Discuss Review of GIA Foundation article posted in the Journal

[Garry H (Cut Nut)]

Edit - try this link http://journal.pricescope.com/Categories/3/Diamond-Grading.aspx published in the Fall Gems & Gemoology 2004 can be found at that link in the Pricescope Journal catagory.
I would be happy to discuss the article here on the Forum on this thread rather than on the various threads all over the board.

 

[DiamondExpert]

Garry - I couldn''t get the link to work.

 

[Garry H (Cut Nut)]

Sorry try this one
http://journal.pricescope.com/Categories/3/Diamond-Grading.aspx

 

[Fleimstaler]

Hi Garry,

thanks for indicating the link. I went through your article and is really impressive I have not read it as it is too long. I will do it as soon as I can.
Thanks and rgds.

Fleimstaler

 

[perry]

It seems to me that GIA again focuses on supplying the least usefull information of the major labs. So what is new about that.

Of course, since there main customer is the diamond cutter - I suppose that the diamond cutters of poor cut diamonds will be pleased.

At what point will a GIA cert be considered almost useless by the buying public.

Wait, you allready need sarin or mega reports with a GIA cert just to get the angle information.

Perry

 

[strmrdr]

Date: 1/11/2005 6:44:55 AM
Author: perry
It seems to me that GIA again focuses on supplying the least usefull information of the major labs. So what is new about that.


Of course, since there main customer is the diamond cutter - I suppose that the diamond cutters of poor cut diamonds will be pleased.


At what point will a GIA cert be considered almost useless by the buying public.


Wait, you allready need sarin or mega reports with a GIA cert just to get the angle information.


Perry

Yep thats my take on it too.
Gia is proving once again that they are bought and paid for by the industry not consumers.

 

[valeria101]

The price forecasting at the end of the article prices lab paper by it’s weight in diamonds. Now, that’s a deal, no ? Not to mention that cut is entirely made not born like carat, color and clarity presumably are.

At a first read, a couple of its from the article proved particularly useful to navigate the tangle. Here they are, starting with an eye opening question:

How fair is the system ? Well…
“I question the validity of this grade that would apply to the worst 1% of certified diamonds based on a survey conducted on Rapnet on 11/19/2004. There were only 441 plus 1.00ct rounds with depth % greater than 69% listed out of approximately 40,000 round stones searched by the same criteria. Surely the lowest grade in a 5 grade system should be set to reflect around 10 to 20% of the goods in the market?”
Can buyers possibly see more in their diamonds than GIA does ? Sure so….
“If this survey had involved consumers actually purchasing diamonds, spread and apparent size would [but ain’t n.r.] have been a very important factor in the grade setting of this and some other stones.”
So what is a shopper to do with these ?
A readable companion to the GIA lab report sounds like a good idea, doesn’t it ?
User friendly as is, this article is no user guide. Is GIA preparing one? Is it too early? A certain bit of the article sounds like a particularly good start. A certain table (on page 10) makes a rare invitation to ponder if and how those grades show anywhere but on the price tag. Thank you ! Finally a way to read through those intricacies at a glance. “At a glance” is way more democratic than a thick tome.
By all means, something that takes 5 seconds to read and 10 minutes to understand has a better chance to urge an open minded view over those precious grades.

For starters, it would be interesting to add one more line on the table for the cut grades and collect Pricescope wisdom into it. Something like this:

 

[Regular Guy]

Garry,

Just a few thoughts after a couple of passes..lots of calculus there, despite your having truncated a larger piece of work....

Is part of the problem that GIA''s system for good vs not so good, is that all of the options are pretty eliptical, vs. being circular or even boxes going up & down? Guess I''m saying that a) all the options track the red area on the HCA chart, and b) two of the 3 ideal scopes in each option looks reasonble/redish to me, with a very untrained eye.... Alternately, maybe you really never get some bad options from that point of view, with the basic shape of all diamonds tending towards pretty good.

The section at the end on pricing...I also found that very intersting...and I know I''ve read that part before.

Finally...seems like your point on the chart itself, Garry, that Ana pulls out...is that you''ve simplified those "so-called" outliers to just those items, leaving it clear to show proportions is really all you have left that are the substantive elements to speak to light behavior, and it''s not necessarily smoke & mirrors after all.

 

[Garry H (Cut Nut)]

You make some good points Dave and Ana.

Ira could you re-write your comments - they are a little hard to follow.

