Experts needed on Diamond Proportions.

[John P]

GIA do not have a cut grading system, they have the equivalent of HCA as a rejection system, but they made a mess of their model too because of the limitations of their light box used with a flawed sample of 'popular observers' i.e. dealers. But GIA's system can never ever be rolled out for anything other than round cuts. so it is a rejection system, not anything like a beauty or performance system

Adding to this for casual readers: Obstruction is why the HCA and GIA disagree so much.

The HCA likes shallow combos. But GIA's obstruction model causes dark patterns in many shallow combos, and the system is much more permissive at the deep side. Thus, some GIA EX = HCA FAIR and some HCA EX = GIA GOOD.

Example: Pavilion angle ranges for 61D 56T 34.5CA.
GIA EX = 40.6 - 41.6
HCA EX = 39.7 - 41.0

That's a significant disagreement.

Mass manufacturers will always cut deep to retain more weight from the average rough. That's why HCA-rejected combos exist in abundance. It's a simple numbers game. For big operations, cutting to the deep side of GIA EX is the most profitable plan.

Bryan I agree with Karl, on both obstruction and binocular vision. Interesting though is that Peter Yantzer explained to me that the leakage patch in the center of many princess cuts disappears with close up stereo vision. One eye sees a bright area and the other eye sees a bright area in the opposing sides - check it. But from further away many stones still show the leakage, so their overly close model does not work always!

I'm with Karl too. He likes 3 distances. Coincidentally, that's how I train ppl to make comparisons.

AGSL uses 2 at the lab; half-arm and close (30-40deg). Both closer than Garry may like.

I thought I'd add AGSL cut-charts here.

Example: Pavilion angle ranges for 61D 56T 34.5CA.
GIA EX = 40.6 - 41.6
HCA EX = 39.7 - 41.0
AGSL 0 = 40.5 - 41.1

The AGSL cut-charts fall in the middle, omitting shallowest from HCA and deepest from GIA.

*Important disclaimer* That range is only cut-chart data. Unlike the others, AGSL tests every diamond individually. It's therefore possible for some combos outside the above to earn 0, and some inside the above to be penalized. It depends on how all 57 facets work together in specific testing.

 

[Karl_K]

I'm with Karl too. He likes 3 distances. Coincidentally, that's how I train ppl to make comparisons.

AGSL uses 2 at the lab; half-arm and close (30-40deg). Both closer than Garry may like.

gmta lol
AGS uses close and unnatural.
25cm or 9.84 inches
Part of the problem is shown here:
http://www.agslab.com/members/content/docs/Complete_Explanation_of_AGS_Cut_System.pdf
Look at how they have people looking at diamonds on page 16 and 17.
If you did a real world study of how people looked at diamonds in the real world you would see the problem right away.
The other part of the problem is they assume diamonds only return light to the eyes from the side the viewer is on. While one side may have high obstruction the other has little.
In the real world it is asymmetrical obstruction not symmetrical and their own images show it.

 

[Garry H (Cut Nut)]

Gents please factor in that as round diamonds get shallower they get bigger in spread or diameter. So 20% of the weighting in HCA is for spread, so infact the optics can take a small hit for the shallowest stones because of the weighting to spread.

PS i am yet to have anyone argue that spread should not be an important factor for anyone buying a diamond. However none of the discussed labs gives it any credence (other than dinging really lousy spread diamonds).

 

[Texas Leaguer]

Gents please factor in that as round diamonds get shallower they get bigger in spread or diameter. So 20% of the weighting in HCA is for spread, so infact the optics can take a small hit for the shallowest stones because of the weighting to spread.

PS i am yet to have anyone argue that spread should not be an important factor for anyone buying a diamond. However none of the discussed labs gives it any credence (other than dinging really lousy spread diamonds).

Clearly spread is an important factor. How much weight it is given and how much performance loss it should be allowed to compensate for is part of the "art" of designing an evaluation system. In general I think I fall on the side of penalizing for it rather than rewarding for it. It is the type of factor that should have a default range in my mind - variances over or below that range would indicate deficits of one sort or another.

 

[John P]

Let's remember that GIA's obstruction metric is why this thread was started. The diamond in post#1 has a 40.4 PA and GIA rejects anything <40.6 from EX... Meanwhile HCA gives it EX, it's a candidate for AGS 0 and I've seen plenty of 40.4 with complimentary angles that are extremely beautiful.

Differences in approach, including distance-theory, are why I always advocate to treat every diamond separately.

Obstruction assessment is the main area of departure in assessment of brightness/pattern between (ascending order, I believe) HCA, AGA, AGSL, IGI, GIA & HRD.

RE Spread: I'd vote to reward diamonds cut to return light from edge to edge in all lighting conditions. For many cutting choices which cause the edges to go dark away from showroom spotlights I'd throw the penalty flag.

 

[Texas Leaguer]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

 

[Karl_K]

And we recognize that to have scintillation a diamond must have positive contrast.

