GIA Diamond Dock. - simple summary

[Garry H (Cut Nut)]

In reference to my Journal Article GIA Excellent Cut grades: A case study there have been a number of related threads that seem to have gotten a bit confusing.

These are those threads:
GIA Diamond Cut Grading: Problems with Diamond Dock (Leonid and Sergey) This thread is about the same topic as the Journal Article - the development of GIA's. Why do some diamonds look good and some look bad in GIA's Diamond Dock(r). We discuss a Shallow GIA Very good, and 2 GIA Excellent Cut stones: A nice normal Tolkowsky stone and a stone that is Steep Deep (near the GIA boundary.

GIA EX: Let the buyer beware... (John Quiote) John and Brian the Cutter are concerned about GIA's grading results.

GIA Ex: The Consumers Perspective and the Technologies (Rhino) did a small survey with painted and non painted stones in his store using Diamond Dock. He likes it, but unfortunately he has still not read my article.

Peter Yantzer - the Director of AGS Laboratories has kindly run the 3D scans for all the diamonds in all these discussions.

THe results of his scans have been presented in a novel way - the light return from as a % broken down into angular directions. 0 degrees would be light from the horizon - and 90 degrees is from directly overhead.

From the bar chart we can see the deeper stone (one first posted by Rhino and not the one in my study) has very good light return in the shallower angles - a whole 1/4 of its brightness and sparkle comes from lights in that area (from high windows for example, when the viewer is looking downwards to the diamond.) but the shallow stone gathers only 2.5% (1/10th as much) from that direction.

55% of the shallow stones light comes from the premium area where the most lighting is in the most common environments - the ceiling.

So when you examine a shallow diamond in Diamond Dock - it does not have as much bright sparkle as a deeper diamond.

a Tolkowsky 'Ideal' does very well across a broad range.

I hope you find this is interesting and comprehensable.

(BTW the other threads have desolved into more 8* and New Line wars discussing painted and branded diamonds and how they will be graded by GIA / AGS etc. The evidence suggests that this is a swings and roundabouts debate and personal preference plays a big role. I do not believe the soulution to this debate is simple - it invloves very complex studies - and does not affect the main stream market - that is why i started a new thread. I would prefer any debate about painting stayed on those other threads.)

 

[strmrdr]

interesting...
The chart indicates to me that shallow and slightly deep dimonds would be better suited for pendants and earrings and ideal cuts for rings.
Which is supported by some of my other studies.

 

[JohnQuixote]

Thanks for separating a simple summary Garry.

In the spirit of supporting such summary, here are GIA and AGS cut comparison charts - for those interested in proportions combinations.

 

[Garry H (Cut Nut)]

Thanks for adding the charts Sir john QuickOates

(private joke)

I played with DiamCalc and made a new ASET.

This shows just how arbitrary an grading system can be - who is to say where the light should come from that defines a good diamond?

But this certainly shows where the light comes from in a steep deep diamond - and as we can see - the most obvious thing is that not much comes from above the diamond. GIA has a cut grading system for people who live in rooms full of windows. I guess they should not throw stones

If it is not clear please ask for more info

 

[Serg]

re: Garry picture DD GIA with angles.

In other words : In vertical plane GIA use +30 degree head obscuration for upper head part ( in two times more at least than real head obscuration from upper head part)

It is reason why shallow diamonds looks worse in DD GIA.

 

[Garry H (Cut Nut)]

Date: 3/26/2006 1:05:27 AM
Author: Serg
re: Garry picture DD GIA with angles.

In other words : In vertical plane GIA use +30 degree head obscuration for upper head part ( in two times more at least than real head obscuration from upper head part)

It is reason why shallow diamonds looks worse in DD GIA.

Actually Sergey they explain in the Foundation article that they use 23 degrees each side (46 degrees in total) obscured by dak area in a white dome.

This is the same as 90-23= 67 for AGs charts above

 

[Rhino]

Sorry for not being able to respond earlier guys. No disrespect mate but I am finding the exact opposite of what you're claiming. When I find some time to break away I'll expound with some photography to demonstrate what our eyes are seeing.

Peace,

 

[Garry H (Cut Nut)]

Date: 3/26/2006 7:12:12 PM
Author: Rhino
Sorry for not being able to respond earlier guys. No disrespect mate but I am finding the exact opposite of what you''re claiming. When I find some time to break away I''ll expound with some photography to demonstrate what our eyes are seeing.