Have any of you read the GIA article? I knowFlem has.

I am happy to take suggestions to add to the article also.

 

[Dancing Fire]

GIA should forget about putting a cut grade on their cert ,just put all the specs and let the consumer decide by using their eyes,HCA,AGA,IS,B-scope,Isee2 etc,etc...

 

[perry]

Yes, Garry. I did read the article.

While I think that there is a general trend there to represent somthing of a cut grade, and the Idea is somewhat laudable. I found that what was being proposed was a lot short of what I think, as an engineer, could have been done. Hence, my previuos comment.

Do you have, or know of, a similar article about what AGS is proposing?

Perry

 

[lostdog]

Very interesting assessment, Garry. Thanks for sharing it (and to Leonid).

A few notes, just reactions from my limited perspective:

From page 11:
"The findings of this GIA study, and other studies and approaches to cut grading, will fundamentally change industry expectations. If part of the purpose of this GIA article is to change those preconceptions to match the findings of human observers and the realities of the laws of physics, why be considerate of preconceived trade customs and opinions? As Paul Slegers says, we should not be led by logic dictated by adages like “my child is beautiful”. This would lead to a lost opportunity to take full advantage of the laws of nature to maximise both the beauty and the yield on each and every one of those “finely crystallized carbon” creations.

Paul also notes that trade observers are educated in a certain way of looking, judging and thinking. No matter how ‘blind’ you make their observations by not giving them any parameters before judging, they can identify certain parameters and they may inevitably be influenced in their observational judgements. "

While I think I know what you are getting at, that the stones were being judged relative to the exisiting concept of ideal, but on some level changing the preconceptions of those involved in the study with the results of the same study sounds a bit circular in logic from the outset.

That said, that some people with "trade eyes" might be looking at a stone for isolated characterisitics and biasing the grading response without really looking at the visual performance seems to be an important failing. Is there a breakout in the study of consumer preferences compared to professionals?

There''s still a lurking question of who the beholder of the beauty is, i.e. judging beauty presupposes some standard.

From page 12:
"Secondly, the GIA article mentioned that diamonds that exhibited excellent symmetry with Ideal-Scope or Hearts and Arrows viewers were not rated any higher by observers than those with lessor patterns. I suspect that their study only focused on diamonds within very good proportions, and in this respect, Peter Yantzer and I have never subscribed to the idea that Hearts and Arrows diamonds offer any better appearance to the naked eye than well cut diamonds with small symmetry deviations. Had GIA tested diamonds with the ideal-scope with the purpose that it is designed to be used for, rather than simply as a gauge of symmetry, I feel they would have discovered benefits form its usage and weaknesses in their current symmetry grading method. "

Maybe explicitly stating "light leakage" versus optical symmetry would be clearer?

I still wonder that symmetry isn''t properly accounted for, as you point out.

From page 12:
"For instance diamonds that have painted or built up upper girdle facets like EightStar diamonds® were said to show “little..."

An honest question, do EightStars have painted facets?


- - -

Cat 5 does appear there only make sure that Cat 4 is better than something.

- - -

Maybe this belongs in a separate topic, but what would be the ultimate ultimate methodology and grading system?

 

[Regular Guy]

OK, in for a penny, in for a pound.

Since I have no proper reputation to sully, here I go. Thanks in advance for forgiving big mistakes. I find the Pricescope info hangs together logically in a way that I feel like usually, with one thing pointing in a straight line to another, one idea flows pretty well to the next, and I am motivated to participate. In the case of this response…I’m more going out on a limb.

In the case of this study you''ve reacted to, Garry, no, I''ve not read the original. Hard enough time skimming yours. Still, some reactions, and questions, I''ll try to re-state here.

Regarding my last point above, and generally...your review is very "context dependent" upon the original piece. So, it is a review...naturally. You say right at the beginning: "(the categories) may not be the basis of the final grades. It seems their foundation is incomplete which means that this analysis of it must also be incomplete." Relatedly, on your screen 10, where you present the chart of reported effects to light performance, you introduce it with this comment: "The GIA study noted during the observational survey that factors other than proportions played a role in diamond beauty. This table attempts to simplify those observations." My hunch is simply that your intention in providing the details of the chart is to shoot down the paper tiger and intended suggestion that proportion data is not substantially sufficient to provide for cut grades. The items in the chart do not seem substantive, and I was betting you were just trying to draw the items out, putting them in black & white. Wrong?

