AGS 2 or AGS 0 - The ''Candidate'' vs Parametric grades

[Garry H (Cut Nut)]

Dear all,

Sometimes I note that people assume the AGS grades on graphs listed on HCA and in other charts from AGS are that - gradings.

They are not.

AGS uses a 3 D scan of a the actual diamond and ray tracing software they developed after the lines of DiamCalc and the 1990''s MSU studies.

The charts from AGS are for the use of cutters to know the safe proportions to get AGS 0. There is some lee way however and if everything is very tight in the sym dept, and any painting digging works with those particular proportions - then stones can be outside those boundaries and still pass the AGS PGS software testing.

Our friend Iiro from Finland sent me this example recently.

So AGS give a parametric guide line to cutters. This differes from GIA and HCA - which are dumb and only work from the paramters as measured by a scanner. GIA do make some allowances for minor facets - but it effects a few stones in a hundred, and I am told the same is true for the grade lowering because of painting or digging. GIA have no way to actually ''measure'' minor or brillianteering effects on optical performance - we were told this at the last Vegas GIA presentation - there is no actual attempt to have a human lookk at a diamond to decide if it is a good one or a baddy.

This is one of the typical major short comings of 4C''s grading of all sorts - the labs rules are skewed to repeatability rather than common sense. It is one reason for example that I like the IGI color grading approach - a well cut round border line J/K could be looked at face up and the grader might upgrade it to K, where-as a radiant would be dropped. This is probably one reason why IGI is seens as softer on color, but it is an attempt to use some common sense.

 

[strmrdr]

Sorry Garry but that's as clear as mud and I know what your talking about.
Can you clarify?

 

[Garry H (Cut Nut)]

Date: 2/16/2007 11:42:21 PM
Author: strmrdr
Sorry Garry but that''s as clear as mud and I know what your talking about.
Can you clarify?

Is this better Storm

The AGS 0 box on HCAis not an AGS grade.

Herre is a diamond that is outside the box, but still gets AGS 0

 

[Paul-Antwerp]

Trying to clarify even more.

If GIA (and other labs) use charts as a result of cut-studies, their cut-grade from then on depends on the charts. In the case of AGS, the charts are different, since they are supposed to be used as guidelines for cutters, not as a grading-chart.

Garry and Iiro here show an example of a stone that, according to the chart is an AGS-2, but the stone being a complete 3D-object and not a combination of only 3 average proportions, the 3D-examination of AGS in their lab gave this stone a performance-grade of AGS-0.

Live long,

 

[strmrdr]

Garry and Paul much much clearer.
Thank you

 

[oldminer]

So the base AGS grade is parametric but the final grade is ray tracing or subjectively applied? I think this highlights the merits of my position which is that direct measurement for the purpose of applying a GRADE is preferable to the approach of AGS. For cutters, a parametric roadmap is very practical.

On a solely parametric basis, a diamond with a grade of AGS 2 could perform as well or possibly better than one which would finds itself parametrically in thee AGS 0 range of the charts. This is a problem for consumers, cutters, appraisers, dealers and everyone else involved. Unless the stone has a final AGS Report, the grade is not known. That, to me, is a troubling result.

 

[JohnQuixote]

Date: 2/17/2007 12:00:33 PM
Author: oldminer
So the base AGS grade is parametric but the final grade is ray tracing or subjectively applied? I think this highlights the merits of my position which is that direct measurement for the purpose of applying a GRADE is preferable to the approach of AGS. For cutters, a parametric roadmap is very practical.

On a solely parametric basis, a diamond with a grade of AGS 2 could perform as well or possibly better than one which would finds itself parametrically in thee AGS 0 range of the charts. This is a problem for consumers, cutters, appraisers, dealers and everyone else involved. Unless the stone has a final AGS Report, the grade is not known. That, to me, is a troubling result.

But I think AGS is providing both aren't they Dave? The cutters receive predictive guidelines...but cutters are very smart and understand what strategies will improve (or harm) a diamond subtly within those broad numbers.