Peace,

It is unlikely that you could see different results in the case of these stones Rhino. And the reasons why they behave as they do is apparent from Peter''s AGS ASSET info.

Rhino if you do do any work - please give examples that are relevant to the types of stones I am discussing.

And please feel free to criticise all or any of my proceedures.

It is worth stressing that GIA experimented with white domes with peep holes and 46 degrees of darkness at the top of the domes.
These three Diamcalc photo''s show what my shallow, ideal and deep stones would look like through a red reflector / ideal-scope with 46 degree obstruction.

I am sure you can agree that the steep deep stone is returning just as much red as the ideal - and the shallow stone appears much to dark in this type of red reflector.

GIA essentially used this type of device - except the red was white.
and they describe how this device worked with their observation testing.

So Rhiino - please challenge me - but please do not waste time taking loads of photo''s that do not prove anything - and please try looking at diamonds further away from light sources.

 

[Garry H (Cut Nut)]

Migrating a discussion from https://www.pricescope.com/community/threads/why-would-anyone-object-to-painting.45579/page-7
to this post because the discussion is off topic on the other thread.

Here are my compsarison photo''s Rhino.
Perhaps I need to bump up the over all lighting levels a bit. But it is pretty close I think.

 

[Rhino]

Hey Garry,

Thanks for the bump in the other thread. Reminded me of what I needed to post here for ya.

Ok ... regarding this discussion I''d like to address an issue in your journal article which I felt was entirely off base which was the comment you made "The lighting GIA used in the survey skewed observer preferences toward deeper smaller diameter diamonds (commercially favourable)."

When I had written my response to this (on our site) I addressed the issue comparing what you are describing above alongside a GIA Ex/AGS Ideal to demonstrate that deeper smaller diameter diamonds do not appear favorable. You had written back correcting me stating that if one were to compare shallow angled combos alongside deeper smaller diameter diamonds that that would be the case. Again, I do not agree. Case in point, the observation and photography below. The shallow stone on the left has an average 39.4 pavilion angle (crown around 38 degrees) alongside an old mine which is a steep/deep. The difference in brightness is pretty obvious to me and goes entirely counter to your comment in the journal article.

 

[Rhino]

Here''s the Gem Advisor file on the shallow pavilion angled stone.

 

[Garry H (Cut Nut)]

Rhino you have a deepish stone there with that crown angle.

I am afraid I can not help you get this right.

Can I skype you from here in Rome?
Email me your phhone #

 

[Garry H (Cut Nut)]

Rhino in the thread https://www.pricescope.com/community/threads/why-would-anyone-object-to-painting.45579/page-8 I asked you to take some photo’s at the GIA’s recommended angle of 45° (which is clearly shown in the instruction manual PDF you emailed to me and copied here with one red line added) - but in fact we can see from the old cut (with unknown proportions) that it is clearly facing directly at a light – this means it is even further away from 45 degrees - an even more extreme angle than all your previous video''s and other examples. (Are you marrie to this light box?). The ''shallow stone'' (a bad example because it is a fish eye with a large table and very steep crown angle – with a lot of deep stone type leakage), but at this steep angle it does serve to demonstrate what I expected – at a steep angle – the DD would lead one to prefer shallower stones over deeper ones. So even without trying to help - it is again Game, set and match.

It is also interesting that the manual suggests you dim the room lights – I believe your positive consumer response surveys were done in your store (from higher standing at counter top viewing angles) with a lot of store lighting? I have seen a shot in your office environment which also clearly shows 2 large fluoro lights that appear to be coming from over each of the observer shoulders.

So on balance it seems that, without trying too help resolve the issues with DD, you have provided ample evidence that it is not an adequate grading environment.

If you wish to co-operate we could conduct some proper tests to enable the optimum viewing angle.

 

[adamasgem]

Date: 6/11/2006 4:25:28 AM
Author: Garry H (Cut Nut)

Rhino in the thread https://www.pricescope.com/community/threads/why-would-anyone-object-to-painting.45579/page-8 I asked you to take some photo’s at the GIA’s recommended angle of 45° (which is clearly shown in the instruction manual PDF you emailed to me and copied here with one red line added) - but in fact we can see from the old cut (with unknown proportions) that it is clearly facing directly at a light – this means it is even further away from 45 degrees - an even more extreme angle than all your previous video''s and other examples. (Are you marrie to this light box?). The ''shallow stone'' (a bad example because it is a fish eye with a large table and very steep crown angle – with a lot of deep stone type leakage), but at this steep angle it does serve to demonstrate what I expected – at a steep angle – the DD would lead one to prefer shallower stones over deeper ones. So even without trying to help - it is again Game, set and match.