While obstruction and leakage can and do provide contrast they are not the only source of scintillation. The environment is a big factor that reflectors do not take into account.
With no head shadow moving a diamond under an all white cone there would be little scintillation but under a cone modeled on the real world there would be. Now add some head shadow(dark disk to both) and there would be more scintillation in both but the real world modeled one would still have more.
Why?
Remember those ETAS images I posted a while back that show how dispersed the light draw that hits the eye from a diamond is around it? (this image is tilted to show the range the round grouping in the top third is above the table.)

 

[Garry H (Cut Nut)]

The GIA obstruction zone is all the light that does not come from outside their dumb light box which was used in a darkened room.
They called it DiamondDock, and it now is used as a color grading box.
this shows a 2D observer obstruction - but to the sides the entire very large environment was black, or very dark as the room was darkened.
it was part of a discussion a long time ago on this forum. It includes some AGS data.
You can see there is way too much blue, so of course shallow stones were dinged.
really badly flawed lighting, nothing like a jewellery store, but very like the environ's used by dealers, hence it got David's support. Hopefully David you learned more since then. They still use a very similar light box for fancy colour face up grading and it gives equally silly resluts for well cut rounds - they look dark and often get Fancy Deep or Fancy Dark when they actually face up much better in RL.

 

[Garry H (Cut Nut)]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Bryan the difinitive work to answer your question is the Cut group article published in 3 versions last year.
It is a heavy read, but unless you come to understand it you will never really understand the issues for obstruction, brilliance and scintillation.
This article is possibly 3 years ahead of comprehension.
http://www.gem.org.au/ckfinder/userfiles/files/GAA_Journal_V25_No3_web2(1).pdf
Pages 93 to 100 cover the topic at hand and, together with Bruce Hardings findings from 30 years earlier, you can see the fundamental flaws in AGS's one eyed view.
If you read it and understand the unreal effects of stereo vision you will be happy, I promise

 

[Rockdiamond]

The GIA obstruction zone is all the light that does not come from outside their dumb light box which was used in a darkened room.
They called it DiamondDock, and it now is used as a color grading box.
this shows a 2D observer obstruction - but to the sides the entire very large environment was black, or very dark as the room was darkened.
it was part of a discussion a long time ago on this forum. It includes some AGS data.
You can see there is way too much blue, so of course shallow stones were dinged.
really badly flawed lighting, nothing like a jewellery store, but very like the environ's used by dealers, hence it got David's support. Hopefully David you learned more since then. They still use a very similar light box for fancy colour face up grading and it gives equally silly resluts for well cut rounds - they look dark and often get Fancy Deep or Fancy Dark when they actually face up much better in RL.

Hi Garry!
I do believe you're mistaken about my support of the DiamondDock....it has been a lot of years so I can't swear it...
But I can say that we agree completely today!
The DD is a very single minded method- ignoring many physical realities of a diamond's grade, and real life viewing.

If you think about it, any of the standardization which has been adapted for color grading leads to some individual stones getting the wrong grade in real life.
Starting with colorless stones being graded through the pavilion.

 

[Texas Leaguer]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Bryan the difinitive work to answer your question is the Cut group article published in 3 versions last year.
It is a heavy read, but unless you come to understand it you will never really understand the issues for obstruction, brilliance and scintillation.
This article is possibly 3 years ahead of comprehension.
http://www.gem.org.au/ckfinder/userfiles/files/GAA_Journal_V25_No3_web2(1).pdf
Pages 93 to 100 cover the topic at hand and, together with Bruce Hardings findings from 30 years earlier, you can see the fundamental flaws in AGS's one eyed view.
If you read it and understand the unreal effects of stereo vision you will be happy, I promise

Thanks Garry,
I have looked at this work before although I can't say I have really made a study of it. I will make it a point to do that soon. I have been very intrigued with the pieces you have posted from that work relating to how the brain processes visual information.

I was hoping to get a sense of how much actionable information can be extrapolated from the amount of obstruction we see in static ASET images. That is, can a given ASET and the amount and distribution of blue we see enable us to make valid conclusions about how the diamond will perform in the real world to observers with stereoscopic vision? Or, are static ASET images somehow misleading in terms of the amount of blue we see and how that translates to all around performance. In other words, although more sophisticated evaluation is possible, will the insights gained diverge significantly from the insights the simple version of the test reveals?

 

[Garry H (Cut Nut)]

The GIA obstruction zone is all the light that does not come from outside their dumb light box which was used in a darkened room.
They called it DiamondDock, and it now is used as a color grading box.
this shows a 2D observer obstruction - but to the sides the entire very large environment was black, or very dark as the room was darkened.
it was part of a discussion a long time ago on this forum. It includes some AGS data.
You can see there is way too much blue, so of course shallow stones were dinged.
really badly flawed lighting, nothing like a jewellery store, but very like the environ's used by dealers, hence it got David's support. Hopefully David you learned more since then. They still use a very similar light box for fancy colour face up grading and it gives equally silly resluts for well cut rounds - they look dark and often get Fancy Deep or Fancy Dark when they actually face up much better in RL.

