Consumer advisory: GIA Cut Grade Rounding Problems

[adamasgem]

GIA, in their biweekly online newsletter "Insider" showed an openly published example of the NEW lookup tables for FacetWare, the example shown below under educational fair use

Once again, there is the typical licensing agreement you have to "agree to" to access the tables, which I haven''t done, because that would "prevent" me from reproducing in order to comment on them..

Here is the link, just in case, somehow, the complete set of tables should anonomously wind up in my email inbox..

http://www.diamondcut.gia.edu/06_estimating_a_cut_grade.html

 

[strmrdr]

http://www.diamondcut.gia.edu/pdf/6_05_RDR_pg239_243pdf.pdf

Page 4.

"Most of the observers in the GIA’s cut study found that the patterns seen in diamonds with significant painting on the crown were similar
to those seen in diamonds without painting, but some dark areas were much darker, giving an overall impression that the diamond was
not as bright. For example, the pattern radiating from the center is darker and extends further into the crown area for diamonds severely
painted on the crown (figure 8a) than for those diamonds with the same proportions that are not painted. This makes the fire (which
does not change significantly) stand out more strongly against the dark background, while it diminishes the brightness of the diamond."

Quoted for educational use.

From looking at 8* id have to agree with that.
In some light conditions the diamond itself does look darker.
Its one of the reasons I dont care for them.

 

[strmrdr]

same source this time digging:
"Severe digging out can lead to a darkening of the upper-half facets of a diamond, as the junctions between the dug-out facets become
less discernible; the result is that adjacent facets (the two upper halves) begin to look like a single large facet. This can alter scintillation or
contrast patterns (the patterns of flashing light and dark areas seen when the diamond is rocked, tilted or rotated) by causing larger
regions of the diamond to flash at the same time, thereby changing the balance of “sparkliness” and altering the pattern."

Quoted for study.

 

[strmrdr]

conclusion:
"For typical
proportion combinations, in all
cases of painting and digging out beyond a certain degree,
the observation testing (including trade observations) that
the GIA conducted as part of the development of the
upcoming GIA cut grading system confirmed that the
appearance of the diamond was less preferred than a diamond
of similar proportions with standard brillianteering."

same source, quoted for study.

 

[adamasgem]

Date: 2/14/2006 1:26:32 PM
Author: strmrdr
http://www.diamondcut.gia.edu/pdf/6_05_RDR_pg239_243pdf.pdf


Quoted for educational use.

From looking at 8* id have to agree with that. How many 8* have you looked at ???
In some light conditions the diamond itself does look darker. Would you mind defining the lighting conditions?
Its one of the reasons I dont care for them. You are entitled to your opinion, and everyone has one

Storm..
1) High optical symmetry gives improved contrast, what you might term a slightly "darker" center
2) "painting" improves edge to edge brilliance, so that the stone visually appears larger
3) High optical symmetry improves fire, and also makes the fire more discernable from greater distance
4) I believe that high optical symmetry reduces internal pathlengths such that a lower color diamond faces up a better color than would be expected..
5) High optical symmetry reduces the small breakup of patterns, which some term scintilation, HOWEVER, scintillation is lost as one moves farther away from the stone, as the human eye can''t resolve it

 

[JohnQuixote]

I have been avoiding a rush to judgment but will make a few comments here, as I see both painted and traditionally brillianteered diamonds in large numbers. Some of this will be redundant, as Marty has made similar comments.

I see clients view these types of goods side by side and hear reports from analysts and appraisers. The alleged perception of darkness does not occur in painted diamonds when good optical symmetry is present.

Optical symmetry produces less internal absorption and increased contrast even in painted diamonds. Spectral colors also become more pure with optical symmetry. Therefore you recognize fire farther away from the stone. In painted diamonds with OS you don’t get such a rapid fire scintillation (such in those with greater angular variance between crown facets), but you get larger, broadflash scintillation that's visible at a greater distance. The advantage is that you continue to see those flashes at a greater distance than with non-painted diamonds. With painting and OS the diamond also looks larger.

At some level this may be an issue where benefits of optical symmetry are not being rewarded by the lab. GIA including glare is also a can of worms and does not help this situation at all. It masks everything.

