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

[michaelgem]

Hi Garry,

I just used 41 and 35 as the one example that I knew of from personal experience. It was an Ideal 0 even though the cutting guidline charts said it was an AGS 2.

I thought your thread related to a similar disparity between these published charts and the actual grade, which is what got me started on all this.

Your right in saying that these charts assume perfect symmetry that is not usually obtained in practice except by super Ideal cutters like Paul.

My comment and suggestion repeated below is carefully stated and unambiguous, and it is in the context of diamonds that are cut with sufficient craftsmanship that symmetry is not the issue affecting whether the combination gets a 0 or a 2.

I reason that AGS would be doing the cutters a favor by updating their 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 as their charts currently indicate.

This is still in the context of the listed conditions of 50% star length, 80% lower girdle length, and 3.5% girdle thickness at the mains.

Cheers,

Michael Cowing

 

[Serg]

re: 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,

If you want be neutral stance you SHOULD remember history.
1) AGS give charts before new grading.( For round firstly, then Prin., now emerald) Is it right?
2) GIA started new grade, and had sold DATABASE through SARIN and OGI only. cost for one license was +-3000$. ( For example for Octonus was not easy even receive rules for such type business relationship with GIA instruments. final rule was: OctoNus should proof what OctoNus happy(happy follow GIA goals and rules) work with GIA, then GIA will send rules. or something similar. I do not remember exactly, it was very long correspondence just for receive RULES!
3) After long time and big pressure from different sides, GIA published charts( firstly they try use Facetware internet version. which is difficult for use by cutters.) BTW I published example on pricescope( FacetWare from sarin gave grade VG( please correct me if I am wrong) Final GIA grade was Poor!

 

[Paul-Antwerp]

Date: 2/19/2007 5:12:20 PM
Author: 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.
Michael Cowing

Sorry Michael,

I think that I need to clarify this.

When designing a stone, as in choosing for a specific goal-set of proportions, we indeed do not use neither Sarin or AGS-grading software. The latter, we do not use at all.

The Sarin (or similar) is used in scanning the rough, and that scan in combination with the experience ,the eyes and the brains of five highly trained leads to a decision on how to attack that specific rough stone. But that has nothing to do with the choice of the goal-proportion-set. And then, it comes down to tools and mastering them. I have never seen a Sarin (or similar) cut a stone.

Of course, we are probably an exception as we are not interested in the bottom-area of the AGS-0-grade. We wish to cut in the top-quality area of AGS-0, and as such, your example of Morse-proportions does not really interest me.

However, we do have the AGS-cutting guidelines for various sizes, and that is where I deducted that your example has different basic scores depending upon the diameter. Not from any software.

Live long,

 

[Paul-Antwerp]

Date: 2/19/2007 8:39:07 PM
Author: 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).

Garry, may I thank you for that compliment.

And indeed, I can definitely foresee the situation in which 95% of cutters would attack that 41.0/35.0-combination, and AGS would grade their effort as AGS-1 or 2. While if we would have a go at it, it would very possibly obtain the 0-grade.

In a very similar way, GIA originally was labeling some proportion-combo''s as very good (possibly based on real-life-observation of mostly unsymmetrical stones with those combo''s), while if these combo''s are cut in a very symmetrical way, they are exactly the absolutely highest performers ever (remember Bruce Harding, and cutting close to the edge). It was one of our criticisms of the GIA-system, and I have the impression that they widened the EX-range in that particular area. The result now is that all the combo''s with this average proportion-set are GIA-EX, while only the very symmetrical ones really deserve that.

Anyway, the systems are as they are, and before we criticize them, it is important that we understand them.

Live long,

 

[JohnQuixote]

A word or two about the AGS cutting guideline charts: These are “guidelines” for manufacture and the charts were published exactly as compiled from perfectly formed virtual stones.In fact, only proportions sets that had absolutely no deductions of any kind were published as 0s. For instance, if the virtual stone received a deduction of 0.01 for brightness and a deduction of 0.01 for dispersion, it shows up on the guideline chart as a potential cut grade of 2.The lab understands that this is erring on the strict side, and may be seen as ‘unfair’ to some proportions sets.This is why, from day one, the AGS has told us again and again that the boundaries are ‘fuzzy’.