Hi Garry!
I do believe you're mistaken about my support of the DiamondDock....it has been a lot of years so I can't swear it...
But I can say that we agree completely today!
The DD is a very single minded method- ignoring many physical realities of a diamond's grade, and real life viewing.

If you think about it, any of the standardization which has been adapted for color grading leads to some individual stones getting the wrong grade in real life.
Starting with colorless stones being graded through the pavilion.

Good to hear David.
And yes, grading diamonds thru the pavilion is nuts, and if some smart lawyers wanted to set up a class action for misrepresentation of products, then its possibly a +100 billion payout.

 

[Garry H (Cut Nut)]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Bryan the difinitive work to answer your question is the Cut group article published in 3 versions last year.
It is a heavy read, but unless you come to understand it you will never really understand the issues for obstruction, brilliance and scintillation.
This article is possibly 3 years ahead of comprehension.
http://www.gem.org.au/ckfinder/userfiles/files/GAA_Journal_V25_No3_web2(1).pdf
Pages 93 to 100 cover the topic at hand and, together with Bruce Hardings findings from 30 years earlier, you can see the fundamental flaws in AGS's one eyed view.
If you read it and understand the unreal effects of stereo vision you will be happy, I promise

Thanks Garry,
I have looked at this work before although I can't say I have really made a study of it. I will make it a point to do that soon. I have been very intrigued with the pieces you have posted from that work relating to how the brain processes visual information.

I was hoping to get a sense of how much actionable information can be extrapolated from the amount of obstruction we see in static ASET images. That is, can a given ASET and the amount and distribution of blue we see enable us to make valid conclusions about how the diamond will perform in the real world to observers with stereoscopic vision? Or, are static ASET images somehow misleading in terms of the amount of blue we see and how that translates to all around performance. In other words, although more sophisticated evaluation is possible, will the insights gained diverge significantly from the insights the simple version of the test reveals?

the easiest way to explain will be to send you a DiamCalc file of an emerald cut that when tilted has strong blue bands that turn red on alternate sides. Face up the stone is almost totally blue. But when you look at the stone it has real life. Its a simple test. So I never look at a straight up ASET for non rounds, I always tilt to about 8 degrees left and 8 to the right. Then if the stone passes that test, I tilt to me and away.

 

[Texas Leaguer]

The GIA obstruction zone is all the light that does not come from outside their dumb light box which was used in a darkened room.
They called it DiamondDock, and it now is used as a color grading box.
this shows a 2D observer obstruction - but to the sides the entire very large environment was black, or very dark as the room was darkened.
it was part of a discussion a long time ago on this forum. It includes some AGS data.
You can see there is way too much blue, so of course shallow stones were dinged.
really badly flawed lighting, nothing like a jewellery store, but very like the environ's used by dealers, hence it got David's support. Hopefully David you learned more since then. They still use a very similar light box for fancy colour face up grading and it gives equally silly resluts for well cut rounds - they look dark and often get Fancy Deep or Fancy Dark when they actually face up much better in RL.

Hi Garry!
I do believe you're mistaken about my support of the DiamondDock....it has been a lot of years so I can't swear it...
But I can say that we agree completely today!
The DD is a very single minded method- ignoring many physical realities of a diamond's grade, and real life viewing.

If you think about it, any of the standardization which has been adapted for color grading leads to some individual stones getting the wrong grade in real life.
Starting with colorless stones being graded through the pavilion.

Good to hear David.
And yes, grading diamonds thru the pavilion is nuts, and if some smart lawyers wanted to set up a class action for misrepresentation of products, then its possibly a +100 billion payout.

How should diamonds be color graded in order to assess true body color and not be influenced by cutting factors. Is it not best to keep those assessments independent of one another?

 

[Texas Leaguer]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Bryan the difinitive work to answer your question is the Cut group article published in 3 versions last year.
It is a heavy read, but unless you come to understand it you will never really understand the issues for obstruction, brilliance and scintillation.
This article is possibly 3 years ahead of comprehension.
http://www.gem.org.au/ckfinder/userfiles/files/GAA_Journal_V25_No3_web2(1).pdf
Pages 93 to 100 cover the topic at hand and, together with Bruce Hardings findings from 30 years earlier, you can see the fundamental flaws in AGS's one eyed view.
If you read it and understand the unreal effects of stereo vision you will be happy, I promise

Thanks Garry,
I have looked at this work before although I can't say I have really made a study of it. I will make it a point to do that soon. I have been very intrigued with the pieces you have posted from that work relating to how the brain processes visual information.

I was hoping to get a sense of how much actionable information can be extrapolated from the amount of obstruction we see in static ASET images. That is, can a given ASET and the amount and distribution of blue we see enable us to make valid conclusions about how the diamond will perform in the real world to observers with stereoscopic vision? Or, are static ASET images somehow misleading in terms of the amount of blue we see and how that translates to all around performance. In other words, although more sophisticated evaluation is possible, will the insights gained diverge significantly from the insights the simple version of the test reveals?

the easiest way to explain will be to send you a DiamCalc file of an emerald cut that when tilted has strong blue bands that turn red on alternate sides. Face up the stone is almost totally blue. But when you look at the stone it has real life. Its a simple test. So I never look at a straight up ASET for non rounds, I always tilt to about 8 degrees left and 8 to the right. Then if the stone passes that test, I tilt to me and away.