 

[strmrdr]

Date: 2/14/2006 2:29:26 PM
Author: adamasgem

Date: 2/14/2006 1:26:32 PM

Author: strmrdr

http://www.diamondcut.gia.edu/pdf/6_05_RDR_pg239_243pdf.pdf



Quoted for educational use.


From looking at 8* id have to agree with that. How many 8* have you looked at ???

In some light conditions the diamond itself does look darker. Would you mind defining the lighting conditions?

Its one of the reasons I dont care for them. You are entitled to your opinion, and everyone has one

Storm..

1) High optical symmetry gives improved contrast, what you might term a slightly ''darker'' center

2) ''painting'' improves edge to edge brilliance, so that the stone visually appears larger

3) High optical symmetry improves fire, and also makes the fire more discernable from greater distance

4) I believe that high optical symmetry reduces internal pathlengths such that a lower color diamond faces up a better color than would be expected..

5) High optical symmetry reduces the small breakup of patterns, which some term scintilation, HOWEVER, scintillation is lost as one moves farther away from the stone, as the human eye can''t resolve it

lol Marty well atleast ya didnt yell at me this time
1> exackly - they put on a real nice light show in other lighting but look dark in others to me. My preference is brighter diamonds with smaller flashes.

2> i like the girdle contrast appearance better, to me it looks more interesting.

3> large fire visible further that small sure, a wide cone of bright white light travels further yet.

4> agree there but the same affect occurs with longer lgf and classic style girdles.

5> not sure I agree with the distance thing on their hand. for someone across the room then yea.

How many have I seen:
1 for a day and a few more for a few minutes.
Seen one have seen them all right? cuz they are all the same under the firescope :}

Lighting:
lighting where the fire doesn''t come into play.
diffused fluorescent lighting,
weak lighting in my apartment. 20W compact fluorescent bulb for a 10x20 room,15w same for a 10x15 room, they all look so-so there.

Id rather talk bout what GIA said or your going to start yelling again :}

 

[adamasgem]

Date: 2/14/2006 2:57:11 PM
Author: strmrdr



lol Marty well atleast ya didnt yell at me this time
1> exackly - they put on a real nice light show in other lighting but look dark in others to me. My preference is brighter diamonds with smaller flashes. Step back a little an see when you still see the smaller flashes

2> i like the girdle contrast appearance better, to me it looks more interesting. I think you are in the minority prefering a smaller looking diamond

3> large fire visible further that small sure, a wide cone of bright white light travels further yet. I think you had better rethink your statement

4> agree there but the same affect occurs with longer lgf and classic style girdles.

5> not sure I agree with the distance thing on their hand. for someone across the room then yea. OK

How many have I seen:
1 for a day and a few more for a few minutes. I''m not sure that really qualifies you
Seen one have seen them all right? cuz they are all the same under the firescope :} EVERY diamond, I don''t care who cuts it, has its own individual character

Lighting:
lighting where the fire doesn''t come into play. Sounds like you are emulating GIA
diffused fluorescent lighting,
weak lighting in my apartment. 20W compact fluorescent bulb for a 10x20 room,15w same for a 10x15 room, they all look so-so there. What do you mean by "they", have you compared side by side under the same conditions at the same time.. probably not

Id rather talk bout what GIA said or your going to start yelling again :} I don''t yell, I just spank, and sometimes wonder where you are getting your talking points from.

 

[oldminer]

"I see clients view these types of goods side by side and hear reports from analysts and appraisers. The alleged perception of darkness does not occur in painted diamonds when good optical symmetry is present.

Optical symmetry produces less internal absorption and increased contrast even in painted diamonds. Spectral colors also become more pure with optical symmetry. Therefore you recognize fire farther away from the stone. In painted diamonds with OS you don’t get such a rapid fire scintillation (such in those with greater angular variance between crown facets), but you get larger, broadflash scintillation that''s visible at a greater distance. The advantage is that you continue to see those flashes at a greater distance than with non-painted diamonds. With painting and OS the diamond also looks larger.

At some level this may be an issue where benefits of optical symmetry are not being rewarded by the lab. GIA including glare is also a can of worms and does not help this situation at all. It masks everything."