My point on your comments on pricing and cut were just that...good stuff. I recall reading similar or identical comments on this board before, presume they were for you, and bear repeating.

Finally...a "second" reaction to your piece, and the first point I tried to make above...really, this point is embedded in some fundamental questions I have about HCA and diamond cut grading generally. First of all, allow my complete relative ignorance about crown & pavilion angle actual patterning in the real world. Of course, without this knowledge, setting up schemes to measure them could be sharply criticized. And yet, let''s point out that your fundamental typology of BIC, TIC and FIC as describing the spectrum of ideal cuts has as one of them a class (FIC) that you describe as occurring as about 1 in 2000, wasn''t it? So...basic questions:

1) Given the classic graphical display represented coincident with the HCA report, where you get the big red pathway going from “Northwest to Southeast,” i.e., upper left to lower right, I suppose that your frequent cry to suggest the range of ideal cuts can be expanded is consistent with this broader big red valley…given this broad swath of red…why the more narrow option for AGS0 in their newer system…why not a bigger spectrum. Also, and likewise…to what extent does that big red area map onto your own system of categorizing of 0 – 2…maybe the match is not that great.

2) Generally, if we allow that the big red area on the HCA presentation suggests good performance…and I do know that upper left portions and lower right portions do stake out the BIC and FIC typology…then it would seem a mistake to have poorer cut diamonds follow the track of this big red area, which is what at least GIA 1 – 3 seems to do. So, maybe this doesn’t make any sense…and I’ll qualify it by pointing out that in the last month, people on the Pricescope board have queried about diamonds that are very clearly in the outlying blue areas of the chart at the upper right, suggesting some actual diamonds under consideration do exist out there…but my question is basically…wouldn’t it make more sense for poorer cut diamonds to follow a path perpendicular to the big red area on the HCA chart..or does this make no sense…perhaps representing no, or not many actual diamonds. I’m intending to attach below a highly primitive mockup of us just such a chart. And that’s my 2 cents for today. Your indulgence is greatly appreciated.

 

[valeria101]

About the outliers...

Well, of course one needs this particular refference to define them as such. Isn't this what you mean, Ira ?

I did give this a thought too - plotting on a chart comes faster than knee-jerk by now

. Clearly (IMO) some strong assumptions are needed to draw those ovals as they are. The article states them:

"In the chart shown here, an interpretation is made of some ranges of proportions given by the GIA based on my assumption that the GIA would concur with previous work done by MSU, Bruce Harding and Jasper Paulsen’s re-interpreted Tolkowsky calculations."

However, the authors appear to acknowledge that GIA's theory falls somewhat beyond these assumptions, since the paragraph continues:

" But it should be noted that three of the 15 example stones fall outside these oval predictions."

GIA does not publicize their assumptions as openly as Garry did for his system and MSU does... hence I am not totally safe bringing these assumptions up. Surely, I am not as confortable with the theory as the authors either. From where I stand, the article is a critique of GIA results based on HCA assumptions. This may not have been totally fair methodology if GIA left their assumptions in the open. Since this is not the case, why not. As is, Garry's chart does show how well HCA predicts GIA's grades and the fit is quite impressive.

For statistic sake, three outliers would not be worth a footnote - error is expected. For diamond grading error doesn't seem acceptable at all - even when everyone knows it's there ! Giving the outcasts a thought, two alternative arguments come to mind.

One involves minor facets (and this GIA takes into account). Since Jonathan brought this up ages ago, I hope he could chime in. It seems fair to put two together: #1. GIA's associating minor facet complements to crow&pavilion proportions, with #2. Jonathan's demonstration that minor facets make sensible differences even in the narrow class of ideal proportions and H&A symmetry. It comes naturally to conclude that minors do have the potential to relax the crown/pavilion determination of optics in general. Of course, my understanding of all this is at best amaterish.

The other relates to the HCA chart - Garry did note outliers to the crown/pavilion relationship anyway: what's the green kink that comes close to the darn outliers? That can't be motivated by the crown/pavilion angle trade off, no ? What is it all about ? Perhaps the answer to that would clarify GIA's concept as well.

That until now ideal standards (by HCA, EGL, HRD, AGS - as much as I understand them from public information) considered crown and pavilion proportions only is no fault of precission, I think. Parcimony is a merit for any model, not just diamond cut metrics. Adding minor facets to the mix called for better then Sarin and that might not have appeared to be worth the trouble. If GIA does put his weight behind the minors, perhas it will be worth going to the next level of complexity.