For example, if a piece of rough were best suited to a slightly steep/deep combo it could be cut there - but the cutter could improve that diamond's appearance slightly with a bit of painting...possibly enough to get it a better score than predicted by the basic guidelines. What a great reward: The cutter knows that if he does a nice job with optical symmetry, minor facets & brillianteering in certain proportions sets the skill he contributed to the diamond will not go for nothing...it will be rewarded in the final assessment. In a similar manner, a cutter who uses 'sneaky' tricks is not guaranteed a grade simply because he cuts to X proportions. For example, if he used brillianteering in a deleterious way on that diamond will not receive values high enough to get the grade that was predicted. It will be penalized.

To us it's a great system. The lab educates the upstream manufacturers on what configurations will typically earn the values (all things equal)...but then they hold every diamond individually accountable for earning those values downstream in the final assessment. No diamond gets a 'free ride' simply because its crown and pavilion angles are such-and-such...it is assessed according to all of the facets working together.

I know you support Imagem, so I thought you would see this as a positive (the actual, live, final result - not the predicted result - being assessed). Or maybe I am missing the boat you're on. Throw me a line?

 

[strmrdr]

Here we go getting complicated again.

Personally I feel ray tracing/computer modeling is the best currently available way of grading performance if accurate data is supplied for the models.
That means helium scans which AGS is not using so there will be more error in the results than I would like there to be.
That is neither here nor there with the point Garry is making.

A look up chart can not accurately predict the AGS score.
A look up chart or calculations using averages can not accurately predict diamond performance but can weed out potentially bad combos with a broad brush and some error.
That''s the simply bottom line that we need to keep in mind.

 

[michaelgem]

Maybe I’m wrong and even if I am right either way I’m sure to hear about it. This seems like another instance of a double standard in the Pricescope community in so far as AGS and GIA are concerned. I doubt that the slack being cut here for proportion sets outside the AGS 0 being given an AGS 0 would be similarly applied if GIA were giving Excellent grades to proportion sets outside their Excellent range.

I know that most on Pricescope believe the Excellent range of GIA is already too lenient, so I suspect you would come down hard on GIA should they claim their charts are only guidelines and diamonds outside the Excellent grade will still be given an Excellent grade if the performance metrics warrant it.

GIA went to great pains, time and expense so that what you see from their charts and their diamond grading lab manual is what you get for a grade.

I should think it would be both reasonable and expected that both the grading charts of GIA and AGS should accurately reflect the proportion sets that will attain their top grade and as well the proportion sets that will not. As a cutter, do you have to have a divining rod in addition to the charts to predict whether your diamond will get the top grade?

I know the answer to that question. If you really want to know whether your diamond will get a zero you will have to buy a Sarin Machine and the AGS software to find out. What an uproar would be raised on Pricescope if the GIA had the same requirement.

Michael Cowing

www.acagemlab.com

PS: From the Sarin website: “The cooperation between the two entities (AGS and Sarin) does not end here — AGS and Sarin expect to soon announce an agreement granting Sarin distribution rights to the AGS Performance Grading Software (PGS) used to grade polished stones according to the new AGS cut grading system.” Wish I had stock in Sarin.

 

[strmrdr]

Garry started this thread because people were concerned because their AGS0 diamond wasn''t in the AGS0 box on the HCA result chart.
The box is based on the cutting guidelines not the grading results.

Now we are getting into the same old same old ags vs gia arguements and its going to make the very people this thread was aimed at tune out so can we please take it elsewhere to fight about AGS vs GIA vs Light boxes?
Thanks!

 

[michaelgem]

Date: 2/17/2007 10:46:12 PM
Author: strmrdr
Garry started this thread because people were concerned because their AGS0 diamond wasn''t in the AGS0 box on the HCA result chart.
The box is based on the cutting guidelines not the grading results.

Now we are getting into the same old same old ags vs gia arguements and its going to make the very people this thread was aimed at tune out so can we please take it elsewhere to fight about AGS vs GIA vs Light boxes?
Thanks!

Agreed. You are welcome. Forget the pro AGS anti GIA bias.

The following is still germane to this topic.

I should think it would be both reasonable and expected that both the grading charts of GIA and AGS should accurately reflect the proportion sets that will attain their top grade, and as well the proportion sets that will not. As a cutter or consumer you should not have to have a divining rod in addition to the charts or have to purchase a Sarin machine and the AGS Performance Grading Software (PGS) to predict whether your diamond is a top grade. IMO that is what the charts of AGS and GIA originally were intended to convey and should convey.