Of all the postings on this very long and well read thread, this one stands out as useful and reasonable. I don''t see GIA being in a postiion to back out of their new grading approach, right, wrong or poorly done. No doubt, there will be many who utilize the GIA approach and we must learn how to deal with it. It sounds as if the AGS lab has done a better job and we will see how the market accepts their system, too.

My own approach will be to continue to measure diamonds for light performance and to mine the data on how they were actually cut in order to sell services to sight-holders on how best performing diamonds are cut....symmetric, dugout, pasted, whatever..... There are many variations of cutting that produce very beautiful diamonds. Without prejudice, one can take data from those that produce excellent results, regardless of cut, and learn from each diamond. I feel sure we will find literally hundreds of differing models which look superb, and meet the highest standards of durability, finish and spread ratio. The eventual intention is to offer cut consulting services based on best performance AND weight retention for rough diamonds. Right now, rough mapping and planning is done primarily on a best weight retention basis. Once a cutter can plan a high performance diamond that may bring a premium price, the game will forever be altered. It will be an entertaining journey.

 

[adamasgem]

Date: 2/14/2006 5:46:40 PM
Author: oldminer

At some level this may be an issue where benefits of optical symmetry are not being rewarded by the lab. GIA including glare is also a can of worms and does not help this situation at all. It masks everything.''

It is worse than just including the glare component. The Balck hole at the girdle plane results in an angualr input distribution that is different for each facet class., I''m talking about limiting the angle of incidence and also the instensity, non of which are real world conditions.

 

[Garry H (Cut Nut)]

Date: 2/15/2006 2:42:28 AM
Author: adamasgem

Date: 2/14/2006 5:46:40 PM
Author: oldminer


At some level this may be an issue where benefits of optical symmetry are not being rewarded by the lab. GIA including glare is also a can of worms and does not help this situation at all. It masks everything.''

It is worse than just including the glare component. The Balck hole at the girdle plane results in an angualr input distribution that is different for each facet class., I''m talking about limiting the angle of incidence and also the instensity, non of which are real world conditions.

Marty I thought I had made it very clear (with evidence from the Foundation article) to you that GIA does not use any of its original computer modeling fiasco

 

[strmrdr]

Date: 2/15/2006 4:43:18 AM
Author: Garry H (Cut Nut)

Date: 2/15/2006 2:42:28 AM

Author: adamasgem

Date: 2/14/2006 5:46:40 PM

Author: oldminer



At some level this may be an issue where benefits of optical symmetry are not being rewarded by the lab. GIA including glare is also a can of worms and does not help this situation at all. It masks everything.'

It is worse than just including the glare component. The Balck hole at the girdle plane results in an angualr input distribution that is different for each facet class., I'm talking about limiting the angle of incidence and also the instensity, non of which are real world conditions.

Marty I thought I had made it very clear (with evidence from the Foundation article) to you that GIA does not use any of its original computer modeling fiasco

That is part of the problem.
Computer modeling was a mess so they went too far the other way.
Its becoming clear to me anyway that the grading scale represents the prejudices of the trade they used for the viewing comparisons.

The biggest problem is that trade members are going to rank high what they most deal with: badly cut diamonds.
Careful reading brings up several points:

from Above: trade viewers didn't like painted/dug facets. was the problem limited data-set? Where all the painted diamonds bad ones? they just didnt like em?

steep/deep: some of the viewers rated them high so they get the EX grade.

h&a: those that looked for it rated them higher than other diamonds.

limited lighting conditions: just like no machine can grade diamond performance in one lighting condition neither can humans.
Change the lighting conditions and the ranking can and will swing a lot.

 

[adamasgem]

Date: 2/15/2006 4:43:18 AM
Author: Garry H (Cut Nut)

Date: 2/15/2006 2:42:28 AM
Author: adamasgem

Date: 2/14/2006 5:46:40 PM
Author: oldminer



At some level this may be an issue where benefits of optical symmetry are not being rewarded by the lab. GIA including glare is also a can of worms and does not help this situation at all. It masks everything.''

It is worse than just including the glare component. The Balck hole at the girdle plane results in an angualr input distribution that is different for each facet class., I''m talking about limiting the angle of incidence and also the instensity, non of which are real world conditions.

