ASET imagery as an indicator of overall light performance?

 

[MikeBotha]

Just a thought on light intensity. Strong overhead light is a fair assumption to be the strongest source of light, like the light of the sun at midday. But we all have driven in conditions where we face the morning sun when we have to let the visors down so as not to be blinded by the sunlight, which is at a very, very low angle. The same scenario applies at night when a schmuck coming from the opposite direction drives on high beam - get the point? The fact is that the angular spectrum between 90 degrees and 180 degrees, represented by the green display in the ASET should not be seen as undesirable but rather as a bonus. It shows that the diamond is doing it's work by collecting light from the whole hemisphere and not just in the red zone. As long as there is a fair balance between the red and green and of course a little blue for contrast.
There is therefore nothing wrong with the ASET technology, but rather with the wrong interpretation of the ASET images. Something that lies close to my heart and that the industry is not really addressing is; where does the light go to once it leaves the diamond? I agree with Brian Gavin; how does a diamond look to the those around the wearer? Here the full hemisphere comes into play and not just the red zone.

 

[Karl_K]

Something that lies close to my heart and that the industry is not really addressing is; where does the light go to once it leaves the diamond? I agree with Brian Gavin; how does a diamond look to the those around the wearer?

Interesting question and welcome to PS in case I haven't welcomed you in the past.
I have what I call the 3 person theory.
3 people are standing side by side, one asks to see the center persons diamond and she puts her arm out for them to look.
The first person says wow that is fiery.
The center person says wow it is super bright white.
The 3rd person says nice while thinking it looks kinda dull.
They are all correct.
The are each seeing a different arrangement of virtual facets and each is seeing the diamond react to a different lighting environment all at the same time.

 

[kenny]

Here's how I understand the meaning of the 3 colors of a properly-taken ASET pic:
They tell us where the diamond's reflected light came from:

1. Green: near the horizon
2. Blue: Overhead
3. Red: In between

 

[Garry H (Cut Nut)]

Sorry @Garry H (Cut Nut) , I fear I don't quite understand which topic this is in response to. Using static face-up ASET imagery as an indicator of overall light performance?

The point is that you can imagine the diamond as an object that gathers it's light from where the bright and less bright but visible spots or parts of the spoon if the diamond was sitting in the same position.
During the day the light from a window (low angle likely and green in ASET) is usually the brightest by far, and very cold white. Lights in the ceiling or from lamps are rarely as bright and much warmer colors. A white refrigerator or stainless steel surface may show a dull reflection on the spoon.

These will be the available sources of sparkle in the diamond.

Then put your diamond in the same spot and move it a little and check when you can see that sparkle from each light source. You can shade individual sources with your hand to ID which sparkles come from where. Best to close one eye and sit very still but move and find which other facets light up.

If you open both eyes you most often see twice as many sparkles.

Do this and you will learn how diamonds work. If you know how diamonds work in quantified light sources you will understand how ASET works.