Yes, I think looking at tilt views is very helpful. After all, how often in real life is your line of site perfectly perpendicular to the table, compared to at a slight tilt angle?

Since step cuts have not been adopted by many in the trade for AGS analysis I am not sure that example would be as relevant to my general question. They may have flaws in the metric set up for one facet arrangement and not for others.

Since rounds, princess cuts and brilliant style cushions seem to be 90% of what AGS grades, do you think the obstruction model works well enough for those to give a strong indication of real world performance?

 

[Rockdiamond]

The GIA obstruction zone is all the light that does not come from outside their dumb light box which was used in a darkened room.
They called it DiamondDock, and it now is used as a color grading box.
this shows a 2D observer obstruction - but to the sides the entire very large environment was black, or very dark as the room was darkened.
it was part of a discussion a long time ago on this forum. It includes some AGS data.
You can see there is way too much blue, so of course shallow stones were dinged.
really badly flawed lighting, nothing like a jewellery store, but very like the environ's used by dealers, hence it got David's support. Hopefully David you learned more since then. They still use a very similar light box for fancy colour face up grading and it gives equally silly resluts for well cut rounds - they look dark and often get Fancy Deep or Fancy Dark when they actually face up much better in RL.

Hi Garry!
I do believe you're mistaken about my support of the DiamondDock....it has been a lot of years so I can't swear it...
But I can say that we agree completely today!
The DD is a very single minded method- ignoring many physical realities of a diamond's grade, and real life viewing.

If you think about it, any of the standardization which has been adapted for color grading leads to some individual stones getting the wrong grade in real life.
Starting with colorless stones being graded through the pavilion.

Good to hear David.
And yes, grading diamonds thru the pavilion is nuts, and if some smart lawyers wanted to set up a class action for misrepresentation of products, then its possibly a +100 billion payout.

How should diamonds be color graded in order to assess true body color and not be influenced by cutting factors. Is it not best to keep those assessments independent of one another?

In my opinion, it all goes back to common sense observation Bryan.
Take the diamond out of the diamond dock, turn it over and see how it faces up in normal viewing environments.
The factors involved are so very complex that trying to predict which changes based on cutting style misses the point IMO.
In other words- "better" cut does not necessarily make a stone face up whiter in all cases. Some, yes, all no.

Having said that, and knowing the research they've done, Garry and Serg are likely already working on something like this

 

[MelisendeDiamonds]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Bryan the difinitive work to answer your question is the Cut group article published in 3 versions last year.
It is a heavy read, but unless you come to understand it you will never really understand the issues for obstruction, brilliance and scintillation.
This article is possibly 3 years ahead of comprehension.
http://www.gem.org.au/ckfinder/userfiles/files/GAA_Journal_V25_No3_web2(1).pdf
Pages 93 to 100 cover the topic at hand and, together with Bruce Hardings findings from 30 years earlier, you can see the fundamental flaws in AGS's one eyed view.
If you read it and understand the unreal effects of stereo vision you will be happy, I promise

Gary it is so offputting to read constant promotion of the cut group and putting down of AGSL and GIAL on this board.
The labs aren't going to waste their time on this forum or any other so really these one sided monologues are so misleading.

Head size is a variable, viewing distance is a variable, spacing between the eyes is a variable(some races of people in general have eyes much closer together than others), as is diamond size. A powerful argument can and will be made that the effects of stereovision in a wide range of scenarios are insignificant and cyclops theory still remains perfectly valid and applicable.

So I'll pat you all on the back the 5 or 6 of you trademembers in this thread and your self important theories repeated over and over again. But really you all know or should know this thread and the dozen or so others you have created before or will create in the future have such little impact.

 

[Texas Leaguer]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Bryan the difinitive work to answer your question is the Cut group article published in 3 versions last year.
It is a heavy read, but unless you come to understand it you will never really understand the issues for obstruction, brilliance and scintillation.
This article is possibly 3 years ahead of comprehension.
http://www.gem.org.au/ckfinder/userfiles/files/GAA_Journal_V25_No3_web2(1).pdf
Pages 93 to 100 cover the topic at hand and, together with Bruce Hardings findings from 30 years earlier, you can see the fundamental flaws in AGS's one eyed view.
If you read it and understand the unreal effects of stereo vision you will be happy, I promise

Gary it is so offputting to read constant promotion of the cut group and putting down of AGSL and GIAL on this board.
The labs aren't going to waste their time on this forum or any other so really these one sided monologues are so misleading.

Head size is a variable, viewing distance is a variable, spacing between the eyes is a variable(some races of people in general have eyes much closer together than others), as is diamond size. A powerful argument can and will be made that the effects of stereovision in a wide range of scenarios are insignificant and cyclops theory still remains perfectly valid and applicable.