Marty I thought I had made it very clear (with evidence from the Foundation article) to you that GIA does not use any of its original computer modeling fiasco

Garry, my friend.. Their modified hemisphere with 23 degree obscuration, STILL HAS A BLACK HOLE AT THE GIRDLE PLANE, and now the angular distributional statistics are even worse. HOW CAN I MAKE MY STATEMENT CLEAR for you..

When I get a chance I''ll regenerate and post both input angular distributional models versus facet class, something you do not have the computer capability of doing... You might reread the first and last GIA article and take pencil and paper to see what I mean.. It is not a difficult proof. Read the G&G issue after the first GIA article for my letter to the editor and their mealy mouth response.

 

[JohnQuixote]

Date: 2/14/2006 5:46:40 PM
Author: oldminer

''I see clients view these types of goods side by side and hear reports from analysts and appraisers. The alleged perception of darkness does not occur in painted diamonds when good optical symmetry is present.

Optical symmetry produces less internal absorption and increased contrast even in painted diamonds. Spectral colors also become more pure with optical symmetry. Therefore you recognize fire farther away from the stone. In painted diamonds with OS you don’t get such a rapid fire scintillation (such in those with greater angular variance between crown facets), but you get larger, broadflash scintillation that''s visible at a greater distance. The advantage is that you continue to see those flashes at a greater distance than with non-painted diamonds. With painting and OS the diamond also looks larger.

At some level this may be an issue where benefits of optical symmetry are not being rewarded by the lab. GIA including glare is also a can of worms and does not help this situation at all. It masks everything.''


Of all the postings on this very long and well read thread, this one stands out as useful and reasonable. I don''t see GIA being in a postiion to back out of their new grading approach, right, wrong or poorly done. No doubt, there will be many who utilize the GIA approach and we must learn how to deal with it. It sounds as if the AGS lab has done a better job and we will see how the market accepts their system, too.

My own approach will be to continue to measure diamonds for light performance and to mine the data on how they were actually cut in order to sell services to sight-holders on how best performing diamonds are cut....symmetric, dugout, pasted, whatever..... There are many variations of cutting that produce very beautiful diamonds. Without prejudice, one can take data from those that produce excellent results, regardless of cut, and learn from each diamond. I feel sure we will find literally hundreds of differing models which look superb, and meet the highest standards of durability, finish and spread ratio. The eventual intention is to offer cut consulting services based on best performance AND weight retention for rough diamonds. Right now, rough mapping and planning is done primarily on a best weight retention basis. Once a cutter can plan a high performance diamond that may bring a premium price, the game will forever be altered. It will be an entertaining journey.

Thanks for the comment, Dave. Your sentence that I''ve highlighted is the macro of what I was trying to offer.

In this circumstance (painting), optical symmetry and specific configurations change the playing field. Stereotyping all diamonds produced using this technique is wrong because those with premium OS behave differently. It''s a symptom of the same disease where diamonds with 34.8, 34.9 and 35.0 CA are all stereotyped as 35s, even though they do not behave as 35s.

 

[WinkHPD]

Date: 2/15/2006 12:55:07 PM
Author: JohnQuixote

In this circumstance (painting), optical symmetry and specific configurations change the playing field. Stereotyping all diamonds produced using this technique is wrong because those with premium OS behave differently. It''s a symptom of the same disease where diamonds with 34.8, 34.9 and 35.0 CA are all stereotyped as 35s, even though they do not behave as 35s.

In my opinion this is a very real reason that the transparent peer review done by AGS is so superior to what GIA is doing recently. Peer review and analysis would have avoided much of the problem that GIA is currently experiencing.

Painting for example. Some painting is just plain bad. Some is quite beneficial. The link that Valeria provided us to Pete Yantzer''s explaination of painting was wonderful as it allowed us to see a short and concise explaination of a very complex issue. When presented with this complex issue, AGS took the time to figure it out, while it is seemingly apparent that GIA either did not want to do the work, or did not bother to do the work prior to declaring painting a bad thing.

To be fair, it is possible that they did do the work and still chose to declare it bad rather than having to worry about the complexities of doing it one way for one stone and downgrading another for using the "bad" painting, but since they do not share their research with the world for peer review it is impossible to know. Since I have great admiration for what GIA has done in the past and since I truly desire to start admiring their new work it hurts my heart to see them stub their toes so badly with this new project.