The lab extensively studied actual stones to see how accurately cutters could cut. Based on those studies, they set the amount of ‘fuzziness’ for the actual grading system. So…an actual stone may get a deduction of 0.1 for brightness and 0.3 for dispersion for a total of 0.4 and that stone will still get a 0 in light performance. The performance grade is rounded up at 0.5’s. So, 0.5 becomes a 1, 1.5 becomes a 2 etc. On the other hand, you can have a stone that sits in the ‘heart’ of 0 on the guideline proportions charts and because of a cutting problem (out of roundness, deleterious digging or painting, etc.) it could get a contrast deduction of 0.3 and a leakage deduction of 0.21 and then it would receive a 1 in light performance.

In the final test a stone can be on the boundary and get a better grade or a worse grade depending on how good a job the cutter did in making the stone. It’s determined by the ray tracing values of the 3D scan.It is a fact that this system does push the limits of today’s scanning devices.The AGS takes the position that these devices will get better and more accurate over time, and they prefer to be on the leading edge rather than the trailing edge.

When we’re posting on a consumer forum it’s important to reiterate that these guideline charts were created for manufacturers - not diamond buyers - in order to provide the industry with realistic and practical areas to cut.In a lab sense I see this as similar to the philosophy of master color stones:A lab’s master color stone is at the strictest end of its bandwidth.If a diamond being graded falls between the G and H master stones it still earns a G.It only falls to H if it is equal to or below the H master color stone. Edited to add: Certainly subjectivity and standards may differ between the labs/master stone positioning/etc. Without getting off on a color grading tangent, my point is to illustrate that, similarly, these cutting guideline charts are set at the strictest end of what is predicted to get the light performance grade.

 

[michaelgem]

I do not want to belabor my suggestion, so this will be my last attempt to be heard.

Paul commented: "Anyway, the systems are as they are, and before we criticize them, it is important that we understand them."

My suggestion is given in the spirit of wanting a better understanding of the AGS Ideal 0 range.

I know that the guideline charts are for mathematically symmetrical diamonds with the listed conditions of 50% star length, 80% lower girdle length, and 3.5% girdle thickness at the mains.

AGS tells us that the Ideal 0 grade is somewhat wider than the current guideline charts indicate, but we do not know how much wider. Am I the sole member of PriceScope that thinks AGS would be doing the cutters and us a favor by updating those charts? I would like to see them better reflect the combinations such as the 41/35 case that are actually an Ideal 0 and not a 1 or 2. At the very least this is of academic and educational interest. As Paul said "It is important that we understand them"

Is it an imposition to do 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 50% star length just as AGS did to generate the current charts?

Michael Cowing

 

[Garry H (Cut Nut)]

Date: 2/21/2007 12:17:32 AM
Author: michaelgem

I do not want to belabor my suggestion, so this will be my last attempt to be heard.

Paul commented: ''Anyway, the systems are as they are, and before we criticize them, it is important that we understand them.''

My suggestion is given in the spirit of wanting a better understanding of the AGS Ideal 0 range.

I know that the guideline charts are for mathematically symmetrical diamonds with the listed conditions of 50% star length, 80% lower girdle length, and 3.5% girdle thickness at the mains.


AGS tells us that the Ideal 0 grade is somewhat wider than the current guideline charts indicate, but we do not know how much wider. Am I the sole member of PriceScope that thinks AGS would be doing the cutters and us a favor by updating those charts? I would like to see them better reflect the combinations such as the 41/35 case that are actually an Ideal 0 and not a 1 or 2. At the very least this is of academic and educational interest. As Paul said ''It is important that we understand them''


Is it an imposition to do 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 50% star length just as AGS did to generate the current charts?

