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Letter to the Editor of the Australian Gemmologist

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pricescope

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adamasgem

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Geeze.. I thought that we covered the five(GIA) versus 11 grade(AGS) math before here on Pricescope.

And clearly showed the argument doesn''t work. Let alone the loosening of other "standards" by GIA..

Don Q.. do you have the link??

I note with humor the comment regarding FarceWare(TM) sales in a downward spiral.
 

strmrdr

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interesting reading,,,
arms not up to going over whats been discussed a billion times here so not going to comment more.
Thanks Garry and PS for bringing it too us too read.
 

Garry H (Cut Nut)

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Date: 2/24/2007 7:31:36 PM
Author: strmrdr
interesting reading,,,
arms not up to going over whats been discussed a billion times here so not going to comment more.
Thanks Garry and PS for bringing it too us too read.
You have a good understanding of these issues Storm, as good as any non-trade person I know. But there are many in the industry who will probably not bother to follow these arguements in detail.

However there is now one place document / where we have listed all the short comings ogf the GIA cut grading system in detail, and made it as easy to understand as we can.

We were surprised and pleased that the GIA team came out into the open to rebut our arguements, and we feel that our answers give such a strong case that they should reconsider their system as it currently exists.

Time will tell.
 

strmrdr

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I hear ya Garry...

To be honest the more I learn about the cut grading systems the less I like them GIA more so than AGS.
Why?
For the simple reason that Iv walked into jewelery stores and have been told that GIA EX cut and AGS0 cut is the best in the world and that all of them are just the greatest/best/most awesome.
We know that isn''t true.
Are we just too picky?
At times I am but over time have tempered it with reality a little more but that is way too far a stretch for me to agree with.
But there are a lot of people that will fall for it hook line and sinker.

Is that consumer well served?
Compared to a lot of diamonds out there I''d say YES but will the diamond always live up to that billing NO.
Therefore its not a good thing.

Which brings me to the matter of fault.
Is it the Jewelers fault for believing in the labs?
The labs themselves?
The consumer for not doing more research?

interesting topic indeed.......
 

adamasgem

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Date: 2/25/2007 1:45:53 AM
Author: strmrdr
But there are a lot of people that will fall for it hook line and sinker.

Is that consumer well served? Not by the GIA FarceWare(TM) or Certifigate
Compared to a lot of diamonds out there I''d say YES but will the diamond always live up to that billing NO.
Therefore its not a good thing.

Which brings me to the matter of fault.
Is it the Jewelers fault for believing in the labs? Depends on what lab they "believe" in
The labs themselves? Surely some in the selfproclaimed "world''s Fooremost Authority" take the blame there
The consumer for not doing more research? No, they are mostly subjected to hype and misrepresentation..The internet has helped a few retailers clean up their act.

interesting topic indeed.......Couldn''t agree with you more..
 

adamasgem

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Date: 2/24/2007 11:17:30 PM
Author: Garry H (Cut Nut)

We were surprised and pleased that the GIA team came out into the open to rebut our arguements, and we feel that our answers give such a strong case that they should reconsider their system as it currently exists.
Seems to me that the GIA team may be suffering from hoof in mouth disease from their response..


 

diagem

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Date: 2/24/2007 1:04:44 PM
Author:Pricescope
The Cut Group* published a letter to the Editor of the Australian Gemmologist regarding GIA Cut Grading System (with permission of the Australian Gemmologist).


* Members of the Cut Group include:



Sergey Sivovolenko, OctoNus, Finland, Tampere
Garry Holloway, Melbourne, Australia
Yuri Shelementiev, Head of Gemological Center MSU, Moscow, Russia
Janak Mistry, Lexus, Surat, India
Very Interesting Article, thank you for sharing with us on PriceScope's open/public forum....
I want to congratulate "THE CUT GROUP" on tackling this subject in a professional debate. As I read both letters..., I can relate to both sides and in my view..., Both sides make sense in their arguments..., let see the outcome, will be INTERESTING!!!!
Like most of you know, I am not big on Ideal Diamond issues, but this is important news to our industry!!! The fact that the GIA is willing listening and enter into a debate/dialogue on (any) issues might be the start of more important issues coming-up in the Diamond-Cutting category! Especially the Fancy-Shape Category...