Michael Cowing

 

[JohnQuixote]

 

[Serg]

Michael,
Optical appearance grade depends from much more factors then Crown, Pavilion and Table, symmetry grade and other average parameters
If you use optical grade you can not follow charts.

If you use parametrical grade you can follow charts.

AGS use optical grade , and develop chars for reference just.
GIA use parametrical grade.

 

[Paul-Antwerp]

Date: 2/18/2007 12:14:07 AM
Author: michaelgem

The following is still germane to this topic.

I should think it would be both reasonable and expected that both the grading charts of GIA and AGS should accurately reflect the proportion sets that will attain their top grade, and as well the proportion sets that will not. As a cutter or consumer you should not have to have a divining rod in addition to the charts or have to purchase a Sarin machine and the AGS Performance Grading Software (PGS) to predict whether your diamond is a top grade. IMO that is what the charts of AGS and GIA originally were intended to convey and should convey.

Michael Cowing

Michael, please read Serg''s comment again. It is exactly to the topic, and very important.

To take it further, what you call a ''grading chart'' of AGS, is not a grading chart. It is a guideline to cutters, to make life easier for them. If you use it as a grading chart, or think about it as a grading chart, you did not read the bottomline.

Live long,

 

[oldminer]

If one uses charts for cutters that is a good thing.
If one uses ray tracing for grading, it is not such a good thing.

You can do better than using ray tracing. Better is out there and works well in spite of where the major labs have chosen to go. The ImaGem device has evolved quirte a bit since many of you last saw or used it. I encourage people who might consider a better method of grading to visit or to re-visit the VeriGem device which now incorporates motion and multiple readings for much higher repeatability than its earliest commercial model.

 

[Serg]

Date: 2/18/2007 11:40:10 AM
Author: oldminer
If one uses charts for cutters that is a good thing.
If one uses ray tracing for grading, it is not such a good thing.

You can do better than using ray tracing. Better is out there and works well in spite of where the major labs have chosen to go. The ImaGem device has evolved quirte a bit since many of you last saw or used it. I encourage people who might consider a better method of grading to visit or to re-visit the VeriGem device which now incorporates motion and multiple readings for much higher repeatability than its earliest commercial model.

re:If one uses ray tracing for grading, it is not such a good thing.

Dave,
Please explain. Why is it not such good thing.
Please compare:
If one uses Imagem for grading, it is not such a good thing.
Do you like such type debate?
BTW. What is about accuracy Imagem?
until now we do not receive any explanation huge error in Imagem device.

 

[oldminer]

This is not a thread on the topic Serg would like to discuss, but I mentioned imporvements in ImaGem that have happened since the error he believes existed. Because of the limitaions of ray tracing, it is a better strategy to measure directly. A direct measure is always the preferable way to "grade" wheneven possible. There is NO example in the world of a direct measure being held secondary to a calculated measure when it comes to grading. Or, does someone have such an example to suggest? I have been told that there is no such example, but maybe my sources don''t have all the answers. I''d be willing to learn about such an unusual grading system if it does exist.

Once labs have confidence in direct measurement of light, they will likely switch to using it. It is far simpler and more flexible than calculating light behavior, especially when it comes to fancy shapes.

 

[michaelgem]

Serg and Paul,

I do appreciate your points and I understand that the guideline charts are labled as guidelines.

I am well aware, as are you, of the advantages and shortcomings of both AGSLs and GIAs grading systems. Feasibility in a production diamond grading environment results in some cut grading trade offs and compromises. Because of the pluses and minuses it is easy to either defend or criticize either system.

I choose to maintain a neutral stance. I also choose to provide a counter balance to the bias that most on Pricescope evidence when they jump to the defense of AGS whenever issues like this come up. It is clear that with all its defenders, AGS has no need of any additional praise on Pricescope from me. And I do have mostly praise for AGSLs grading system. Both Al Gilbertson and I contributed to the early stages of its development.