Michael Cowing

Great idea Michael,

Would you like that with the extreme boundary of symmetry effects, with a little painting or digging, and ranch dressing?

 

[adamasgem]

Date: 2/21/2007 1:54:47 PM
Author: Garry H (Cut Nut)

Great idea Michael,

Would you like that with the extreme boundary of symmetry effects, with a little painting or digging, and ranch dressing?

Well done Garry.. Hope he gets the point...

 

[michaelgem]

Hi Garry,

Re: Would you like that with the extreme boundary of symmetry effects, with a little painting or digging, and ranch dressing?

Perhaps you skimmed over my last attempt to communicate my suggestion and missed it. I did say how I would like it.

"I know that the guideline charts are for mathematically symmetrical diamonds with the listed conditions of 50% star length, 80% lower girdle length, and 3.5% girdle thickness at the mains."

That''s how the the current guideline charts were generated, which reflect the initial AGS Ideal 0 boundaries. These boundaries have been relaxed, but to what extent remains unsaid.

I would like to see the charts better reflect the combinations such as the 41/35 case that are actually an Ideal 0 and not a 1 or 2. At the very least this is of academic and educational interest. As Paul said "It is important that we understand them"

That''s without painting, digging, or ranch dressing.

Ideal regards,

Michael

 

[michaelgem]

One other thought. Billing these quideline charts as conservative to maximize the likelihood that a cutter less competent than Paul will still get a zero seems to be selling the profession a little short.

If I am a cutter walking the Ideal 0 line, I have a better chance of not falling off if I know where the edge is. Even if that edge is predicated on an optically or mathematically symmetric stone. IMO It should be up to the cutter, knowing his own skill level, not AGS, to decide how close to the edge he wants to play. He can''t do that if he is not told where the Ideal 0 edge is.

Michael Cowing

 

[strmrdr]

Date: 2/21/2007 2:54:09 PM
Author: michaelgem
One other thought. Billing these quideline charts as conservative to maximize the likelihood that a cutter less competent than Paul will still get a zero seems to be selling the profession a little short.

Michael Cowing

I have a lot of respect for your work but loving very tight symmetrical stones and keeping an eye out for them the cutters that can on a consistent basis hit a narrow target with tight stones whose stones get into the hands of the PS vendors that iv seen the data for can be counted on one hand. So I have to disagree.

1: Paul
2: GOG classic cutter1
3: GOG classic cutter2
4: isee2''s latest cutter
Are all that I have ran across for rounds that can do it.

 

[adamasgem]

Date: 2/21/2007 3:23:46 PM
Author: strmrdr

Date: 2/21/2007 2:54:09 PM
Author: michaelgem
One other thought. Billing these quideline charts as conservative to maximize the likelihood that a cutter less competent than Paul will still get a zero seems to be selling the profession a little short.

Michael Cowing

I have a lot of respect for your work but loving very tight symmetrical stones and keeping an eye out for them the cutters that can on a consistent basis hit a narrow target with tight stones whose stones get into the hands of the PS vendors that iv seen the data for can be counted on one hand. So I have to disagree.

1: Paul
2: GOG classic cutter1
3: GOG classic cutter2
4: isee2''s latest cutter
Are all that I have ran across for rounds that can do it.

I agree with Storm (there are others here that do good work, however) and disagree with Cowing..

Why anyone, a cutter, would try to cut a stone on a borderline, is beyond me.

Conservative charts serve the cutter better as something to strive toward.

The charts are not meant as absolute grading charts, period.

And the difference is, with respect to Farceware(TM), is that, even though the averages may be within the GIA EX paradigm (hell, most stones probably fall into their wide bucket), the stone may still be a dog in AGS''s opinion, based on ray tracing the actual stone, just as stones whose averages fall within AGS''s 0 paradigm, may not get the "expected" AGS grade because of cutting imbalances.

Sorry Michael, you can''t use the charts to grade stones..

 

[RockDoc]

RE: Dealers cutting tight symmetrical stones.