I would like to follow through and I hope to see how the GIA's Cut Group bring this debate to the next level!!!

I cant imagine the GIA leaving this issue unanswered..., after all there question (?) marks left open!

Thank you,
 

JohnQuixote

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Date: 2/24/2007 5:01:49 PM
Author: adamasgem
Geeze.. I thought that we covered the five(GIA) versus 11 grade(AGS) math before here on Pricescope.

And clearly showed the argument doesn't work. Let alone the loosening of other 'standards' by GIA..

Don Q.. do you have the link??

I note with humor the comment regarding FarceWare(TM) sales in a downward spiral.
Don Corleone.. here it is.


https://www.pricescope.com/community/threads/ags-and-gia-cut-comparison-charts.41793/

Re. comparisons: AGS does not publish parametric 'charts,' they provide guidelines for manufacture & results may vary depending on the particulars of all 57 facets. I gave an overview 4 posts down on this page for any interested (that conversation grew legs for a plethora of different reasons). So, the above is good for width-of-range comparisons but not border-grades.

Going further; when looking at overall cut grade AGS only considers 'Ideal' finish. GIA allows EX and VG, which is logical since there is no difference between them to normal human vision.
 

tanalasta

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Interesting article. I wonder what the ramifications would happen if the GIA did withdraw their cut-grading system immediately as the letters have proposed. The gradings have influenced tens of billions of diamond sales and the GIA, jewellers and consumers have been led to believe a GIA 'excellent' cut is well ... an 'excellent' cut. If the grading system was withdrawn, would consumers believe that that 'excellent' grading is no longer of worth and invalidated? Would they then believe their diamond may be 'inferior' and/or seek compensation because they were led to believe that it was worth paying the extra for?

Picture this scenario:
When the layman wants to buy a diamond ring, he (or she) simply glances at the carat weight, clarity, colour... then see the words 'excellent excellent excellent' on a GIA certificate ... and goes 'so that's the best that I can buy?'. They don't necessarily understand proportion sets, scintillation, brilliance and the studies used to measure and quantify them. They may not have heard about super-ideal branded diamonds or even the AGS (especially in Australia where we rarely see an AGS certificate in a B&M store ... where I live anyway). They may not have even seen a VG compared to an excellent diamond, a shallow vs a deep... or the intricate differences between different proportion sets/symmetry/minor facet interactions.

If the best, super ideal cut diamond in the world was 'x' percentile of diamonds, I still don't know what range the GIA excellent encompasses.

To quote Strmrdr:
"I hear ya Garry...


To be honest the more I learn about the cut grading systems the less I like them GIA more so than AGS.
Why?
For the simple reason that Iv walked into jewelery stores and have been told that GIA EX cut and AGS0 cut is the best in the world and that all of them are just the greatest/best/most awesome.
We know that isn't true."

So how do consumers make a decision? They read the certificates. They may look at a diamond (and have no idea what they're doing whilst the jeweller amuses themselves watching). What I am also trying to say is that consumers place an emphasis on the 'certificate' in front of them. They value the jeweller's opinion but they trust the certificate as the final authority. Whether it's right or not. A consumer isn't an appraiser - they rarely have the skills, experience or equipment to make an informed decision of a diamond's quality by purely looking at it and thus rely on that little piece of paper that says 'AGS 0' or 'GIA excellent'.

e.g. a jeweller could tell a layman a 'good' GIA grading is well ... 'good' and thus it's a 'good' diamond. Or tell the layman it's an 'excellent' diamond. When making this comment, would you expect the jeweller to point to the diamond or the corresponding statement on the certificate? There was a thread on B&M horror stories and fibs not too long ago :razz:

Jewellers can either believe the lab cut grade and price their diamonds accordingly, or don't believe the lab (because they know better or otherwise) but still price their diamonds accordingly. A GIA triple excellent or AGS 0 will be priced higher than a GIA 'good/VG' because consumers will pay the extra for it.
A little bit off topic ... but I will be interested in how this discussion of GIA (or other) cut grades turn out. They 'do' have an impact on consumer purchasing and diamond pricing.