Now, much like the VHS and what ever the name of that other format was, it is not always the best format that the market accepts. GIA has such name recognition that it may well never matter to the masses that they have royally messed up with this, it will be GIA who is assumed to be right, even if they can be proved to be wrong. So, ???.

Time will tell.

Wink

 

[oldminer]

John:

Ultimately, I believe using predictive methods will infer that actual performance of highly similar diamonds will be nearly identical, when the fact is that they may well be quite differernt from one another.

Measuring ALL the parametric variables is a rather worthless pursuit when it comes to "HOW DOES THIS SINGLE DIAMOND PERFORM?" We don''t, won''t or can''t really measure ALL the variables and then not with distinct accuracy anyway.

The arguments over slight angles, rounding, and opinion built into software all go in a large, maddening circle. You know where I have staked out my position as do the rest of the gang here. Anyone who is not offensive, wishing to take a closer look will always be welcomed. As my cycle mechanic says, "no bozos"..........

 

[adamasgem]

Here is an example of Input Angle (angle of incidence) cummulative distribution functions for two different cuts, using the GIA 23 degree occluded hemishpere. The percentage of rays were proportional to the total area of the hemisphere generating the incident ray.

These data did not separate the input rays by whether or not the reflected ray (glare) would reflect back toward the top of the hemisphere, toward the viewer''s position, which is another problem.

One immediately notices that the INPUT distribution functions are not uniform (the straight line lower left to upper right), and do not include the intensity effect as they were done with the uniform intensity that GIA uses.

Note that while the table cannot receive low angle of incidence rays (straight in rays which reflect 17%) the other facet classes can.

All of this is not only applicable to "real world" situations, but also to machine generated lighting.

It is a complex issue... Do you look at the light return from the percentage of light intensity that actually ENTERS the diamond, which is environmentaly dependent, to assess the cutting efficiency, or do you look at composite total light return, with glare, in an artificial environment, which may or may not reflect ANY reality. You get two different answers.

 

[adamasgem]

The reflectivity from the surface of the diamond depends on the polarization of the input ray relative to the plane of incidence and the angle of incidence, as well as the index of refraction of the diamond at the wavelength sought. In theis example the middle curve represents the average (random polarization, integrating sphere model) versus that from rays polarized in the plane of incidence and perpendicular to the plane of incidence (top and bottom curves)

The amount of energy entering the diamond is 1.0 minus the reflectivity(glare).

The total energy entering the diamond is a function of the angle of incidence and the relative intensity of the light source versus wavelength.

 

[JohnQuixote]

Marty, I thought you'd switched main angle figures on the Stoephasius model until I looked it up. The calculated WLR of 0.248 in the 1998 G&G was among the lowest included. Is that why you posted that one? [ for the record here, the other cut was reported as .281 - and, GIA's calculated WLR: High (bright) > 0.285, Mod high = 0.280 to 0.285, Typical = 0.270 to 0.280, Mod low = 0.265 to 0.270 and Low (dark) < 0.265. ]

Date: 2/15/2006 2:02:55 PM
Author: adamasgem

It is a complex issue... Do you look at the light return from the percentage of light intensity that actually ENTERS the diamond, which is environmentaly dependent, to assess the cutting efficiency, or do you look at composite total light return, with glare, in an artificial environment, which may or may not reflect ANY reality. You get two different answers.

Interesting that this from the same report:

"Note that we excluded glare—that is, any light directly reflected from the top surface—from the WLR value (a difference from the GIA Diamond Dictionary definition of brilliance). We made this simple change in our computer program to guarantee that any trends in the WLR data were not simply due to an increased area of the crown acting like a front-surface reflector. However, this is also a reasonable change to the metric, since when experienced observers “rock” a diamond, they mentally correct for the effects of glare. (We also checked our results with glare included and found that although the WLR values increased across the whole range of proportions, the relative variation was essentially unchanged.)"

But now it's in. Curious.

 

[JohnQuixote]

Date: 2/14/2006 2:46:55 PM
Author: JohnQuixote


I have been avoiding a rush to judgment but will make a few comments here, as I see both painted and traditionally brillianteered diamonds in large numbers. Some of this will be redundant, as Marty has made similar comments.