What about Eightstar & Whiteflash, Storm?

And how about some of the stones from Hearts on Fire and Blue Nile''g Signature Collection?


Do you think they''re cutting chopped liver?

Paul, GOG''s suppliers, and ISEE2 don''t have a "lock" on well executed symmetry.

Correct me if I''m wrong, perhaps I misunderstand your point, but you seem to infer that the above are the ONLY people cutting symmetry well. Not Factual if that is what you meant!

Rockdoc

 

[WinkHPD]

Date: 2/21/2007 2:54:09 PM
Author: michaelgem
One other thought. Billing these quideline charts as conservative to maximize the likelihood that a cutter less competent than Paul will still get a zero seems to be selling the profession a little short.

If I am a cutter walking the Ideal 0 line, I have a better chance of not falling off if I know where the edge is. Even if that edge is predicated on an optically or mathematically symmetric stone. IMO It should be up to the cutter, knowing his own skill level, not AGS, to decide how close to the edge he wants to play. He can''t do that if he is not told where the Ideal 0 edge is.

Michael Cowing

I wish it were, but there are just so MANY examples of incompetent cutters, I see them all the time on those rare occassions when I need to look outside the Infinity inventory.

As a sad note, I suspect that many of these cutters who''s goods I reject think of themselves as great cutters. I also think that it is not possible for AGS to post a chart stating exactly where the edge is because that edge is in fact fuzzy with the ability for two stones with the exact same readings on the sarin to fall on either side of the line when actual ray tracing is done.

You and I have been friends for a long time, so please do not read this as an attack, merely the fact that I dissagree with you on this one.

I gave you high praise during my Monday session for being the first one to actually explain to me the fallacy of the nail head being dark because of light leakage, when it was actually the head shadow that made the stone appear dark back that first night we met at the EightStar conference. I fondly remember the late hour that we stayed up to, and appreciate it all these years later as you were the start of my second incarnation as a student of diamond cutting.

Wink

 

[michaelgem]

I gotta love the way everyone (except perhaps RockDoc) is tap dancing around and avoiding my simple request for more knowledge about the range of Ideal 0. Let me repeat for the last time:

I would like to see the charts updated under the exact same original constraints to reflect the current range of Ideal 0 where the combinations such as the 41/35 case are actually an Ideal 0 and not the 1 or 2 they are currently labled.

At the very least this is of academic and educational interest. As Paul said "It is important that we understand them"

Michael Cowing

 

[diagem]

Date: 2/21/2007 4:18:38 PM
Author: RockDoc
RE: Dealers cutting tight symmetrical stones.


What about Eightstar & Whiteflash, Storm?

And how about some of the stones from Hearts on Fire and Blue Nile''g Signature Collection?


Do you think they''re cutting chopped liver?

Paul, GOG''s suppliers, and ISEE2 don''t have a ''lock'' on well executed symmetry.

Correct me if I''m wrong, perhaps I misunderstand your point, but you seem to infer that the above are the ONLY people cutting symmetry well. Not Factual if that is what you meant!

Rockdoc

I have been ''trying'' to follow this thread and found myself rather surprised!!!

Firstly Rockdoc, I must complement your perspective written above... well said and thank you for your objectiveness!!!
Yes I agree with you Rock..., the demand for excellent cut round shapes cant be supplied by just the four named above..., and there are quite few more than just a handfull.

I am still trying to understand the communication between Michael and the PS group..., as someone standing on the sidelines on this one... It doesn''t sound to professional to me..., and again, I am truly surprised.

 

[strmrdr]

Date: 2/21/2007 4:18:38 PM
Author: RockDoc
RE: Dealers cutting tight symmetrical stones.


What about Eightstar & Whiteflash, Storm?

And how about some of the stones from Hearts on Fire and Blue Nile'g Signature Collection?


Do you think they're cutting chopped liver?

Paul, GOG's suppliers, and ISEE2 don't have a 'lock' on well executed symmetry.