I will make my only point on this subject by using a combination of a 41 degree pavilion angle and a 35 degree crown angle in the context of a 56% table, 80% lower half length, 55% star length and a medium girdle. The AGS cutting guideline charts indicate this diamond is an AGS 2, two grades away from a zero. This was of interest to me as this combination of 41 degrees and 35 degrees is rather famous. It was attributed to the American Ideal of Henry Morse back in 1916 by Frank Wade and Herbert Whitlock in their respective books on diamonds. Peter kindly ran this full set of proportions for me and let me know that it attained a zero grade.

Since the intent of the cutting guideline charts is to guide the cutter to obtain a zero, and the 41 degree and 35 degree combination of the American Ideal of Henry Morse is a zero, I think the guideline charts should so indicate. Otherwise, by dissing this famous combination as an AGS 2 the charts appear to be misguiding rather than guiding.

Please do not give me the rejoinder that the guideline charts are helping the cutters by playing it safe and reporting conservative combinations. I know cutters like to play it on the "edge" and they want to know where that edge really is.

How about it people? Is this an unreasonable suggestion? All it would take is a batch rerun of the pavilion and crown angle combinations for the common table sizes in the context of 80% lower girdle length, 3.5% girdle thickness at the mains, and 55% star length. How difficult can that be?

Michael Cowing

 

[Garry H (Cut Nut)]

Date: 2/17/2007 10:25:12 PM
Author: michaelgem

Maybe I’m wrong and even if I am right either way I’m sure to hear about it. This seems like another instance of a double standard in the Pricescope community in so far as AGS and GIA are concerned. I doubt that the slack being cut here for proportion sets outside the AGS 0 being given an AGS 0 would be similarly applied if GIA were giving Excellent grades to proportion sets outside their Excellent range.

I know that most on Pricescope believe the Excellent range of GIA is already too lenient, so I suspect you would come down hard on GIA should they claim their charts are only guidelines and diamonds outside the Excellent grade will still be given an Excellent grade if the performance metrics warrant it.

GIA went to great pains, time and expense so that what you see from their charts and their diamond grading lab manual is what you get for a grade.

I should think it would be both reasonable and expected that both the grading charts of GIA and AGS should accurately reflect the proportion sets that will attain their top grade and as well the proportion sets that will not. As a cutter, do you have to have a divining rod in addition to the charts to predict whether your diamond will get the top grade?

I know the answer to that question. If you really want to know whether your diamond will get a zero you will have to buy a Sarin Machine and the AGS software to find out. What an uproar would be raised on Pricescope if the GIA had the same requirement.

Michael Cowing

www.acagemlab.com

PS: From the Sarin website: “The cooperation between the two entities (AGS and Sarin) does not end here — AGS and Sarin expect to soon announce an agreement granting Sarin distribution rights to the AGS Performance Grading Software (PGS) used to grade polished stones according to the new AGS cut grading system.” Wish I had stock in Sarin.

Michael I very much doubt those so called American Ideal cuts would recieve a good grade from AGS or GIA because they had very short lower girdle facets. Perhaps for the lighting and spectacle quallity''s of the day they were very good at making fire, which AGS have a measure - but not one that I find overly impressive.

Many vendors will suply 3D scans of diamonds - so you do not need a scanner

Finally - I am criticising HCA in the same breath as GIA''s proportion or parametric system

 

[adamasgem]

Date: 2/18/2007 12:55:05 PM
Author: oldminer
This is not a thread on the topic Serg would like to discuss, but I mentioned imporvements in ImaGem that have happened since the error he believes existed. Because of the limitaions of ray tracing, it is a better strategy to measure directly. A direct measure is always the preferable way to ''grade'' wheneven possible. There is NO example in the world of a direct measure being held secondary to a calculated measure when it comes to grading. Or, does someone have such an example to suggest? I have been told that there is no such example, but maybe my sources don''t have all the answers. I''d be willing to learn about such an unusual grading system if it does exist.

Once labs have confidence in direct measurement of light, they will likely switch to using it. It is far simpler and more flexible than calculating light behavior, especially when it comes to fancy shapes.

Dave..Labs MIGHT use light performance "measurements", however no one has seen these paradigms versus published AGS, GIA, HCA, etc.. And light return, or "brilliance" is only one part of the puzzle, fire, scintillation contribute also. AND the resultant paradigms are directly effected by the lighting environment chosen to define the grading system.