It is also interesting that the manual suggests you dim the room lights – I believe your positive consumer response surveys were done in your store (from higher standing at counter top viewing angles) with a lot of store lighting? I have seen a shot in your office environment which also clearly shows 2 large fluoro lights that appear to be coming from over each of the observer shoulders.

Turn off all the lights!!!!! Maybe the KD is NOT meant to be used in a jewelry store counter envirionment.

 

[pricescope]

Insider Gemologist: How Do GIA Students Visually Estimate the Brightness of a Diamond?

...Diamond appearance is very sensitive to changes in lighting conditions, so the same diamond can look quite different when viewed under different types of lighting in different positions....

 

[Garry H (Cut Nut)]

After the close of the GIA Symposium in San Diego a group of us were able to experiment with (but not photograph in) the GIA Diamond Dock(TM) at a GIA Cut Grading course.

We noted different instructors assessed 'brightness' using differing lighting / observer angles with the light box (and other light sources, like the small fluorescent lights on microscopes) and when asked about the correct lighting / observer angle the instructors had no consistent or quantifyable recommendation. As shown above in the original Diamond Dock(R) users manual a recommendation is made that the observer views diamonds at an angle of 45° to the verticle plane, which we believe was the same angle observers used for the survey testing of 70,000+ observations that formed the basis of GIA's new Cut system.

Anecdotal information from volunteers who participated in GIA's observation testing seems to confirm that observation tests were performed in a seated position that would have subtended an angle of 40° to 45° between the stones and the center of the lights (depending on observer height).

When the incident light from the fluorescent tubes comes from this angle slightly shallower diamonds have less brightness in Diamond Dock(r) where as Tolkowsky proportioned and deeper diamonds appear brighter.

We were able to demonstrate how important this viewing position is to two GIA instructors, who by their own choice, viewed diamonds from a much higher view point than 45°; one where the incident light would have been subtending an angle of approximately 20° to 30° relative to the verticle and the light source.

We had with us two of the diamonds used in my original article - the 1.19ct with proportions very near Tolkowsky's that had been graded Excellent by GIA Gem Trade Lab, and the shallow 1.16ct stone graded Very Good (painted and a border line Good when using Facetware(TM)).

From the higher viewing angle both instructors preferred the shallow stone for brightness (and were split one each for fire using the instruments LED lighting only). This set of images below shows these two stones modelled in DiamCalc along with the steep deep diamond that I did not have with mefrom the original article; this demonstration can be used to explain why the shallower stone appears brighter when the incident light comes from a higher angle; the shallower diamond draws and returns more light from directly above, while as round diamonds get deeper they draw more light from lower angles closer to the horizon. This is a similar modelling software www.cutstudy.com/cut/english/grading1/sphere1.htm



The steeper lighting-viewing angle makes most round diamonds look brighter, which probably explains why Diamond Dock(r) users seem to naturally prefer to view diamonds from higher angles than the original designers intended. We believe GIA would have arrived at quite different Excellent proportion parameter sets had the observers in their observation tests been directed to use a higher viewing angle; however as we have shown the lighting box brightness, background and narrow source of angular size of lighting would still not be a useful cut grading technique. In particular this lighting environment would have even less validity for brightness grading of fancy shaped diamonds which tend to gather light from more the lower part of the hemisphere.

 

[Garry H (Cut Nut)]

This shows a blow up of one of the ETAS maps - the 1.29ct.
Each circle is 10 degrees further out from the zenith. Note the other stones have less flares past the 40 degree point - so this stone shows - as we expect - more green thru an ASET

 

[adamasgem]

Date: 10/25/2006 4:47:29 PM
Author: Garry H (Cut Nut)

After the close of the GIA Symposium in San Diego a group of us were able to experiment with (but not photograph in) the GIA Diamond Dock(TM) at a GIA Cut Grading course.