Correct me if I'm wrong, perhaps I misunderstand your point, but you seem to infer that the above are the ONLY people cutting symmetry well. Not Factual if that is what you meant!

Rockdoc

8* no clue and don't care... the few iv seen scans from haven't been that tight...
WF ACA line consistant optical symmetry yes, consistently tight nope, and the ACA line is just a small portion of the cutters production.
HOF.. there isnt an hof dealer on ps that I know of.
BN sig. line isnt one supplier but many and there are more than a few total dogs in the bunch.

Tight is the key word there.
If I was listing stones with good looking hearts the list would be longer.

edit to define tight: min. variation in angles of the facets.

 

[JohnQuixote]

Date: 2/21/2007 5:11:23 PM
Author: michaelgem

I gotta love the way everyone (except perhaps RockDoc) is tap dancing around and avoiding my simple request for more knowledge about the range of Ideal 0. Let me repeat for the last time:

I would like to see the charts updated under the exact same original constraints to reflect the current range of Ideal 0 where the combinations such as the 41/35 case are actually an Ideal 0 and not the 1 or 2 they are currently labled.
At the very least this is of academic and educational interest. As Paul said 'It is important that we understand them'

Michael Cowing

Hey Michael,

I don’t presume to be AGS, and may have done a bad job of explaining, but my answer was offered in good faith:I just tried to share an explanation of “why” the guides are conservative the way I understand it from experts I respect at the lab.

If you hope to see the official charts updated maybe your reasoning and request could be made to AGS (?)

 

[diagem]

Date: 2/21/2007 5:41:19 PM
Author: strmrdr

Date: 2/21/2007 4:18:38 PM
Author: RockDoc
RE: Dealers cutting tight symmetrical stones.


What about Eightstar & Whiteflash, Storm?

And how about some of the stones from Hearts on Fire and Blue Nile''g Signature Collection?


Do you think they''re cutting chopped liver?

Paul, GOG''s suppliers, and ISEE2 don''t have a ''lock'' on well executed symmetry.

Correct me if I''m wrong, perhaps I misunderstand your point, but you seem to infer that the above are the ONLY people cutting symmetry well. Not Factual if that is what you meant!

Rockdoc

8* no clue and don''t care... the few iv seen scans from haven''t been that tight...
WF ACA line consistant optical symmetry yes, consistently tight nope, and the ACA line is just a small portion of the cutters production.
HOF.. there isnt an hof dealer on ps that I know of.
BN sig. line isnt one supplier but many and there are more than a few total dogs in the bunch.

Tight is the key word there.
If I was listing stones with good looking hearts the list would be longer.

How do you know PS vendors are not suplied by multiple Diamond Manufacturers/cutters? And are you sure they are not?

 

[strmrdr]

Date: 2/21/2007 5:50:03 PM
Author: DiaGem
How do you know PS vendors are not suplied by multiple Diamond Manufacturers/cutters? And are you sure they are not?

Its common knowledge to anyone who has been here a while.
This is for Rounds only.
WF ACA - dedicated production line at a very large sight holder
WF ES line - multiple cutters.
GOG Classics(cut to specific specs) - 2 main cutters I call em 1 and 2
Rest of GOG rounds 3 other cutters one of whom is the Isee2 branded stone cutter.
Wink - Paul, 8*, with an occasional stone from other cutters in his PGS certed line.
Gary (diamondexpert.com): Paul, others on special order.
NiceIce - don't know anymore.
BN - multiple cutters.
JA - they are now associated with one cutter if the rumors are true but carry other stones.

Rest of em... who cares I dont....

 

[adamasgem]

Date: 2/21/2007 5:41:19 PM
Author: strmrdr
8* no clue and don''t care... the few iv seen scans from haven''t been that tight...

Well we have it on record now.. beids we all know, that up until December, scans on painted breaks from Sarin and OGI were not any good, and probably OGI scans can not handle that class of stone. So if you are basing opinions on flawed data, where we all knew it was flawed as has been widely discussed, then I suggest you refrain from offering opinions...