I see clients view these types of goods side by side and hear reports from analysts and appraisers. The alleged perception of darkness does not occur in painted diamonds when good optical symmetry is present.

Optical symmetry produces less internal absorption and increased contrast even in painted diamonds. Spectral colors also become more pure with optical symmetry. Therefore you recognize fire farther away from the stone. In painted diamonds with OS you don’t get such a rapid fire scintillation (such in those with greater angular variance between crown facets), but you get larger, broadflash scintillation that's visible at a greater distance. The advantage is that you continue to see those flashes at a greater distance than with non-painted diamonds. With painting and OS the diamond also looks larger.

At some level this may be an issue where benefits of optical symmetry are not being rewarded by the lab. GIA including glare is also a can of worms and does not help this situation at all. It masks everything.

Pursuant to this, I found a quote I had been searching for right there in that Fall 1998 G&G Hemphill/Reinitz article:

"In addition, we plan to explore two important considerations that have been neglected thus far: symmetry and color. From our efforts and observations of actual diamonds for this study, we suspect that symmetry deviations may produce significant variation in brilliance (this was also suggested by A. Gilbertson, pers. comm., 199. Incorporation of symmetry deviations requires adding more parameters to describe the shape of the round brilliant, and devising a method of tracking multiple symmetry faults. Once this is done, the model can be used to calculate both images and metric values that show how symmetry deviations, both singly and in combination, change diamond appearance."

I wish they had been able to explore those considerations further.

This explains why Marty is hopping mad. Two of his black belts are in color and symmetry.

 

[adamasgem]

Date: 2/15/2006 6:14:14 PM
Author: JohnQuixote
Marty, I thought you''d switched main angle figures on the Stoephasius model until I looked it up. The calculated WLR of 0.248 in the 1998 G&G was among the lowest included. Is that why you posted that one? [ for the record here, the other cut was reported as .281 - and, GIA''s calculated WLR: High (bright) > 0.285, Mod high = 0.280 to 0.285, Typical = 0.270 to 0.280, Mod low = 0.265 to 0.270 and Low (dark) < 0.265. ]

Date: 2/15/2006 2:02:55 PM
Author: adamasgem

It is a complex issue... Do you look at the light return from the percentage of light intensity that actually ENTERS the diamond, which is environmentaly dependent, to assess the cutting efficiency, or do you look at composite total light return, with glare, in an artificial environment, which may or may not reflect ANY reality. You get two different answers.

Interesting that this from the same report:

''Note that we excluded glare—that is, any light directly reflected from the top surface—from the WLR value (a difference from the GIA Diamond Dictionary definition of brilliance). We made this simple change in our computer program to guarantee that any trends in the WLR data were not simply due to an increased area of the crown acting like a front-surface reflector. However, this is also a reasonable change to the metric, since when experienced observers “rock” a diamond, they mentally correct for the effects of glare. (We also checked our results with glare included and found that although the WLR values increased across the whole range of proportions, the relative variation was essentially unchanged.)''

But now it''s in. Curious.

Actually, I just scrolled down until I found a somewhat different cut than the Tolkowsky model and ran the 100000 ray raytrace analysis to generate the plot..

Interesting quote from GIA on the glare issue, an about face in thinking???
It must have made their data ranges for EX wider

 

[JohnQuixote]

Date: 2/15/2006 1:35:20 PM
Author: Wink

In my opinion this is a very real reason that the transparent peer review done by AGS is so superior to what GIA is doing recently. Peer review and analysis would have avoided much of the problem that GIA is currently experiencing.

Painting for example. Some painting is just plain bad. Some is quite beneficial. The link that Valeria provided us to Pete Yantzer's explaination of painting was wonderful as it allowed us to see a short and concise explaination of a very complex issue. When presented with this complex issue, AGS took the time to figure it out, while it is seemingly apparent that GIA either did not want to do the work, or did not bother to do the work prior to declaring painting a bad thing.

Wink, did you see the quote above from the Fall 1998 G&G on symmetry and color? GIA did have plans to devise a method of tracking symmetry faults, the converse results of which would have illuminated the beneficial aspects of symmetry (painted or otherwise) for them I'd think - if they had followed up.