HCA does not take minor facets into consideration. Perhaps HCA 2.0 will Garry ?


Along the same line of argument opened above, the HCA set of variables may need to expand to meet GIA's. The current HCA version does not take minors into acount by construction. If version 2.0 will, then the shape of the change is not unpredictable: it would be on a vector opposite the existing support - right towards the respective outliers, that is. Not that following GIA is a noble goal in itself.

 

[Garry H (Cut Nut)]

Date: 1/12/2005 2:45:52 AM
Author: lostdog
Re Paul from Antwerps comments about the trade observers being "preconditioned"
While I think I know what you are getting at, that the stones were being judged relative to the exisiting concept of ideal, but on some level changing the preconceptions of those involved in the study with the results of the same study sounds a bit circular in logic from the outset.

That said, that some people with ''trade eyes'' might be looking at a stone for isolated characterisitics and biasing the grading response without really looking at the visual performance seems to be an important failing. Is there a breakout in the study of consumer preferences compared to professionals?

There''s still a lurking question of who the beholder of the beauty is, i.e. judging beauty presupposes some standard.

Here is a link to one of my most ardent hate club fan leaders discovery of a diamond that in their opinion proved that the numbers are a bad predictor of diamond beauty. Now I agree that such a stone would, by its numbers, look very attractive - but the trade observers would easily have picked it as "wierd". http://www.diamondtalk.com/forums/showthread.php?t=54913

I still wonder that symmetry isn''t properly accounted for, as you point out. Yes - it is a problem that GIAmis aware of, but solving such a problem when you have 50 years of baggage is not so easy. As Einstein said "You can not solve problems with the same thinking that created it". GIA have made attempts to bring people from outside the organisation and the industry to work on this project - but even that is not easy to pull off.

From page 12:
''For instance diamonds that have painted or built up upper girdle facets like EightStar diamonds® were said to show “little...''

An honest question, do EightStars have painted facets? Yes, of course they do

- - -

Cat 5 does appear there only make sure that Cat 4 is better than something.

- - -

Maybe this belongs in a separate topic, but what would be the ultimate ultimate methodology and grading system?
scan the diamond and build an excellent 3D model, then use physics and software to judge the diamonds beauty based on a range of basic light responses calibrated by humans. The greater benefit of such a system is that it can then be used to reverse engineer the design of truly beautiful diamonds - it can even lead to freestyle designs and one off pieces that follow the outline of the rough diamone yet still produse a beautiful diamond. Sergey Sivovolenko who designed DiamCalc and the worlds most advanced Sarin type scanners is the world leader in this field.

 

[Garry H (Cut Nut)]

Date: 1/12/2005 3:10:26 AM
Author: Regular Guy
In the case of this study you''ve reacted to, Garry, no, I''ve not read the original. Hard enough time skimming yours. Still, some reactions, and questions, I''ll try to re-state here.
Ira you are an excellent contributor. I asked who had read the article because I want to know that people are not only responding to my biased view of the world.
Perry you said you had read the article - did you mean mine, or th GIA''s - that is what i meant

''The GIA study noted during the observational survey that factors other than proportions played a role in diamond beauty. This table attempts to simplify those observations.'' My hunch is simply that your intention in providing the details of the chart is to shoot down the paper tiger and intended suggestion that proportion data is not substantially sufficient to provide for cut grades. The items in the chart do not seem substantive, and I was betting you were just trying to draw the items out, putting them in black & white. Wrong? Wrong - if you read over many of my posts in the past few months you will find references where I quote those opinions because by and large i agree with them (aside from the issue that they have a fallable symmetry grading system).