We noted different instructors assessed ''brightness'' using differing lighting / observer angles with the light box (and other light sources, like the small fluorescent lights on microscopes) and when asked about the correct lighting / observer angle the instructors had no consistent or quantifyable recommendation. IAs shown above in the original Diamond Dock(R) users manual a recommendation is made that the observer views diamonds at an angle of 45° to the verticle plane, which we believe was the same angle observers used for the survey testing of 70,000+ observations that formed the basis of GIA''s new Cut system.

Anecdotal information from volunteers who participated in GIA''s observation testing seems to confirm that observation tests were performed in a seated position that would have subtended an angle of 40° to 45° between the stones and the center of the lights (depending on observer height).

When the incident light from the fluorescent tubes comes from this angle slightly shallower diamonds have less brightness in Diamond Dock(r) where as Tolkowsky proportioned and deeper diamonds appear brighter.

We were able to demonstrate how important this viewing position is to two GIA instructors, who by their own choice, viewed diamonds from a much higher view point than 45°; one where the incident light would have been subtending an angle of approximately 20° to 30° relative to the verticle and the light source.

We had with us two of the diamonds used in my original article - the 1.19ct with proportions very near Tolkowsky''s that had been graded Excellent by GIA Gem Trade Lab, and the shallow 1.16ct stone graded Very Good (painted and a border line Good when using Facetware(TM)).

From the higher viewing angle both instructors preferred the shallow stone for brightness (and were split one each for fire using the instruments LED lighting only). This set of images below shows these two stones modelled in DiamCalc along with the steep deep diamond that I did not have with mefrom the original article; this demonstration can be used to explain why the shallower stone appears brighter when the incident light comes from a higher angle; the shallower diamond draws and returns more light from directly above, while as round diamonds get deeper they draw more light from lower angles closer to the horizon. This is a similar modelling software www.cutstudy.com/cut/english/grading1/sphere1.htm



The steeper lighting-viewing angle makes most round diamonds look brighter, which probably explains why Diamond Dock(r) users seem to naturally prefer to view diamonds from higher angles than the original designers intended. We believe GIA would have arrived at quite different Excellent proportion parameter sets had the observers in their observation tests been directed to use a higher viewing angle; however as we have shown the lighting box brightness, background and narrow source of angular size of lighting would still not be a useful cut grading technique. In particular this lighting environment would have even less validity for brightness grading of fancy shaped diamonds which tend to gather light from more the lower part of the hemisphere.

Garry
1) The KittyDock(TM) is an assymetric lighting envirionment

2) RBC Diamonds have their highest efficiency for light return from high angle lighting,
I''ve shown it before on some thread on PS.. when I did the study of Weighted Light Return forward ray trace, and I believe I also sent you a pdf of the studies I did to try to duplicate GIA''s original #D Ray trace results. You can look at my trials and tribulations in this effort on http://www.adamasgem.org/pdfs/ray3dv.pdf. The document is somewhat organized, and has a comaprison of a 18" overhead flourescent lighting model with a WLR cosine squared metri..

3) As you standup to view in the KittyDock, while still keeping the table perpendicular to your line of sight,you get more high angle lighting, different results

4) The KittyDock(TM) doesn''t, and can''t, give you the same relative results as the symmetric hemispherical lighting model GIA say is the basis for FarceWare(TM). The scatter in GIA''s visual studies show that clearly..Every relative measure is lighting envirionment dependent, and the KittyDock(TM) doesn''t provide a consistent visual measure for grading.

GIA never published, to my knowledge, the visual comparisons results, in hemispherical envirionments vis-a-vie the variable environment KittyDock(TM). Might be interesting, I doubt they correlate vary well..

Their "results" show how they (GIA) can waste millions of dollars supplied by the trade, to come up with "results" that say that most diamonds are EX.. (of course a lot of the trade like that) ..

I don''t see how anyone in the trade who produces well cut stones, would bother to use GIA paper which lumps what we considered off make stones into the same category as well cut stones. FarceWare(TM) is BS

AGS has done a much better theoretical work...

 

[Garry H (Cut Nut)]

Date: 10/26/2006 1:39:31 AM
Author: adamasgem

Date: 10/25/2006 4:47:29 PM
Author: Garry H (Cut Nut)


After the close of the GIA Symposium in San Diego a group of us were able to experiment with (but not photograph in) the GIA Diamond Dock(TM) at a GIA Cut Grading course.