So I'll pat you all on the back the 5 or 6 of you trademembers in this thread and your self important theories repeated over and over again. But really you all know or should know this thread and the dozen or so others you have created before or will create in the future have such little impact.

Haroutioun,
That's a little harsh don't you think? Garry posted that link in response to a specific question, not in my opinion for self-promotional purposes. The fact that he has been involved in advanced research on the subject makes it interesting and potentially important information for other tradesmembers to be aware of.

The sense that people are criticizing the establishment goes with the territory of pushing the boundaries of current thought and practice. GIA and AGSL are not perfect and are both evolving, though not as fast as some would like in some areas. But they need to be challenged in order for progress to continue to occur.

Alot of what is discussed in the R&D circles never makes it to the mainstream. The fact that many ideas will probably have very little impact is not necessarily a reflection on the validity of those ideas. But you also might be surprised by the impact they are having. You may be looking at it from a rather narrow perspective.

 

[Texas Leaguer]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Head size is a variable, viewing distance is a variable, spacing between the eyes is a variable(some races of people in general have eyes much closer together than others), as is diamond size. A powerful argument can and will be made that the effects of stereovision in a wide range of scenarios are insignificant and cyclops theory still remains perfectly valid and applicable.

This is essentially the question I was digging at. I would like to hear the arguments pro and con. It is my understanding that when the AGS system was being developed, the stereo vision issue was recognized. However the computing power at the time for the extra ray tracing and analysis was not practical. It was determined that the cyclops model would be good enough to meet the purposes.

So I am curious how stereo analysis would change the LP grading standard. Would Ideal be easier to make because some of what we think is bad our brains are filtering out and making proper sense of?

I think most people agree that AGS0 are for the most part beautiful diamonds. So it can't be that far off in terms of rewarding great performance. One question then becomes, if stereovision analyis softened the standard, would that be a good thing? And overall, what would be the practical implications of such a change. If it does not change the basic validity of the system, would it be more of a tweak than a game changer?

 

[MelisendeDiamonds]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Head size is a variable, viewing distance is a variable, spacing between the eyes is a variable(some races of people in general have eyes much closer together than others), as is diamond size. A powerful argument can and will be made that the effects of stereovision in a wide range of scenarios are insignificant and cyclops theory still remains perfectly valid and applicable.

This is essentially the question I was digging at. I would like to hear the arguments pro and con. It is my understanding that when the AGS system was being developed, the stereo vision issue was recognized. However the computing power at the time for the extra ray tracing and analysis was not practical. It was determined that the cyclops model would be good enough to meet the purposes.

So I am curious how stereo analysis would change the LP grading standard. Would Ideal be easier to make because some of what we think is bad our brains are filtering out and making proper sense of?

I think most people agree that AGS0 are for the most part beautiful diamonds. So it can't be that far off in terms of rewarding great performance. One question then becomes, if stereovision analyis softened the standard, would that be a good thing? And overall, what would be the practical implications of such a change. If it does not change the basic validity of the system, would it be more of a tweak than a game changer?

Bryan,

This is also not the first time you have asked this question on this board or brought up this point.
https://www.pricescope.com/communit...real-life.203965/page-6#post-3718201#p3718201

Good-luck getting a more comprehensive answer this time.

 

[Garry H (Cut Nut)]

The GIA obstruction zone is all the light that does not come from outside their dumb light box which was used in a darkened room.
They called it DiamondDock, and it now is used as a color grading box.
this shows a 2D observer obstruction - but to the sides the entire very large environment was black, or very dark as the room was darkened.
it was part of a discussion a long time ago on this forum. It includes some AGS data.
You can see there is way too much blue, so of course shallow stones were dinged.
really badly flawed lighting, nothing like a jewellery store, but very like the environ's used by dealers, hence it got David's support. Hopefully David you learned more since then. They still use a very similar light box for fancy colour face up grading and it gives equally silly resluts for well cut rounds - they look dark and often get Fancy Deep or Fancy Dark when they actually face up much better in RL.

Hi Garry!
I do believe you're mistaken about my support of the DiamondDock....it has been a lot of years so I can't swear it...
But I can say that we agree completely today!
The DD is a very single minded method- ignoring many physical realities of a diamond's grade, and real life viewing.

If you think about it, any of the standardization which has been adapted for color grading leads to some individual stones getting the wrong grade in real life.
Starting with colorless stones being graded through the pavilion.

Good to hear David.
And yes, grading diamonds thru the pavilion is nuts, and if some smart lawyers wanted to set up a class action for misrepresentation of products, then its possibly a +100 billion payout.

How should diamonds be color graded in order to assess true body color and not be influenced by cutting factors. Is it not best to keep those assessments independent of one another?

Color is color. Why should consumers when buying diamonds not know what they are buying? How is the current color grading system assisting them? When a G colored diamond looks like a I and another G looks like a F?