Will a laboratory one day come up with a standardised, reproducible and validated study to which a diamond's grading can be derived from?

Perhaps GIA should add a disclaimer next to their cut grading that reflects the opinions of the Cut Group?

Hmmmms.....
 

Adylon

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I really enjoyed reading this letter and the GIA''s response. It seems to me they''re trying to walk that fine line of being "politically correct" and not too strict while also raising the bar for cut at the same time. I see what the GIA has done as positive overall but I think they can still do better.

Anyhow thank you for posting this :)
 

Garry H (Cut Nut)

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Date: 2/26/2007 10:44:05 AM
Author: JohnQuixote

Date: 2/24/2007 5:01:49 PM
Author: adamasgem
Geeze.. I thought that we covered the five(GIA) versus 11 grade(AGS) math before here on Pricescope.

And clearly showed the argument doesn''t work. Let alone the loosening of other ''standards'' by GIA..

Don Q.. do you have the link??

I note with humor the comment regarding FarceWare(TM) sales in a downward spiral.
Don Corleone.. here it is.


https://www.pricescope.com/community/threads/ags-and-gia-cut-comparison-charts.41793/

Re. comparisons: AGS does not publish parametric ''charts,'' they provide guidelines for manufacture & results may vary depending on the particulars of all 57 facets. I gave an overview 4 posts down on this page for any interested (that conversation grew legs for a plethora of different reasons). So, the above is good for width-of-range comparisons but not border-grades.

Going further; when looking at overall cut grade AGS only considers ''Ideal'' finish. GIA allows EX and VG, which is logical since there is no difference between them to normal human vision.
It appears that some of this difference in grades might have pisappeared as the top AGS grade is in the process of becoming a little wider as discussed in a concurrent thread https://www.pricescope.com/community/threads/ags-2-or-ags-0-the-candidate-vs-parametric-grades.58088/page-6 (this thread is very long and complex - good bed time reading).

However the very bad matches we listed are still likely to occur.
 

adamasgem

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Date: 2/26/2007 10:44:05 AM
Author: JohnQuixote

Don Corleone.. here it is.


https://www.pricescope.com/community/threads/ags-and-gia-cut-comparison-charts.41793/

Re. comparisons: AGS does not publish parametric ''charts,'' they provide guidelines for manufacture & results may vary depending on the particulars of all 57 facets. I gave an overview 4 posts down on this page for any interested (that conversation grew legs for a plethora of different reasons). So, the above is good for width-of-range comparisons but not border-grades.

Going further; when looking at overall cut grade AGS only considers ''Ideal'' finish. GIA allows EX and VG, which is logical since there is no difference between them to normal human vision. One of the only things in the GIA grading system I have sympathy for! Polish is probably over dinged in the AGS and overrated as a critical aspect overall.
 

He Scores

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I wholeheartedly agree with Marty about finish. It''s overated and it should just be a comment on the cert and not part of the cut grade itself. The finish is often out of the control of the cutter due to the material being worked with.

It''s understandable that AGS "overdings" it because they were lobbied by some of the premium manufacturers who sat on their cut research committee and had an interest in having the finish included in the grading. Since these premium manufacturers only work with premium rough, the addition of finish to the grade gave them an advantage over other cutters who cut all material.


Bill
 

diagem

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Date: 2/27/2007 7:46:41 PM
Author: He Scores


I wholeheartedly agree with Marty about finish. It''s overated and it should just be a comment on the cert and not part of the cut grade itself. The finish is often out of the control of the cutter due to the material being worked with.

It''s understandable that AGS ''overdings'' it because they were lobbied by some of the premium manufacturers who sat on their cut research committee and had an interest in having the finish included in the grading. Since these premium manufacturers only work with premium rough, the addition of finish to the grade gave them an advantage over other cutters who cut all material.