We noted different instructors assessed ''brightness'' using differing lighting / observer angles with the light box (and other light sources, like the small fluorescent lights on microscopes) and when asked about the correct lighting / observer angle the instructors had no consistent or quantifyable recommendation. IAs shown above in the original Diamond Dock(R) users manual a recommendation is made that the observer views diamonds at an angle of 45° to the verticle plane, which we believe was the same angle observers used for the survey testing of 70,000+ observations that formed the basis of GIA''s new Cut system.

Anecdotal information from volunteers who participated in GIA''s observation testing seems to confirm that observation tests were performed in a seated position that would have subtended an angle of 40° to 45° between the stones and the center of the lights (depending on observer height).

When the incident light from the fluorescent tubes comes from this angle slightly shallower diamonds have less brightness in Diamond Dock(r) where as Tolkowsky proportioned and deeper diamonds appear brighter.

We were able to demonstrate how important this viewing position is to two GIA instructors, who by their own choice, viewed diamonds from a much higher view point than 45°; one where the incident light would have been subtending an angle of approximately 20° to 30° relative to the verticle and the light source.

We had with us two of the diamonds used in my original article - the 1.19ct with proportions very near Tolkowsky''s that had been graded Excellent by GIA Gem Trade Lab, and the shallow 1.16ct stone graded Very Good (painted and a border line Good when using Facetware(TM)).

From the higher viewing angle both instructors preferred the shallow stone for brightness (and were split one each for fire using the instruments LED lighting only). This set of images below shows these two stones modelled in DiamCalc along with the steep deep diamond that I did not have with mefrom the original article; this demonstration can be used to explain why the shallower stone appears brighter when the incident light comes from a higher angle; the shallower diamond draws and returns more light from directly above, while as round diamonds get deeper they draw more light from lower angles closer to the horizon. This is a similar modelling software www.cutstudy.com/cut/english/grading1/sphere1.htm





The steeper lighting-viewing angle makes most round diamonds look brighter, which probably explains why Diamond Dock(r) users seem to naturally prefer to view diamonds from higher angles than the original designers intended. We believe GIA would have arrived at quite different Excellent proportion parameter sets had the observers in their observation tests been directed to use a higher viewing angle; however as we have shown the lighting box brightness, background and narrow source of angular size of lighting would still not be a useful cut grading technique. In particular this lighting environment would have even less validity for brightness grading of fancy shaped diamonds which tend to gather light from more the lower part of the hemisphere.

Garry
1) The KittyDock(TM) is an assymetric lighting envirionment

2) RBC Diamonds have their highest efficiency for light return from high angle lighting,
I''ve shown it before on some thread on PS.. when I did the study of Weighted Light Return forward ray trace, and I believe I also sent you a pdf of the studies I did to try to duplicate GIA''s original #D Ray trace results. You can look at my trials and tribulations in this effort on http://www.adamasgem.org/pdfs/ray3dv.pdf. The document is somewhat organized, and has a comaprison of a 18'' overhead flourescent lighting model with a WLR cosine squared metri..

3) As you standup to view in the KittyDock, while still keeping the table perpendicular to your line of sight,you get more high angle lighting, different results

4) The KittyDock(TM) doesn''t, and can''t, give you the same relative results as the symmetric hemispherical lighting model GIA say is the basis for FarceWare(TM). The scatter in GIA''s visual studies show that clearly..Every relative measure is lighting envirionment dependent, and the KittyDock(TM) doesn''t provide a consistent visual measure for grading.

GIA never published, to my knowledge, the visual comparisons results, in hemispherical envirionments vis-a-vie the variable environment KittyDock(TM). Might be interesting, I doubt they correlate vary well..

Their ''results'' show how they (GIA) can waste millions of dollars supplied by the trade, to come up with ''results'' that say that most diamonds are EX.. (of course a lot of the trade like that) ..

I don''t see how anyone in the trade who produces well cut stones, would bother to use GIA paper which lumps what we considered off make stones into the same category as well cut stones. FarceWare(TM) is BS

AGS has done a much better theoretical work...

Your on the money Marty.

This is a slide from the Vegas presentation that says a lot.

It is a cut grade system designed by many departments each with a different set of requirements.

I think they could have argued for days as to which label went in which area.
Taste preference and Predictive should surely have been closer to Scientific?

But no - they are seperated by accessable and practical. Kind of a ''dumbed down'' admission.

 

[Serg]

Garry,
re:This is a slide from the Vegas presentation that says a lot.


Well done.
Perfect shot.