My point on your comments on pricing and cut were just that...good stuff. I recall reading similar or identical comments on this board before, presume they were for you, and bear repeating. Yes but Paul told me not to put them in because it is purely my opinion and it is not a "review" of the GIA paper. he is right of course (he is a very wise person) but i could not resist because i am a weak fool

Finally...a ''second'' reaction to your piece, and the first point I tried to make above...really, this point is embedded in some fundamental questions I have about HCA and diamond cut grading generally. First of all, allow my complete relative ignorance about crown & pavilion angle actual patterning in the real world. Of course, without this knowledge, setting up schemes to measure them could be sharply criticized. And yet, let''s point out that your fundamental typology of BIC, TIC and FIC as describing the spectrum of ideal cuts has as one of them a class (FIC) that you describe as occurring as about 1 in 2000, wasn''t it? So...basic questions:

1) Given the classic graphical display represented coincident with the HCA report, where you get the big red pathway going from “Northwest to Southeast,” i.e., upper left to lower right, I suppose that your frequent cry to suggest the range of ideal cuts can be expanded is consistent with this broader big red valley…given this broad swath of red…why the more narrow option for AGS0 in their newer system…why not a bigger spectrum. Also, and likewise…to what extent does that big red area map onto your own system of categorizing of 0 – 2…maybe the match is not that great.
Firstly, the big red area is less than 2 on HCA. Secondly if diamond cutters were not pealised in the market by that vicious "crown angle greater than 36 degrees" then they would cut more of those stones - there is plenty of that type of rough and the yeild is great. thirdly AGS have a 10 inch viewing distance which I think is madness - Peter agrees that diamonds that look great at 14 inches make fabulous pendant and earring stones. Not everyone can or wants to examine the beauty of a diamond from 10 inches.

2) Generally, if we allow that the big red area on the HCA presentation suggests good performance…and I do know that upper left portions and lower right portions do stake out the BIC and FIC typology…then it would seem a mistake to have poorer cut diamonds follow the track of this big red area, which is what at least GIA 1 – 3 seems to do. So, maybe this doesn’t make any sense…and I’ll qualify it by pointing out that in the last month, people on the Pricescope board have queried about diamonds that are very clearly in the outlying blue areas of the chart at the upper right, suggesting some actual diamonds under consideration do exist out there…but my question is basically…wouldn’t it make more sense for poorer cut diamonds to follow a path perpendicular to the big red area on the HCA chart..or does this make no sense…perhaps representing no, or not many actual diamonds. I’m intending to attach below a highly primitive mockup of us just such a chart. And that’s my 2 cents for today. Your indulgence is greatly appreciated. I do not completely follow this last bit - but i think your questions may be answered?

 

[Garry H (Cut Nut)]

Date: 1/12/2005 3:31:47 AM
Author: valeria101
About the outliers...

GIA does not publicize their assumptions as openly as Garry did for his system and MSU does... hence I am not totally safe bringing these assumptions up. Surely, I am not as confortable with the theory as the authors either. From where I stand, the article is a critique of GIA results based on HCA assumptions. This may not have been totally fair methodology if GIA left their assumptions in the open. Since this is not the case, why not. As is, Garry''s chart does show how well HCA predicts GIA''s grades and the fit is quite impressive. Ana remeber that AGS have also broadly agreed with the other proportion ranges - so GIA is the one with the outlyers - but Sergey provided an ETAS (his new bbay you will be seeing more of later) map that shows the GIA stone has loads of bright firey spots - i have attached the photo - someone might like to find which page the discussion is on (please).

For statistic sake, three outliers would not be worth a footnote - error is expected. For diamond grading error doesn''t seem acceptable at all - I have not said that stone is an error - infact when you look on the HCA chart you see a funny green finger in the sea of blue to the upper right center area. I liked those stones even though logic told me not to like them. even when everyone knows it''s there ! Giving the outcasts a thought, two alternative arguments come to mind.

One involves minor facets (and this GIA takes into account). Since Jonathan brought this up ages ago, I hope he could chime in. It seems fair to put two together: #1. GIA''s associating minor facet complements to crow&pavilion proportions, with #2. Jonathan''s demonstration that minor facets make sensible differences even in the narrow class of ideal proportions and H&A symmetry. It comes naturally to conclude that minors do have the potential to relax the crown/pavilion determination of optics in general. Of course, my understanding of all this is at best amaterish. 1. Here is an attack from me clearly made against GIA - GIA bring up minor facets mainly as a political attack on AGS. have no doubt - if I mean it I will say it - so do not go looking for vield and hidden meaning - I say what I mean and mean what i say. 2. I never said minor facets were not important - I said trying to quantify them with HCA would be silly (take that as a GIA critique too if you like). Rhino overstates them as part of a belief or a commercial strategy - I see less than 5% of otherwise nice stones with small minor facet irritations - and almost never really bad e.g.''s.