From conversations with Peter I think AGS did take time to understand the potential for both good and bad in brillianteering, and in the AGS metric those benefits are accounted for elegantly via light performance measure - as is symmetry to a degree...I wonder who will be the first major lab to step up and make comment about optical symmetry on a report, even if it's not 'graded.'

 

[RockDoc]

RE: Optical Symmetry.....


John, I think at the conclave in April, AGS may have their software ready that SHOULD take the ASET images into consideration.

I would assume that this is a part of the light performance analysis, on the AGS grading reports where a light performance rating is provided. So far on those reports, I''ve only seen Light Performace graded as a 0. It will be interesting to see some reports that maybe grade light performance differently ( 1,2, 3 etc) as well as the ASET image being incorporated into the report, and see what the differences are.

I would also like to see their reports amended to show the LGF measurements too, as well as a few other things.

Since concalve is the end of April, we probably won''t have to wait very long.

It would even be more interesting, to see a grading conclusion for painting, so that the average consumer can more readilly understand good and bad painting techniques in the report.

Rockdoc

 

[adamasgem]

Date: 2/16/2006 1:14:12 PM
Author: JohnQuixote

Wink, did you see the quote above from the Fall 1998 G&G on symmetry and color? GIA did have plans to devise a method of tracking symmetry faults, the converse results of which would have illuminated the beneficial aspects of symmetry (painted or otherwise) for them I''d think - if they had followed up.

From conversations with Peter I think AGS did take time to understand the potential for both good and bad in brillianteering, and in the AGS metric those benefits are accounted for elegantly via light performance measure - as is symmetry to a degree...I wonder who will be the first major lab to step up and make comment about optical symmetry on a report, even if it''s not ''graded.''

John..

It appears that other than the "qualitative" assessment of symmetry, GIA has completely ignored the primary aspects of symmetry in their cut grade.

It appears that AGS ray traces each and every stone based on its individual scan, while it also appears that GIA takes a scan, averages, rounds hapazardly, redefines meanings of "subjective" words like "medium girdle, and then uses a lookup table. And GIA did all that after spending how many milliions of industry dollars.

 

[WinkHPD]

Date: 2/16/2006 1:28:46 PM
Author: RockDoc
RE: Optical Symmetry.....


John, I think at the conclave in April, AGS may have their software ready that SHOULD take the ASET images into consideration.

I would assume that this is a part of the light performance analysis, on the AGS grading reports where a light performance rating is provided. So far on those reports, I''ve only seen Light Performace graded as a 0. It will be interesting to see some reports that maybe grade light performance differently ( 1,2, 3 etc) as well as the ASET image being incorporated into the report, and see what the differences are.

I would also like to see their reports amended to show the LGF measurements too, as well as a few other things.

Since concalve is the end of April, we probably won''t have to wait very long.

It would even be more interesting, to see a grading conclusion for painting, so that the average consumer can more readilly understand good and bad painting techniques in the report.

Rockdoc

I will be attending a class at AGS next week along with 30 or so other excited students of their new cutting system. I am hoping that we will get a preview of not only the software but the new parameters for the AGS ideal emerald cut. These are EXCITING times! Both Pete Yantzer and Jim Caudill will be there as instructors for this two day class so we will have some "pick your brain" time with two of the best.

I know that Pete has been following this conversation, at least earlier on, I will ask him if he got a chance to come see some of the recent posts and what he may or may not have to say about them at this time...

Wink

 

[Garry H (Cut Nut)]

Wink I hope you can get a good handle on the AGS Fire method ( I posted one of their Fire charts here https://www.pricescope.com/community/threads/cut-geeks-only-hca-approved-gia-excellents.40342/ ).

It will also be good to know what range and weighting Peter''s team have finally settled on for ASET images. I think about 45 degrees each side (90 in total) with a harsh COS taking the results to zero at 45 tilt would do the job nicely. But Fire is still interesting at any amount of tilt.

It is an intriguing idea - but I am not completely convinced - although that chart does show some comon sense making patterns (I like common sense - pity it is so uncommon

)

Marty they did lots of looking in domes that may have been somewhat related to computer models - but they did say that only 58%? of human observers in the light box matched those computer predictions.

Computers shomoters seems to be applicable.