 

[Garry H (Cut Nut)]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Bryan the difinitive work to answer your question is the Cut group article published in 3 versions last year.
It is a heavy read, but unless you come to understand it you will never really understand the issues for obstruction, brilliance and scintillation.
This article is possibly 3 years ahead of comprehension.
http://www.gem.org.au/ckfinder/userfiles/files/GAA_Journal_V25_No3_web2(1).pdf
Pages 93 to 100 cover the topic at hand and, together with Bruce Hardings findings from 30 years earlier, you can see the fundamental flaws in AGS's one eyed view.
If you read it and understand the unreal effects of stereo vision you will be happy, I promise

Thanks Garry,
I have looked at this work before although I can't say I have really made a study of it. I will make it a point to do that soon. I have been very intrigued with the pieces you have posted from that work relating to how the brain processes visual information.

I was hoping to get a sense of how much actionable information can be extrapolated from the amount of obstruction we see in static ASET images. That is, can a given ASET and the amount and distribution of blue we see enable us to make valid conclusions about how the diamond will perform in the real world to observers with stereoscopic vision? Or, are static ASET images somehow misleading in terms of the amount of blue we see and how that translates to all around performance. In other words, although more sophisticated evaluation is possible, will the insights gained diverge significantly from the insights the simple version of the test reveals?

the easiest way to explain will be to send you a DiamCalc file of an emerald cut that when tilted has strong blue bands that turn red on alternate sides. Face up the stone is almost totally blue. But when you look at the stone it has real life. Its a simple test. So I never look at a straight up ASET for non rounds, I always tilt to about 8 degrees left and 8 to the right. Then if the stone passes that test, I tilt to me and away.

Yes, I think looking at tilt views is very helpful. After all, how often in real life is your line of site perfectly perpendicular to the table, compared to at a slight tilt angle? Bryan it is impossible to have a front on view at 90 degrees unless you close one eye or get a very very long way away. That is point 1.

Since step cuts have not been adopted by many in the trade for AGS analysis I am not sure that example would be as relevant to my general question. They may have flaws in the metric set up for one facet arrangement and not for others.

Since rounds, princess cuts and brilliant style cushions seem to be 90% of what AGS grades, do you think the obstruction model works well enough for those to give a strong indication of real world performance? that is the point being discussed. The AGS monoscopic system has a flaw because humans have two eyes. And if they choose to grade from less than 10 inches (because that it a USA Army standard) then at that close distance the streoscopic factor is huge!

 

[Garry H (Cut Nut)]

The GIA obstruction zone is all the light that does not come from outside their dumb light box which was used in a darkened room.
They called it DiamondDock, and it now is used as a color grading box.
this shows a 2D observer obstruction - but to the sides the entire very large environment was black, or very dark as the room was darkened.
it was part of a discussion a long time ago on this forum. It includes some AGS data.
You can see there is way too much blue, so of course shallow stones were dinged.
really badly flawed lighting, nothing like a jewellery store, but very like the environ's used by dealers, hence it got David's support. Hopefully David you learned more since then. They still use a very similar light box for fancy colour face up grading and it gives equally silly resluts for well cut rounds - they look dark and often get Fancy Deep or Fancy Dark when they actually face up much better in RL.

Hi Garry!
I do believe you're mistaken about my support of the DiamondDock....it has been a lot of years so I can't swear it...
But I can say that we agree completely today!
The DD is a very single minded method- ignoring many physical realities of a diamond's grade, and real life viewing.

If you think about it, any of the standardization which has been adapted for color grading leads to some individual stones getting the wrong grade in real life.
Starting with colorless stones being graded through the pavilion.

Good to hear David.

And yes, grading diamonds thru the pavilion is nuts, and if some smart lawyers wanted to set up a class action for misrepresentation of products, then its possibly a +100 billion payout.

How should diamonds be color graded in order to assess true body color and not be influenced by cutting factors. Is it not best to keep those assessments independent of one another?

In my opinion, it all goes back to common sense observation Bryan.
Take the diamond out of the diamond dock, turn it over and see how it faces up in normal viewing environments.
The factors involved are so very complex that trying to predict which changes based on cutting style misses the point IMO.
In other words- "better" cut does not necessarily make a stone face up whiter in all cases. Some, yes, all no.

Having said that, and knowing the research they've done, Garry and Serg are likely already working on something like this

Not me, but the other 3 have a solution http://www.lexusindia.in/products/ap-oxygen-d2z.aspx

 

[Garry H (Cut Nut)]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Head size is a variable, viewing distance is a variable, spacing between the eyes is a variable(some races of people in general have eyes much closer together than others), as is diamond size. A powerful argument can and will be made that the effects of stereovision in a wide range of scenarios are insignificant and cyclops theory still remains perfectly valid and applicable.

This is essentially the question I was digging at. I would like to hear the arguments pro and con. It is my understanding that when the AGS system was being developed, the stereo vision issue was recognized. However the computing power at the time for the extra ray tracing and analysis was not practical. It was determined that the cyclops model would be good enough to meet the purposes.