I would like to know what envirionment these "measurements" are made in, and how does it relate to the published criteria AGS or GIA or HCA uses.

All "measurements" have uncertinties, whether they be measurements of light return, or dimensional measurements translated to a theoretical light performance metric.

I hav NOT YET SEEN paradigm comparisons.. It would be interesting to compare, lets say, IMGEM, versus AGS versus GIA. Are you will to provide same? Pretty please.

Where are the IMAGEM cut guidelines.

This whole thing is in its'' infancy and constantly improving (with the notatble exception of FarceWare).

 

[Paul-Antwerp]

Date: 2/18/2007 6:02:28 PM
Author: michaelgem

Serg and Paul,

I do appreciate your points and I understand that the guideline charts are labled as guidelines.

I am well aware, as are you, of the advantages and shortcomings of both AGSLs and GIAs grading systems. Feasibility in a production diamond grading environment results in some cut grading trade offs and compromises. Because of the pluses and minuses it is easy to either defend or criticize either system.

I choose to maintain a neutral stance. I also choose to provide a counter balance to the bias that most on Pricescope evidence when they jump to the defense of AGS whenever issues like this come up. It is clear that with all its defenders, AGS has no need of any additional praise on Pricescope from me. And I do have mostly praise for AGSLs grading system. Both Al Gilbertson and I contributed to the early stages of its development.

I will make my only point on this subject by using a combination of a 41 degree pavilion angle and a 35 degree crown angle in the context of a 56% table, 80% lower half length, 55% star length and a medium girdle. The AGS cutting guideline charts indicate this diamond is an AGS 2, two grades away from a zero. This was of interest to me as this combination of 41 degrees and 35 degrees is rather famous. It was attributed to the American Ideal of Henry Morse back in 1916 by Frank Wade and Herbert Whitlock in their respective books on diamonds. Peter kindly ran this full set of proportions for me and let me know that it attained a zero grade.

Since the intent of the cutting guideline charts is to guide the cutter to obtain a zero, and the 41 degree and 35 degree combination of the American Ideal of Henry Morse is a zero, I think the guideline charts should so indicate. Otherwise, by dissing this famous combination as an AGS 2 the charts appear to be misguiding rather than guiding.

Please do not give me the rejoinder that the guideline charts are helping the cutters by playing it safe and reporting conservative combinations. I know cutters like to play it on the ''edge'' and they want to know where that edge really is.

How about it people? Is this an unreasonable suggestion? All it would take is a batch rerun of the pavilion and crown angle combinations for the common table sizes in the context of 80% lower girdle length, 3.5% girdle thickness at the mains, and 55% star length. How difficult can that be?

Michael Cowing

Dear Michael,

If you start with the premise that individuals and even a group of people are biased, you are losing the objectivity which is necessary to research. There is even the risk that you could become inclined to weigh arguments to the contrary more heavily, which carries the risk of bringing you into the technique, which I know as demagogy.

First, the topic of this thread is not about AGS vs GIA, it is merely a re-iteration of the fact that one should not blindly use the AGS-cutting-charts as grading-charts. For some reason, you want to turn it into a criticism of AGS.

Now for your points:

1. In your first thread, you accuse AGS of double-standards, because their grading-charts are not in line with the actual lab-procedure. Now, you say that you are well aware that the charts are not grading-charts, but cutting-guidelines. If you are so well aware of that, why do you then bring it forward differently?

2. Here, as an example, you bring forward a proportion-combination, which according to you, the cutting-guidelines indicate as AGS-2, while your personal communication with AGS indicates that they would give it a 0-grade. Again, this is a mis-representation of facts.

If you look at the cutting-guidelines, they clearly indicate that these are for 80% lower-girdle lenght, 50% star lenght, 3.5% girdle thickness at the mains, and for a specific diameter. If you are saying that the Morse-proportion-set indicates AGS-2, you are only talking about the cutting-guidelines for 6mm. On the guidelines for 4mm, 8mm, 10mm and 12mm., the charts indicate AGS-1.