 

[strmrdr]

Date: 2/21/2007 6:56:26 PM
Author: adamasgem

Date: 2/21/2007 5:41:19 PM
Author: strmrdr
8* no clue and don't care... the few iv seen scans from haven't been that tight...

Well we have it on record now.. beids we all know, that up until December, scans on painted breaks from Sarin and OGI were not any good, and probably OGI scans can not handle that class of stone. So if you are basing opinions on flawed data, where we all knew it was flawed as has been widely discussed, then I suggest you refrain from offering opinions...

I said no clue because I didnt have enough scans to say..
And the ones I did have scans on were helium scans anyway but are older 8* anyway so like I said no clue and dont care....

 

[michaelgem]

Hi John,

Sorry I have not had a chance to get back to you personally.


Re: I don’t presume to be AGS, and may have done a bad job of explaining, but my answer was offered in good faith: I just tried to share an explanation of “why” the guides are conservative the way I understand it from experts I respect at the lab.If you hope to see the official charts updated maybe your reasoning and request could be made to AGS (?)

The explaination you kindly shared is the current AGS position vis-a-vis the grading guideline charts.

In the spirit of openness and a desire to educate I felt that AGS would want to update these charts with the new cut criteria which is slightly more inclusive for the AGS Ideal 0.

As I mentioned, I am especially interested in the AGS position as regards the slightly steep deep angle combinations like Morses 41 and 35. I was suprised when Peter ran those numbers with the guideline constraints and told me it got a zero. Surprised because the chart for a 56 table and 6mm diamond that I was using called it an AGS 2.

I actually did contact Peter with my request. He kindly called me back to say he had seen my posts. If I try to speak for him as to what he had to say, its inevitable that I won't get it right.

So I will simply say that he did not rule out updating the charts, but he is heavily involved right now in more urgent pursuits. Also, anything of this nature would have to be approved up the line.

Ideal regards,

Michael

 

[Serg]

Date: 2/21/2007 7:53:49 PM
Author: michaelgem


Hi John,

Sorry I have not had a chance to get back to you personally.




Re: I don’t presume to be AGS, and may have done a bad job of explaining, but my answer was offered in good faith: I just tried to share an explanation of “why” the guides are conservative the way I understand it from experts I respect at the lab.If you hope to see the official charts updated maybe your reasoning and request could be made to AGS (?)

The explaination you kindly shared is the current AGS position vis-a-vis the grading guideline charts.

In the spirit of openness and a desire to educate I felt that AGS would want to update these charts with the new cut criteria which is slightly more inclusive for the AGS Ideal 0.

As I mentioned, I am especially interested in the AGS position as regards the slightly steep deep angle combinations like Morses 41 and 35. I was suprised when Peter ran those numbers with the guideline constraints and told me it got a zero. Surprised because the chart for a 56 table and 6mm diamond that I was using called it an AGS 2.

I actually did contact Peter with my request. He kindly called me back to say he had seen my posts. If I try to speak for him as to what he had to say, its inevitable that I won't get it right.

So I will simply say that he did not rule out updating the charts, but he is heavily involved right now in more urgent pursuits. Also, anything of this nature would have to be approved up the line.

Ideal regards,

Michael

Hi Michael,

AGS published several type guideline charts and spread data in txt( or Excel) format.
Grading rules from these charts are quite different. We try compare GIA and AGS charts. But AGS have two type charts( Pavilion-Crown, Crown-Pavilion. AGS changed direction axis’s in one time) Results are quit different

See below link

http://oct.gemology.ru/oct/mss/

I want receive explanation from ASG too/

 

[Serg]

shortly:

AGS 2004-2005 chart

AGS2006 chart

Could anybody explain it or correct? Do you have other data for T 57?
These charts for girdle 3% and 3.5% , But I do not think it is main reason.
Could anybody publish similar data for exactly one girdle and Table with angle step 0.2 degree?