So I am curious how stereo analysis would change the LP grading standard. Would Ideal be easier to make because some of what we think is bad our brains are filtering out and making proper sense of?

I think most people agree that AGS0 are for the most part beautiful diamonds. So it can't be that far off in terms of rewarding great performance. One question then becomes, if stereovision analyis softened the standard, would that be a good thing? And overall, what would be the practical implications of such a change. If it does not change the basic validity of the system, would it be more of a tweak than a game changer?

I don't think near enough is good enough.
HCA is near enough but it is not good enough, and if I were to add the minor facets, which is covered in my patent, then you have the GIA system.
If the system does not do emerald cuts, then there will be other individual stones that will either pass or fail that should fail or pass.
But my point here is not about AGS, its about obstruction modeling and if you want to make any system to 'look at' or 'evaluate' a diamond then you need a model or some rules.

Our very long article is about establishing rules, and identifying problems that need rules. What we have said is that where there are no rules possible (e.g. because of some unknown human vision / brain processes) then we could show people lots of diamonds in reproducable videos and let them compare stones side by side. And compare some of the actual diamond diamonds to their actual videos.
I am planning and training my staff to do this in my store.
in that situation, after building a large data base of peoples first choices (i.e. what sells fast) we should be able to fill in some of the gaps in human visual preferences.

If anyone or any org has a better way then please please share it. Happy to sign an NDA. Happy to invest.
But so far there are no diamond grading sytsems that grade the beauty and performance of diamonds.

 

[Garry H (Cut Nut)]

Bryan (and others) my hasp key that I forgot arrived. Here is the emerald cut that I mentioned. What one eye sees shows ASET blue obstruction on one side of the stone. Yet the other eye sees reasonable possible light return. In fact on close examination the stone looks very nice. I can not remember for sure what the AGS grade was but it was 5, 6 or 7.
Happy to emaiul the 3D file to anyone who can check it.

 

[Jambalaya]

Hi JohnPollard, you are absolutely correct. That's why this is an interesting topic for me and also a tough decision. The more I learn about diamonds, the more I'm appreciating the finer details, just like a great cabernet. The problem is, as a wine tasting novice, I wouldn't drop 18k on my first bottle. But I'm hoping i never have to propose again - although there's a 50% I might have to if the divorce rate continues its trend - so two buck chuck is out of the question.

BrownyJones - I have written a post to you in Hangout.

 

[Texas Leaguer]

Bryan (and others) my hasp key that I forgot arrived. Here is the emerald cut that I mentioned. What one eye sees shows ASET blue obstruction on one side of the stone. Yet the other eye sees reasonable possible light return. In fact on close examination the stone looks very nice. I can not remember for sure what the AGS grade was but it was 5, 6 or 7.
Happy to emaiul the 3D file to anyone who can check it.

That's a pretty telling example. Please do email me the file. Was the cut grade downgraded solely for excessive contrast?

Do you have any examples of outstanding rounds and princess that get significant downgrades in the AGS system for contrast which is not actually seen because of stereovision? And if so, does the stone still perform well at distance?

 

[Garry H (Cut Nut)]

Bryan (and others) my hasp key that I forgot arrived. Here is the emerald cut that I mentioned. What one eye sees shows ASET blue obstruction on one side of the stone. Yet the other eye sees reasonable possible light return. In fact on close examination the stone looks very nice. I can not remember for sure what the AGS grade was but it was 5, 6 or 7.
Happy to emaiul the 3D file to anyone who can check it.

That's a pretty telling example. Please do email me the file. Was the cut grade downgraded solely for excessive contrast?

Do you have any examples of outstanding rounds and princess that get significant downgrades in the AGS system for contrast which is not actually seen because of stereovision? And if so, does the stone still perform well at distance?

will send you the file Bryan. Of course there are many rounds that are shallowish that get dinged by AGS (and GIA) for whatever you want to call it. I doubt any princes cuts are downgraded as most have too little blue in ASET.

 

[Texas Leaguer]

Re: obscuration, can you all help me understand the relationship between head obscuration and positive contrast? We think about obscuration as something not desirable for close viewing- certainly when too much light is obscured by a head shadow of about 30 degrees. And we recognize that to have scintillation a diamond must have positive contrast. Isn't the amount and distribution of what we see as blue in ASET also a signature of contrast that we can extrapolate to a full range of viewing scenarios. In other words, is the static face-up view in ASET or ASET tilt views indicative of how we expect the diamond to react to light more or less across the board? (excluding the issue of stereo vision for the sake of this question)

Head size is a variable, viewing distance is a variable, spacing between the eyes is a variable(some races of people in general have eyes much closer together than others), as is diamond size. A powerful argument can and will be made that the effects of stereovision in a wide range of scenarios are insignificant and cyclops theory still remains perfectly valid and applicable.

This is essentially the question I was digging at. I would like to hear the arguments pro and con. It is my understanding that when the AGS system was being developed, the stereo vision issue was recognized. However the computing power at the time for the extra ray tracing and analysis was not practical. It was determined that the cyclops model would be good enough to meet the purposes.