With a different star lenght, and not knowing what size of stone we are talking about, it is entirely possible that the lab-grading of this stone is 0, while the cutting-guidelines indicate 2 or 1. This is exactly the point of this thread.

As a summary, you are definitely entitled to your personal opinion, and I welcome you to voice it, but in doing so, I would appreciate it if you gave all the facts and avoid playing with words.

Live long,

 

[michaelgem]

Dear Paul,

I want to apologize for combining my thoughts about the guideline charts with my useless tirade about bias on PriceScope. It was equivalent to trying to tell Diane Sawyer or CNN that they lean a bit to the left of center in their reporting. I should have known that raising such contention would obscure my more reasoned concerns.

You would think that I would have learned by now that nothing is ever accomplished by confrontation. It only causes alienation. My best acquaintances in the diamond world are major contributors to this forum, and I am sorry if I offended any of them.

What was lost in my tirade was that I do have mostly praise for AGSLs grading system. Both Al Gilbertson and I contributed to the early stages of its development, so any of my criticisms/suggestions feel to me a little like a parent criticizing the looks of his child.

So I apologize especially to Paul and the other posters to this thread. I am going back and rewrite my comments and suggestions concerning the guideline charts in a more diplomatic fashion the way I should have written them initially.

Michael Cowing

 

[Garry H (Cut Nut)]

Well written reply Paul.
Lets see if I can lower the tone a little as usual?

Date: 2/19/2007 11:48:11 AM
Author: michaelgem

Dear Paul,

I want to apologize for combining my thoughts about the guideline charts with my useless tirade about bias on PriceScope. It was equivalent to trying to tell Diane Sawyer or CNN that they lean a bit to the left of center in their reporting. I should have known that raising such contention would obscure my more reasoned concerns.

Why would you imagine Paul (or Sergey or anyone else who lives where 3/4''s of the population live) would have any idea about what you just wrote )ichael?

You would think that I would have learned by now that nothing is ever accomplished by confrontation. It only causes alienation. My best acquaintances in the diamond world are major contributors to this forum, and I am sorry if I offended any of them.

What was lost in my tirade was that I do have mostly praise for AGSLs grading system. Both Al Gilbertson and I contributed to the early stages of its development, so any of my criticisms/suggestions feel to me a little like a parent criticizing the looks of his child. Thank you Michael.

So I apologize especially to Paul and the other posters to this thread. I am going back and rewrite my comments and suggestions concerning the guideline charts in a more diplomatic fashion the way I should have written them initially. Just as in a technical journal or web version there-of, it is innappropriate to edit ones words after posting and force others to edit their rebuttals. You have been participating in forums long enough to know that this would be poor form, so please leave your posts alone, and if you feel a need to change history, please do it in the future, not the past Michael.

Michael Cowing

 

[michaelgem]

The charts published by AGS are labled “cutting guideline charts”. It is very clear from this title that their intent is to guide the cutters in obtaining the AGS Ideal 0 cut grade. Out of the economic necessity to maximize return on investment, diamond cutters need more than the conservative guideline charts, as they now exist. This is why cutters wishing to cut to the highest AGS Ideal 0 standards invest in the Sarin and the AGSL’s grading software. They need to know the constraints on proportions required to obtain an AGS Ideal 0 with more accuracy than the charts currently provide.

Today’s cutters are capable of cutting to great precision to both maximize yield and at the same time obtain Ideal beauty and optical performance by adhering to the constraints necessary to obtain an AGS Ideal 0. They need to know those constraints with better precision than is offered by the current guideline charts.

Cutting a modern Ideal round brilliant to the 41 degree and 35 degree combination of the early American Ideal of Henry Morse for a 6mm stone with 50% star length, 80% lower girdle length, 3.5% girdle thickness at the mains will get you an AGS 2 according to the charts. It will also get you a GIA Excellent. When I asked Peter about this, he kindly ran this full set of proportions for me and let me know that it attained a zero grade.

So the charts were misleading in this instance to the extent of 2 grades, and Peter informs me that in general the Ideal 0 grade is somewhat wider than the guideline charts indicate. I reason that AGS would be doing the cutters a favor by updating those charts to better reflect the combinations such as this 41/35 case that are actually an Ideal 0 and not a 1 or 2.