HCA does not take minor facets into consideration. Perhaps HCA 2.0 will Garry ? HCAPro would be next - it would be for manufacturers to make production easier and less risky. Manufacturers who are interested already know or want to know about how to make the minor facets right and it is not rocket science - here is an email we got this week - We would like to know what is the importance of HALVES and STARS in a diamond.What are "percentage" required for diamonds of different TOTAL HEIGHT.We would like your advice on that and if any person whose advice could be taken or any websites which can be searched on.



Along the same line of argument opened above, the HCA set of variables may need to expand to meet GIA''s. The current HCA version does not take minors into acount by construction. If version 2.0 will, then the shape of the change is not unpredictable: it would be on a vector opposite the existing support - right towards the respective outliers, that is. Not that following GIA is a noble goal in itself.

 

[valeria101]

Date: 1/12/2005 6:34:21 AM
Author: Garry H (Cut Nut)

(1) Sergey provided an ETAS map (his new bbay you will be seeing more of later)

(2) when you look on the HCA chart you see a funny green finger in the sea of blue to the upper right center area. I liked those stones even though logic told me not to like them.

(3) I never said minor facets were not important - I said trying to quantify them with HCA would be silly (take that as a GIA critique too if you like). ... I see less than 5% of otherwise nice stones with small minor facet irritations - and almost never really bad e.g.'s.

Thank you for the reply

(1) The ETAS definitely stands out (page 7) - something that spectacular cannot pass quietely ! And there are not too many metrics for observed fire anyway. Only Eight Star did something of the sort, no ?

(2) Noticed the "green finger" too (the "vector" argment above) - just didn't know that is an empirical adition to the HCA logic. I think you did mention this before, but I smehow suspected there is more complicated theory behind the color spill. GIA's outliers appeared to reinforce that thought. Any ideas what the explanation for the green finger might be ? "Thought the same would make HCA sense of GIA's choices after all.

(3) Minor facets... well, I have no reason to disagree that at some point this added cut grading factor is splitting a very, very thin hair (the starin of H&A ideals that is). But, is it possible to improve the looks of a stone with so-so crown&pavilion match by modifying the minors ? Jonatahan's page does not deal with this of course. It seemes that GIA does. Wrong ?
Picture comming up.

 

[valeria101]

Looking at those Iscope examples it may seem that the GIA grades are more lenient with lickeage than the HCA is.
Is this bad ? A bit back, a chart quantifying Iscope reds came up making an excuse for lighter reds too, although not as much excuse as GIA scores suggest.

 

[strmrdr]

To give the other side of the minor facet story.
The more I study the diamond cut issue and talk to Rhino, Brian and John the more important I think the minor facets are.
They disagree a little (less than they think) on where the ideal range is for them but all 3 think its one of the more important aspects of cutting well performing diamonds.

If they overstate them answer me this:
Take 5 diamonds with the exact same crown and pavilion angles, girdle rating, and diameter.
They get the exact same hca score, ags score, and gia cut score.

Eight star
new line aca
classic aca
GOG classic profile
venus by infinity

The cut grades tell you these diamonds are the same but due to differences in the minor facets they prefere and girdle treatments they would look noticeable different from one another under almost all light conditions.

further:
Garry,
Looking at page 2 of your review you state:

"This is enhanced by short lower girdle facets (LG’s)."

on another diamond.
"Shorter LG’s could improve the stone."

So I guess im confused on what your real stand is on minor facets?
Mainly LG''s.

 

[valeria101]

Hm... I hope I didn't open the proverbial can. If so, feel free to close everyone. I hardly know what I am talking about here, and it's all you guys (Garry and Jonathan mostly) teach anyway.

It just so happened that two examples where GIA and HCA parted ways happened to have the extreme minor facet % of the small sample. If the numbers weren't there I could have never add a post to this technical thread

 

[Garry H (Cut Nut)]

Ana the leakage in the worst example of Cat 2 - RD07 2.2 is not total leakage - I have shown it here in this DiamCalc ray trace entering in the bad leakage area to the left of the center of the stone. This small amount of light return would very likely show as fire because of the lack of light return from that region in the stone. Also if such a stone were set so some light could get in its pavilion it would be very firey.

Re the shallow stone examples and your idea about the minor facets - remeber they have good spreads, so HCA gives no spread penalty like it would for say a Tolkowsky stone - if you took away that spread factor then their 4ish scores are worse than they seem. They are simply flat stones - but they would have more market appeal because they look big for the money.