 

[Serg]

On one AGS chart P41Cr35T57 has grade AGS 3, P40.6Cr36T57 has grade AGS 0

On other AGS chart P41Cr35T57 has grade AGS 0, P40.6Cr36T57 has grade AGS 1

just Conservative policy can not explain it

 

[strmrdr]

Date: 2/22/2007 7:42:11 AM
Author: Serg

On one AGS chart P41Cr35T57 has grade AGS 3, P40.6Cr36T57 has grade AGS 0

On other AGS chart P41Cr35T57 has grade AGS 0, P40.6Cr36T57 has grade AGS 1

just Conservative policy can not explain it

My theory is that you have to go back to the way the grade is calculated.
Its based on virtual ASET 30 and 40 and virtual dispersion scope, with a spreed penalty.
Any stone regardless of the proportions that gets a certain grade on those tests get a 0 or a 1 or a 2 or what ever...
I think that once they had the software and start running combos that a wider range of cuts passed the test than was initially thought and it moved the range a little.

If one thinks about it and looks at the ASET/Dispersion chart that Wink calls the DNA of diamond cutting you will see several zones of reds and yellows that aren''t in the official proportion range that could get AGS0 based on the virtual scopes if the spread makes the cut off.

We are used to thinking of diamond performance grading based on proportions and the AGS grade isn''t directly based on them is where a lot of the confusion is coming from I think.

Kewl stuff

 

[Serg]

re:We are used to thinking of diamond performance grading based on proportions and the AGS grade isn''t directly based on them is where a lot of the confusion is coming from I think.

I do not believe what AGS changed just charts for cutters. If they changed charts they probably changed Grading software or rules firstly.
It is mean what one stone could receive AGS 3 in 2005 and AGS0 in 2006.
Without any explanation and information for consumers, cutters,..
What is value such cut grade?

 

[michaelgem]

Date: 2/22/2007 7:42:11 AM
Author: Serg

On one AGS chart P41Cr35T57 has grade AGS 3, P40.6Cr36T57 has grade AGS 0

On other AGS chart P41Cr35T57 has grade AGS 0, P40.6Cr36T57 has grade AGS 1

just Conservative policy can not explain it

Thank you, Sergey.

You have looked into this more deeply than I have, and perhaps than anyone has.

From a research, learning and educational perspective I would like to know the current thinking and position of the AGS as to the extent of the Ideal 0 range. It seems like an update and redo of these original guideline charts would be the easiest way to accomplish this.

Perhaps if enough of us express a desire for this to happen, Peter will be able to raise its priority and get the approval of his management.

Ideal regards,

Michael Cowing

 

[RockDoc]

I just don''t see how charts can be used for grading. I think it is irresponsible to issue a grade just based on the numbers. There are far too many other factors that can affect light performance in a stone.

How the crystal was oriented when being cut, I believe can have a significant affect on the resultant light performance when turned to save weight.

I have also observed light performance differences relevant to TRANSPARENCY of the stone. I am surprised that this is almost never mentioned in the grading of light performance/cut grading. This is a characteristic that charts or scans can''t discern. It can only be observed and "rated" with highly experienced and trained human eyes. Currently there is no standard of transparency that the gemological community can rely on by using master stone examples. It''s just a judgment call made by those who take this into consideration when visually examining the stone. One also needs to question as what is acceptable and what isn''t.

I''m not even sure if cutters can "control" the affect. But I have certainly seen a difference in various diamonds, where some have incredibly clear transparency and other don''t quite display this. Unfortunately, no chart, set of proportions, or ray tracing can analyze this characteristic. I think that whatever happens, happens and no one really knows the extent of the affect, until the facteting and polishing is completed. I do suspect, it is not taken into consideration, by the majority of graders, cutters and labs.

We''d all like to have a simplistic way to get to the "edge" of what constitutes the best or the next best grading for cut, but using just a chart to determine this, is a bit lacking in its scope of accuracy.

Rockdoc