Bill
On one aspect... manufacturers/vendors turns to the AGS reports for the highest (perfect) cut grades on round Diamonds!!!
And many here are considering AGS reports as the authority when it comes to "ideal" rounds...

Its true, the polish/finish of a Diamond is sometimes out of the cutters control!!! So are other characteristics!!!

If manufacturers/vendors are using the AGS system to market "perfectly" cut round Diamonds..., then if the Diamond is not perfectly polished..., it should not fit that "perfect" AGS category! Sorry, no excuses!!!

Since the large majority of rough (used by Diamond manufacturers worldwide) is not considered "premium", I can''t imagine a professional lab. as the AGS allowing its grading decisions/parameters being influenced by a "so called" lobby of premium manufacturers!!!

Bill, it just does not add-up!
 

adamasgem

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Date: 2/27/2007 7:46:41 PM
Author: He Scores


I wholeheartedly agree with Marty about finish. It''s overated and it should just be a comment on the cert and not part of the cut grade itself. The finish is often out of the control of the cutter due to the material being worked with.

It''s understandable that AGS ''overdings'' it because they were lobbied by some of the premium manufacturers who sat on their cut research committee and had an interest in having the finish included in the grading. Since these premium manufacturers only work with premium rough, the addition of finish to the grade gave them an advantage over other cutters who cut all material.


Bill
Bill, my objection is that, as you say, sometimes a small pavilion facet (or other) won''t take a perfect polish, and that one facet downgrades the stone way out of proportion to the effect on performance. Giving it equal "weight" with the make and fashioning of the stone seems unreasonable.

As to the reason you state, supply and type of rough, or lobbying you allude to, so to speak, I have not a clue on the historical "reasons".

And while suoer ideal symmetry doesn''t receive any deductions, or downgrades for light performance, it doesn''t seem to receive the rewards it deserves also, either by GIA or AGS. AGS seems much tighter on this than GIA, to the extent of where the thresholds have been set.
 

adamasgem

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Date: 2/28/2007 3:17:06 AM
Author: DiaGem

If manufacturers/vendors are using the AGS system to market ''perfectly'' cut round Diamonds..., then if the Diamond is not perfectly polished..., it should not fit that ''perfect'' AGS category! Sorry, no excuses!!!
I would liken it toward the idea of a baseball analogy, there are the major and minor leagues and then there are the majority of the sandlot players in the world who will never make it to either. And there is no World Series...
 

Garry H (Cut Nut)

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Date: 2/28/2007 5:45:28 AM
Author: adamasgem

Date: 2/28/2007 3:17:06 AM
Author: DiaGem

If manufacturers/vendors are using the AGS system to market ''perfectly'' cut round Diamonds..., then if the Diamond is not perfectly polished..., it should not fit that ''perfect'' AGS category! Sorry, no excuses!!!
I would liken it toward the idea of a baseball analogy, there are the major and minor leagues and then there are the majority of the sandlot players in the world who will never make it to either. And there is no World Series...
People outside USA sometimes wonder why you call it the world series?

GIA certainly has a more reasonable approach to plolish and sym - an Excellent cut for proportions VG VG will not fetch as much as an EX EX EX, so there is no need to doubly penalise as AGS do in my opinion.

I also prefer certain aspect of GIA''s approach such as girdle thickness - especially now that AGS is making a push for larger stones. A 3ct with AGS''s maximum girdle thickness is too thick in my book - I like the GIA method where the thickness is relative to the size of the diamond.

Any issues that anyone has picked up in the 2 letters?
Surely there are some contentious pints - or is all too hard to read? Good sleep inducer?
 

strmrdr

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Date: 2/28/2007 12:16:01 PM
Author: Garry H (Cut Nut)
Any issues that anyone has picked up in the 2 letters?
Surely there are some contentious pints - or is all too hard to read? Good sleep inducer?
Sure but do you want to really hear it again?