So I am curious how stereo analysis would change the LP grading standard. Would Ideal be easier to make because some of what we think is bad our brains are filtering out and making proper sense of?

I think most people agree that AGS0 are for the most part beautiful diamonds. So it can't be that far off in terms of rewarding great performance. One question then becomes, if stereovision analyis softened the standard, would that be a good thing? And overall, what would be the practical implications of such a change. If it does not change the basic validity of the system, would it be more of a tweak than a game changer?

I don't think near enough is good enough.
HCA is near enough but it is not good enough, and if I were to add the minor facets, which is covered in my patent, then you have the GIA system.
If the system does not do emerald cuts, then there will be other individual stones that will either pass or fail that should fail or pass.
But my point here is not about AGS, its about obstruction modeling and if you want to make any system to 'look at' or 'evaluate' a diamond then you need a model or some rules.

Our very long article is about establishing rules, and identifying problems that need rules. What we have said is that where there are no rules possible (e.g. because of some unknown human vision / brain processes) then we could show people lots of diamonds in reproducable videos and let them compare stones side by side. And compare some of the actual diamond diamonds to their actual videos.
I am planning and training my staff to do this in my store.
in that situation, after building a large data base of peoples first choices (i.e. what sells fast) we should be able to fill in some of the gaps in human visual preferences.

If anyone or any org has a better way then please please share it. Happy to sign an NDA. Happy to invest.
But so far there are no diamond grading sytsems that grade the beauty and performance of diamonds.

Garry,
I have a question about this comment above:
"HCA is near enough but it is not good enough, and if I were to add the minor facets, which is covered in my patent, then you have the GIA system."
Why have you chosen not to add the minor facets? (Not that it would be a simple undertaking but you have available the advanced expertise.) It seems that it would make the tool much more robust. As you mention, it would position it as an alternative to GIA facetware. And because it would not reward steep/deeps and it would give credit to other makes that get dinged unfairly in the GIA system, it seems like it would make the tool even more useful as an "advanced filter" on the GIA system.

A couple of follow-up questions out of curiosity- from the HCA results page is this mention of updates:
"HCA scores were adjusted Dec. 15, 2001 and Feb. 6, 2003"
This would suggest that the tables have not been tweaked since 2003. Is that correct? It seemed to me that I saw a poll you did a year or so ago about fire vs brightness and you mentioned that you were considering re-weighting them in the model.

Also on that page is this statement:
"Even though HCA grades cut more effectively than systems like the AGS, it does not yet factor in symmetry and minor facets."
Was this statement made prior to the release of the AGS LP grading system? Or do you still think HCA grades cut more effectively than the AGS system?

 

[Garry H (Cut Nut)]

Garry,
I have a question about this comment above:
"HCA is near enough but it is not good enough, and if I were to add the minor facets, which is covered in my patent, then you have the GIA system."
Why have you chosen not to add the minor facets? (Not that it would be a simple undertaking but you have available the advanced expertise.) It seems that it would make the tool much more robust. As you mention, it would position it as an alternative to GIA facetware. And because it would not reward steep/deeps and it would give credit to other makes that get dinged unfairly in the GIA system, it seems like it would make the tool even more useful as an "advanced filter" on the GIA system.
Good question Bryan, by the time I got to that point, and started a patent war with GIA that cost serious 6 figures, I had realised through my re-education from Sergey that it was a dead end pursuit. It would have taken 100's of hours (before DiamCalc Pro) to do the minor facet computations (which were relatively easy for the table crown and pavilion stuff) and why? By then I knew that unless you could use this approach fr fancy shapes it was a mikey mouse approach. But yes, I could do it inside a week now with DCpro, but it still is a dead end.

A couple of follow-up questions out of curiosity- from the HCA results page is this mention of updates:
"HCA scores were adjusted Dec. 15, 2001 and Feb. 6, 2003" Leonid and I reworked some data glitches.
This would suggest that the tables have not been tweaked since 2003. Is that correct? It seemed to me that I saw a poll you did a year or so ago about fire vs brightness and you mentioned that you were considering re-weighting them in the model. I have added symmetry bonus and penalty to the Android App which is available from play store. The Apple app - latest from very slow developer 10 minutes ago "The app works in my development environment and on my phone, but when I put into production/the App Store it breaks. This is the last bug I am facing before it is complete.. the email from Apple is me trying to test it in the app store."

Also on that page is this statement:
"Even though HCA grades cut more effectively than systems like the AGS, it does not yet factor in symmetry and minor facets."
Was this statement made prior to the release of the AGS LP grading system? Or do you still think HCA grades cut more effectively than the AGS system?

Yeah!!! very very old. where is it - send it to me and Andrey and we will fix it!!!!
Remember when AGS used a really dumb approach with shallow stones in one corner, deep in the other, and nice thru the diagonal middle. First time I met Pete I told him in my brutal aussie manner why they were wrong and how wrong they were. We sat down with DC and he got it. Check it with him