This would additionally clear up confusing cases like Morse’s Ideal angles, which from the charts of GIA and AGS appear to be points of contention, when in truth they are actually points of mutual agreement.

Michael Cowing

 

[Regular Guy]

Date: 2/19/2007 2:07:08 PM
Author: michaelgem

This would additionally clear up confusing cases like Morse’s Ideal angles, which from the charts of GIA and AGS appears to be points of contention, when in truth they are actually points of mutual agreement.

Michael Cowing

Have been following this thread with interest...and am as interested as the next guy in finding points of mutual agreement. Sounds like you''ve found one scenario, as described in your most recent post, Michael, to square this, and also, suggesting a change in charts posted may be required. I have no observational value added to contribute, but enjoy following the logical consequences of these discussions.

I do have to wonder, though, if it''s possible your discussion with Peter may have happened before the new AGS set of charts, which would also serve to explain, and we could just call this a bad game of telephone. See this thread, for example, showing 35 & 41 as included in the old AGS0.

Otherwise, as a frequent reader here, I do attend to the 41 pavilion angle being discussed frequently with a tone of some controversy associated with it. Enter it into the search bar above, and you''ll max out on hits. Even the Queen Mother does not like it, and in the same discussion, it seems Dave Atlas is not a big fan, anyway. I saw the 41 referenced at your site, associated with a sweet spot, but believe your crown angle there is 34.5, which probably makes life easier, but I don''t know too well about these things...and have been so well behaved up to now as to avoid sticking my nose into this topic, but decided to step in after all.

BTW, Garry has actually touched on this point before, here, in my post on the subject, where I''m happy to take on AGS as well, such that it''s worth. In the end, from the point of view of finding value in helping people shop well, I do land in favor of both AGS''s approach, and Garry''s intent here to clarify. I think the main point here is clearly that AGS includes more information in its AGS0, such that crown & pavilion angles should not be taken as a proof text. Consideration of whether a particular set of crown & pavilion angles, in the main, do make for the new AGS0 seems a tangent in that regard...however, one I thought to meet. That I can only do this by way of third party comment, I apologize for...but not too much. The board is free, and on the chance this speculation is right, I''m giving it a shot.

Regards,

 

[Paul-Antwerp]

Dear Michael,

I hate to correct the words of people that I respect, and I hate to do that more than once a day.

However, I hate it even more if people try to put themselves in my shoes. Please do not try that.

You are claiming that I need to invest in Sarin and AGS-grading-software, while we are using neither of them. In the way that you are claiming your point, you make it seem that the mere fact of obtaining the AGS-0-grade is the nec plus ultra. I am very sorry, but from our side, we keep on raising the point that AGS-0 is only the beginning of the story, not the end.

In other words, the fact that our stones fetch the 0-performance grade is only a positive side-effect. It is not the point of the design, and it is not ever a consideration in deciding upon a proportion-set. In this matter, you may talk about dozens of other cutters, but I would prefer if you tried not to mention us in this regard.

On another note, when talking about Morse''s proportion-set, please take into consideration the era when these were set. Did one have the ability to measure up to a tenth of a degree in those days, and more importantly, did one have the ability to cut up to that degree? Considering that most cutters cannot cut up to that degree today, I think that we do not need to take this into further detail.

So, did Morse have 50% stars or 55% stars? With which girdle thickness? And did he really have 80% LGF''s?

Live long,

 

[michaelgem]

Dear Paul,

When I said “This is why Ideal cutters like Paul invest in the Sarin and the AGSL''s grading software,” I meant Ideal cutters who like yourself cut to the highest standards of Ideal. It was a complement to the standards you set for yourself and the quality of your product, not an attempt to put myself in your shoes.

I will remedy this by substituting “This is why cutters wishing to cut to the highest AGS Ideal 0 standards invest in the Sarin and the AGSL’s grading software”

You mention that you are using neither the Sarin nor the AGS grading software, while your comments on the fact that 41/35 gets a 2 or 1 depending on diamond diameter indicates that you must at least own or have access to the AGS software. I will be amazed if you tell me you obtain AGS Ideal 0 quality and better without the aid of a Sarin or like scanner such as the Megascope or Helium machines. If so, that is a great tribute to your skill as a cutter and/or the advances in diamond cutting gear such as the modern dops and tangs.