1st: DD stuff is a red herring. The DD isnt in my opinion why the system is bad.
2nd: Rounding flat out sux and I would hammer that point.
3rd: too much trade involvement and not enough consumer viewing
4th: Id like GIA''s answer on the statement: "the GIA grading system is a system for the trade by the trade" and hear what their defense is.
 

adamasgem

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Date: 2/28/2007 12:16:01 PM
Author: Garry H (Cut Nut)

Date: 2/28/2007 5:45:28 AM
Author: adamasgem


Date: 2/28/2007 3:17:06 AM
Author: DiaGem

If manufacturers/vendors are using the AGS system to market ''perfectly'' cut round Diamonds..., then if the Diamond is not perfectly polished..., it should not fit that ''perfect'' AGS category! Sorry, no excuses!!!
I would liken it toward the idea of a baseball analogy, there are the major and minor leagues and then there are the majority of the sandlot players in the world who will never make it to either. And there is no World Series...
People outside USA sometimes wonder why you call it the world series? I agree
The little world series is better represented, however the major leagues in the US are well represented by the best players in the world.


GIA certainly has a more reasonable approach to plolish and sym - an Excellent cut for proportions VG VG will not fetch as much as an EX EX EX, so there is no need to doubly penalise as AGS do in my opinion.
AGS has historically been stricter in all aspects of grading.

I also prefer certain aspect of GIA''s approach such as girdle thickness - especially now that AGS is making a push for larger stones. A 3ct with AGS''s maximum girdle thickness is too thick in my book - I like the GIA method where the thickness is relative to the size of the diamond. What they publisize (teach) and what they do in the lab have been two different things in the past, and they keep bumping up the min maxs for a subjective girdle thickness grade. We''ve discussed this on PS before..

Any issues that anyone has picked up in the 2 letters? Needless to say, as Storm says "their rounding sux"
As does their face up only brilliance model..More when I get the time..


Surely there are some contentious pints - or is all too hard to read? Good sleep inducer? ZZZZZZZZZZZZZ
 

adamasgem

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RE: First, as stated in reference iv (again, the Fall 2004 issue of Gems & Gemology), we knew the system needed more than just brightness and fire metrics because those two factors alone gave an agreement rate of only 58% ; in contrast, the finished GIA cut grading system for RBCs showed 92% agreement between human observations of overall appearance and system assignment of grades – the same agreement rate the observers showed with each other. We would also like to emphasize that much of our observation testing was devoted to "overall appearance" and not just to brightness and fire as stated."

Easy to get same % agreement when all you have to do is use (or add) the "taste test" results.
 

adamasgem

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Date: 2/28/2007 12:16:01 PM
Author: Garry H (Cut Nut)

Date: 2/28/2007 5:45:28 AM
Author: adamasgem


Date: 2/28/2007 3:17:06 AM
Author: DiaGem

If manufacturers/vendors are using the AGS system to market ''perfectly'' cut round Diamonds..., then if the Diamond is not perfectly polished..., it should not fit that ''perfect'' AGS category! Sorry, no excuses!!!
I would liken it toward the idea of a baseball analogy, there are the major and minor leagues and then there are the majority of the sandlot players in the world who will never make it to either. And there is no World Series...
People outside USA sometimes wonder why you call it the world series?
Garry, Sidenote:

I had a longer post, and more detailed post, but I screwed it up , and lost it. I grew up in AAA baseball.

Perhaps you could check the BaseBall Hall of Fame for my father''s name of the owner of the Syracuse Chiefs. a mid 1950''s Govenor''s Cup Winner (one step below the world Series). I can even relate stories told to me by my father and uncle, about the Havana Sugar Kings, who were members of the league we beat the pants off..

I grew up with professional sports, including what is now an NBA team..

I''ve had the honor, of having in my hoe. and meeting elsewhere, in my precocious yiouth, some of the historical greats, Cy Young Award winners, World Series Managers, NBA historical figures (my dad had part orf the predesor to the Phily 76''s, the Syracuse Nationals, and as a kid, meeting the biiggest hands I''ve ever seen, Rocky Marciano.