 

[Garry H (Cut Nut)]

Date: 1/12/2005 8:47:14 AM
Author: strmrdr
To give the other side of the minor facet story.
The more I study the diamond cut issue and talk to Rhino, Brian and John the more important I think the minor facets are.
They disagree a little (less than they think) on where the ideal range is for them but all 3 think its one of the more important aspects of cutting well performing diamonds.

If they overstate them answer me this:
Take 5 diamonds with the exact same crown and pavilion angles, girdle rating, and diameter.
They get the exact same hca score, ags score, and gia cut score.

Eight star
new line aca
classic aca
GOG classic profile
venus by infinity

The cut grades tell you these diamonds are the same but due to differences in the minor facets they prefere and girdle treatments they would look noticeable different from one another under almost all light conditions.
Looking different does not mean looking bad, or better or worse from a grading point of view Storm. For instance I give HCA under 2 to diamonds with crown angles of 30 and also 37. They look completely different to each other - but they each have appeal to most people and some have more appeal to different types of people. I have no beef with the anal approach of Brian and Rhino et al; but they are working in a very rarified area of diamond cut and it is not GIA''s or my intent that this be a standard expectation. Even Peter Yantzer from AGS, who might like to buy a super ideal cut for himself because he can truly appreciate the skill and precision that goes into making such a product - does not seek to set such standards for normal commercial grading by providing extra recognition for H&A"s pattern grades. If you ask him why, he say''s that there is insufficient evidence to show that a diamond with very nice symmetry is less beautiful than one with perfect symmetry.
further:
Garry,
Looking at page 2 of your review you state:

''This is enhanced by short lower girdle facets (LG’s).'' You misunderstand me Storm - I have never said that minor facets are unimportant - I said it was too complex to add into HCA - who can even get accurate measurements? And I said that the frequency of problems caused by minor facets is small - you might note that all those who claim they are vitally important have an axe to grind. Take the specialist vendors, GIA vs AGS and certain appraiser who hates HCA and uses the minor facet attack to get business.

on another diamond.
''Shorter LG’s could improve the stone.''

So I guess im confused on what your real stand is on minor facets?
Mainly LG''s.

 

[valeria101]

Date: 1/12/2005 4:51:17 PM
Author: Garry H (Cut Nut)

They are simply flat stones - but they would have more market appeal because they look big for the money.

I see... honestly, I didn't get to split the HCA scores.

One of the GIA 2 comes with 90% or so lower girdle facets - definitely reminded me of some branded rounds sporting super long lower girdles and large tables as their winning solution.

From the dozen examples, it seems that the good ol' crown/pavilion tradeoff remains the safet bet, with GIA's first two classes a reasonably relaible sourse of not-quite-ideal candidates for inspection. This, at least until cut recipes get tweaked to just make the new set of grades, I guess. Wrong ?

 

[JohnQuixote]

I will wait until final polish to judge the GIA system, but I agree with Dave that the fact that it’s being established is a step forward.

 

[JohnQuixote]

Ok. Some cursory comments about the GH review:

1. It should not be surprising that the 5th grade (assume it will be called “poor”) will not be seen on many reports. After all, how often do we see graded diamonds with poor symmetry or polish? Having a “throwaway” grade is to promote value for grades 1-4.

2. Fluoro is prominent in the review as having “No effect on apparent brightness and fire.” Will this influence an adjustment to reduce or eliminate discounts for fluorescent goods?

3. The barrage of new information could, for a time, make existing tools even smaller pieces of a larger overall puzzle. For a RB diamond someone wishing to scrutinize to the “nth” degree could seek out…

Carat weight
Color, Clarity, Sym, Polish, Girdle, Culet (and the lab that did the grading)
AGS Cut Grade
GIA Cut Grade
AGA Cut Grade
Standard Sarin proportions
Minor facet Sarin proportions
Ideal Scope Image
Hearts & Arrows Image
HCA prediction
Virtual Modeling prediction
Ray Tracing, Angular Spectrum evaluation
BrillianceScope / Isee2 / Imagem prediction

That’s a lot of information.

Garry, thank you for the obvious time and effort you put into giving your perspective.

 

[JohnQuixote]

Date: 1/11/2005 7:45

6 PM
Author: Dancing Fire
GIA should forget about putting a cut grade on their cert ,just put all the specs and let the consumer decide by using their eyes,HCA,AGA,IS,B-scope,Isee2 etc,etc...