On your other note and question:

My investigation into the Morse angles of 41 and 35 applied to the modern Ideal with larger table, and longer top and bottom halves was how I first learned that the cut grading guideline charts did not reflect the true range of the AGS Ideal 0. That is why I chose that combination to illustrate my point and suggestion.

Even though Morse had a table under 50% and bottom halves that were too short, he was the first in history to cut to crown and pavilion angles now considered Ideal. This was back in 1860, over a half-century before Tolkowsky’s book Diamond Design. Prior to Morse the best crown and pavilion angles as documented by Mawe, Tillander and others were believed to be 45 degrees on both crown and pavilion. In light of today’s raytracing we now know that 45 degrees on the pavilion creates retroflection and the nail-head appearance. So the best pavilion angle prior to Morse was actually the worst possible angle from today''s perspective.

As in your closing, I also wish you a long and prosperous life.

Michael Cowing

 

[strmrdr]

Since this is pretty much off topic anyway.....

Something to keep in mind when talking about old cuts and the ideal cut for varies times is that the nature of indoor lighting has change a lot and who wears diamonds has also changed.
The older cuts had larger chunkier facets to go with the soft lights of the day, candle, torch and lamp light that the rich would find themselves in at parties which is when they wore most of the jewelery.
Day in and day out very very few people wore diamonds.
Today''s lighting is more varied than ever and in some ways a lot harder to get decent performance under.
With the push to cfl lighting under way its going to get worse because they frankly suck for diamond performance.
Some states are already looking into laws requiring them to be used in all new construction.

 

[michaelgem]

Ira,

I remember you as one of the incredibly astute observers and commentators like strmrdr on the PriceScope forum. Your post in my regard gets an Excellent and an AGS Ideal whichever you like best.

The old AGS Ideal 0 set the range of Ideal independently for each parameter. Specifically, from 40.2 to 41.2 for pavilion angle and 33.75 to 35.8 for crown angle. This creates a rectangular Ideal 0 ‘sweet spot’ (as I like to call it) of Ideal crown and pavilion angle combinations. AGS was criticized, because this rectangular sweet spot included steep/deep combinations and shallow/shallow combinations thought to be less than ideal.

Their new performance based system clips off those steep/deep and shallow/shallow combinations, throwing them out of the Ideal 0 category, and creating a skinnier sweet spot. It has an orientation along about a -4.5 to 1 negative sloping line that I refer to as the AGS Axis of Ideal (because a skinny ellipse fit to the Ideal sweet spot would have a major axis of approximately –4.5 to 1.)

Unfortunately, IMO some combinations such as the slightly steep/deep Morse combination of 41/35 were an unintended consequence of the steep/deep trimming. That is why it appears in the guideline charts as an AGS 2. AGS has righted this by slightly widening the Ideal 0 sweet spot to now include this combination and others in the Ideal 0 sweet spot range.

That is why I reasoned that AGS would be doing the cutters a favor by updating those charts to better reflect the combinations such as this 41/35 case for a 56% table that are actually an Ideal 0 and not a 1 or 2 under the listed conditions of 50% star length, 80% lower girdle length, and 3.5% girdle thickness at the mains.

Cheers,

Michael Cowing

 

[Garry H (Cut Nut)]

Michael the entire issue you have raised seems like some USA "we were on the moon first" complaint or claim.
And it is completelty unrelated to the topic I started.

Morses 45% table size, the above mentioned lower girdles and satr lengths - what are you really discussing here?

Secondly - like GIA - the real problem is the AGS chart has too wide a step - 0.2 degrees pavilion is crazy as it corresponds to the equivalent jump of 1.0 degree crown from a level of optical importnace. This would do the most to fix the problem.

But finally when Peter ran your completley modernised data - he ran a perfectly symmetrical stone. We know that there are 2 problems with that - Only Paul cuts puurrrfectly symetrical diamonds (with perfect polish and sauve swash buckling), and the variation in scans azimuth is inadequate and introduces as much as a 5% error (in my understanding).