Historical record, my friend, and not like the paddle ball called Crciket, you guys try to play down under
 

Garry H (Cut Nut)

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Date: 2/28/2007 1:21:56 PM
Author: strmrdr

Date: 2/28/2007 12:16:01 PM
Author: Garry H (Cut Nut)
Any issues that anyone has picked up in the 2 letters?
Surely there are some contentious pints - or is all too hard to read? Good sleep inducer?
Sure but do you want to really hear it again?

1st: DD stuff is a red herring. The DD isnt in my opinion why the system is bad.
2nd: Rounding flat out sux and I would hammer that point.
3rd: too much trade involvement and not enough consumer viewing
4th: Id like GIA''s answer on the statement: ''the GIA grading system is a system for the trade by the trade'' and hear what their defense is.
Storm I had a limited amount of time with DD 2 days ago, and it is very clear that the viewing position they used does bias toward deeper stones.

And princess look brighter or at least as bright as rounds with fluoro light on, where as rounds always look brighter with the light off.

Have a good look at Sergey''s ETAs images for the same 3 stones in my earlier studies.

3. agreed

2. GIA-GTL - the lab apparently do not round in their lab grading.
 

Garry H (Cut Nut)

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Date: 2/28/2007 2:35:14 PM
Author: adamasgem
RE: First, as stated in reference iv (again, the Fall 2004 issue of Gems & Gemology), we knew the system needed more than just brightness and fire metrics because those two factors alone gave an agreement rate of only 58% ; in contrast, the finished GIA cut grading system for RBCs showed 92% agreement between human observations of overall appearance and system assignment of grades – the same agreement rate the observers showed with each other. We would also like to emphasize that much of our observation testing was devoted to ''overall appearance'' and not just to brightness and fire as stated.''

Easy to get same % agreement when all you have to do is use (or add) the ''taste test'' results.
If anyone with a stats background would like to wade through GIA''s Founation article (27 pages in total) the relevant pages are about 214 to 220. For the life of me it seems to be an obscuration rather than an explanation.
Here is the online publication http://www.gia.edu/pdfs/cut_fall2004.pdf
 

Londonchris

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Just to add abit of useless info
i have moved home and business to a location not more than 20 mins bus trip from Sergey in Finland.
Small world.
 

Garry H (Cut Nut)

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Date: 2/28/2007 1:21:56 PM
Author: strmrdr

1st: DD stuff is a red herring. The DD isnt in my opinion why the system is bad.
Storm I have had a small window of opportunity to do some testing inside Diamond Dock.

I used 2 princess cuts chosen at random and one shallow ish round that I happened to have with me.

The photo''s on the top row have the fluoro only lights on and are taken at about 40 - 45 dgerees between the stones and the light center point (the viewing angle that I believe was used in the GIA survey to set the proportion grades).

I think you would agree that had I found better examples of princess cuts (I had already bought the best ones and they were packed away) then this grading environment would favour princess cuts over rounds. i.e. princess cuts would be morre ideal than ideal cut rounds!

The lower photo''s are a bit fuzzy because they were taken with the lights off and I had some camera shake because the exposure time was longer.
In fact you very clearly see the round stone is far brighter with just the ambient room light - and this is the normal situation.

I fail to see how a grading environment that gets such a fundemental difference wrong can be used as the basis of a multi billion dollar decision making process.

Is this a red herring?

Feb 2007 DD photos princess and round.JPG
 

Garry H (Cut Nut)

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Date: 2/28/2007 8:13:46 PM
Author: adamasgem

Date: 2/28/2007 12:16:01 PM
Author: Garry H (Cut Nut)


Date: 2/28/2007 5:45:28 AM
Author: adamasgem



Date: 2/28/2007 3:17:06 AM
Author: DiaGem

If manufacturers/vendors are using the AGS system to market ''perfectly'' cut round Diamonds..., then if the Diamond is not perfectly polished..., it should not fit that ''perfect'' AGS category! Sorry, no excuses!!!
I would liken it toward the idea of a baseball analogy, there are the major and minor leagues and then there are the majority of the sandlot players in the world who will never make it to either. And there is no World Series...
People outside USA sometimes wonder why you call it the world series?
Garry, Sidenote:

I had a longer post, and more detailed post, but I screwed it up , and lost it. I grew up in AAA baseball.