DF, with a grading system already in the mix it''s not that simple.

This is the problem inherent with a major player trying to adopt a system where a precedent has already been set. AGS has been grading cut for almost a decade.

It is a no-win scenario for GIA, because if they just put the proportions on the report people will still seek and refer to the corresponding AGS grade as the standard. Alternately, with establishing a new system there are going to be comparisons to the existing one and critics will be rife. The simple fact is that AGS set the curve. There is something to be said for "getting there first," thus the no-win in many ways for GIA right now. Give it time.

Again, I think we can reserve final judgement ''til we see what GIA does and how it differs from the old and the new AGS. I think the fact that GIA is taking the plunge with grading of cut is a major step forward. Savvy consumers will still have the "tools and toys" to put together pieces of their own puzzle as they wish.

 

[JohnQuixote]

Date: 1/11/2005 8:56:33 PM
Author: perry

Do you have, or know of, a similar article about what AGS is proposing?

Perry

This piques my curiosity: Though it appears that AGS and GIA will vary in their final offerings it will be interesting to note what range of proportions fall in any overlapping area at the top of both systems... This will be an interesting "meaty" range. Names for it, anyone?

 

[JohnQuixote]

Date: 1/12/2005 7

2:22 AM
Author: valeria101

(3) Minor facets... well, I have no reason to disagree that at some point this added cut grading factor is splitting a very, very thin hair (the starin of H&A ideals that is). But, is it possible to improve the looks of a stone with so-so crown&pavilion match by modifying the minors ? Jonatahan''s page does not deal with this of course. It seemes that GIA does. Wrong ?

Ana, I was intrigued by this as well. The hair-splitting I''ve done regarding minor facets is mostly relative to stones with a tight set of major proportions (already is a known performer), though I have interest in unilateral applications. Rhino and I were on the verge of starting a discourse on this very topic when we both went on vacation for a week.

I was very interested in GIA''s apparent opinions here, though Garry''s take is that they include minors for political reasons (one-up AGS). Looks like time to play with DiamCalc, yes?

 

[JohnQuixote]

Date: 1/12/2005 8:47:14 AM
Author: strmrdr
To give the other side of the minor facet story.
The more I study the diamond cut issue and talk to Rhino, Brian and John the more important I think the minor facets are.
They disagree a little (less than they think) on where the ideal range is for them but all 3 think its one of the more important aspects of cutting well performing diamonds.

If they overstate them answer me this:
Take 5 diamonds with the exact same crown and pavilion angles, girdle rating, and diameter.
They get the exact same hca score, ags score, and gia cut score.

Eight star
new line aca
classic aca
GOG classic profile
venus by infinity

The cut grades tell you these diamonds are the same but due to differences in the minor facets they prefere and girdle treatments they would look noticeable different from one another under almost all light conditions.

further:
Garry,
Looking at page 2 of your review you state:

'This is enhanced by short lower girdle facets (LG’s).'

on another diamond.
'Shorter LG’s could improve the stone.'

So I guess im confused on what your real stand is on minor facets?
Mainly LG's.

Garry characterizes these examples as a rarified area of diamond cut. It’s true. The tolerances for “A Cut Above” major proportions are already tight, just as they are for 8*, Venus and H&A endorsed by Rhino and Robin&Todd. Within this realm of already-tight proportions the minutiae we insist on for minor facet construction does not influence the degree of beauty so much as the character of the beauty. We call it fine-tuning the visual balance. The effects are noticeable to the most discerning, but the stones are all beautiful and noting differences would be splitting-hairs in the world of normal commercial grading.

Of course Strm, you are correct that those of us committed to precise physical symmetry are absorbed by the subtle differences in minor facet construction. They create consistent performance within our established larger proportion combinations. Having strict tolerances for all aspects of the stone, major and minor, is the way a brand acquires an identity: Brian’s ACAs have a certain visual footprint, as do Paul’s Venus by Infinity, 8* etc. Rhino has his favorite set of combinations that result in a footprint he’s studied and approved, as do R&T.

In our case, Brian’s in-depth studies drive decisions on tolerances that imbue the brand with consistent performance and the balance we desire. We have observed (as have others with reputable brands) that the performance of a true-patterned diamond with a known set of proportions is as consistent as any HCA prediction, but with an even greater level of detailed analysis. Maybe HCA2.0 will build on some of this knowledge.