The simpler fact remains - a 46 degree obstruction zone matched their lighting environment human observer results (please - why keep referring to GIA''s 23 degrees - AGS used 30 degrees and 40 degrees ASET blue to represent obstruction, I use 25 degree for ideal-scope. If you use 23 degree, then we all have to change to 15 and 20 and 12.5).

46 degrees makes Tolkowsky llook bad. AGS showed that - that is why they stopped at 40 degrees. The GIA research team should have realized they were making bo-bo''s when they got a 46 degree obstruction model!!!!!!

 

[strmrdr]

Wink,
Few questions for AGS if you would :}

Ask if helium scans will be used for EC''s given the problems with the current sarin machines in tracking facets on them.
Have they been working with sarin to fix the problem if not?

photo capable aset?? is one planned

Have they considered a cert lookup website that displays the ASET images that went into the cut grade when you input the cert #?

Aset images printed on the cert would be nice. :}

snag me a copy of the S.E. chart! :}

I may come up with more when im awake.

 

[adamasgem]

Date: 2/17/2006 1:57:58 AM
Author: Garry H (Cut Nut)
Wink I hope you can get a good handle on the AGS Fire method ( I posted one of their Fire charts here https://www.pricescope.com/community/threads/cut-geeks-only-hca-approved-gia-excellents.40342/ ).

It will also be good to know what range and weighting Peter''s team have finally settled on for ASET images. I think about 45 degrees each side (90 in total) with a harsh COS taking the results to zero at 45 tilt would do the job nicely. But Fire is still interesting at any amount of tilt.

Unfortumately the png files showing the tilt effects are too large to post here on pricescope. I put one composite show 30 deg bluw/40 deg blue an file versus 1 degree tilt increlents for the tolkowsky cut on my web site..

http://www.adamasgem.org/pngs/tolk.png

And these have been done for all the oublished GIA cuts..aand I assure you that AGS have been seriously looking at the tilt aspect, but it is computor intensive process. I thank Pete Yantzer for this data and take some credit for pushing their research. AGS, unlike GIA is very receptive to ideas, and tackle them subject to their limited resources and priorities. Oh what they could do with the monies GIA squandered,

 

[adamasgem]

Date: 2/17/2006 1:57:58 AM
Author: Garry H (Cut Nut)

Marty they did lots of looking in domes that may have been somewhat related to computer models - but they did say that only 58%? of human observers in the light box matched those computer predictions.

I going to buy some 4 inch white acrylic domes, and then model what is really happening in their observational testing.

Al Gilbertonson had the right conceptual idea when he did the testing with the variable domes, HOWEVER the "technical" types which came up with the theoretical models for the domes Al used, seemingly had there heads up their backsides, if their final uniiform uniform (46/23) intensity dome is any examole, as I strongly believe the model they came up with does not accurately reflect the physical envirornment they tried to simulate and correlate with "observations".

Back ot the envelope seemingly calcs show this out, and I''ll be talking with Seregy about it.

This is going to be peer review with a cattle prod

 

[Garry H (Cut Nut)]

Date: 2/17/2006 5:11:47 AM
Author: adamasgem

Date: 2/17/2006 1:57:58 AM
Author: Garry H (Cut Nut)

Marty they did lots of looking in domes that may have been somewhat related to computer models - but they did say that only 58%? of human observers in the light box matched those computer predictions.

if their final uniiform uniform (46/23) intensity dome is any examole, as I strongly believe the model they came up with does not accurately reflect the physical envirornment they tried to simulate and correlate with ''observations''.

That is the point Marty - the whole point and nothing but the point.

They made a model because of their computer study to try to legitimize the money and decade they had wasted.
They made a model that matched their lighting box DiamondDock CVE results, which had too much concentrated light coming from a narrow direction. The plastic salad bowl dome that matched this had a huge amount of obstruction darkness around the observer because in many rooms these 2 strong fluoro tubes and 12 LED intense spots (relative to often dull room lighting) made anything but steep deep proportioned stones look dead.

They then took that model and showed that they could indeed make a computer model that had a 58% level of accuracy. Hello?

They messed up in the human observer section.
But it will be good for business. But what if the world wakes up and realises that the worlds formeost authority either made a mistake or made a commercial decison?