Perhaps you could check the BaseBall Hall of Fame for my father''s name of the owner of the Syracuse Chiefs. a mid 1950''s Govenor''s Cup Winner (one step below the world Series). I can even relate stories told to me by my father and uncle, about the Havana Sugar Kings, who were members of the league we beat the pants off..

I grew up with professional sports, including what is now an NBA team..

I''ve had the honor, of having in my hoe. and meeting elsewhere, in my precocious yiouth, some of the historical greats, Cy Young Award winners, World Series Managers, NBA historical figures (my dad had part orf the predesor to the Phily 76''s, the Syracuse Nationals, and as a kid, meeting the biiggest hands I''ve ever seen, Rocky Marciano.


Historical record, my friend, and not like the paddle ball called Crciket, you guys try to play down under
An interesting way to grow up surrounded by stars - no wonder you have been a high achiever :)
Even further off topic Marty.
I was getting into an elevator the other day and all these guys in blue T shirts walked up - mostly Indian looking - some got in my lift. I was right next to a short Indian and a tall (aussie by his accent) guy - i asked him what the ''Sahara'' on their T shirts stood for. He said it is a Indian company - I said - you must be here for a buisness training seminar? He said - no we are a cricket team - I asked which one, and he said the Indian team. I said they looked a bit young for that?

They got out and another person in the elevator (an American) said that little guy next to you is Sachin Tandulka. He is the most famous ever. Next morning watching the news, the Indian cricket team were being interviewed as they left the country for a match in the Caribean. I relaized the guy I was talking to was Greg Chappel - the ex Aussie Captain and star who now coaches the Indian team.

So that is how much notice I take of sport and sportsmen :(
(Some of my Aussie mates have disowned me)
 

diagem

Ideal_Rock
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Messages
4,936
Date: 3/1/2007 3:07:26 AM
Author: Garry H (Cut Nut)

Date: 2/28/2007 1:21:56 PM
Author: strmrdr

1st: DD stuff is a red herring. The DD isnt in my opinion why the system is bad.
Storm I have had a small window of opportunity to do some testing inside Diamond Dock.

I used 2 princess cuts chosen at random and one shallow ish round that I happened to have with me.

The photo''s on the top row have the fluoro only lights on and are taken at about 40 - 45 dgerees between the stones and the light center point (the viewing angle that I believe was used in the GIA survey to set the proportion grades).

I think you would agree that had I found better examples of princess cuts (I had already bought the best ones and they were packed away) then this grading environment would favour princess cuts over rounds. i.e. princess cuts would be morre ideal than ideal cut rounds! Why, because they (princesses) are brighter?
I still think the round has what the GIA calls "Positive Pattern" (as in figure B- 1).


The lower photo''s are a bit fuzzy because they were taken with the lights off and I had some camera shake because the exposure time was longer.
In fact you very clearly see the round stone is far brighter with just the ambient room light - and this is the normal situation. Depends on the kind of lighting, angle of view, and obstructions nearby, the "positive or negative pattern" can be noticed even in ambient room light..., don''t you agree?

I fail to see how a grading environment that gets such a fundemental difference wrong can be used as the basis of a multi billion dollar decision making process.I agree with you on that one..., but someone has to define a grading environment..., would you base a grading environment only on "Natural Northern daylight"?

Is this a red herring?
Garry,
GIA wrote on page 218:

Thus, given the interdependence of flashing
light and distribution, we decided to use two terms
to represent these different aspects of scintillation.
Sparkle describes the spots of light seen in a polished
diamond when viewed face-up that flash as
the diamond, observer, or light source moves.
Pattern is the relative size, arrangement, and contrast
of bright and dark areas that result from internal
and external reflections seen in a polished diamond
when viewed face-up while that diamond is
still or moving. As such, patterns can be seen as
positive (balanced and cohesive patterns; see figure
B-1) or negative (e.g., fisheyes, dark centers, or irregular
patterns; see figure B-2).

It makes perfectly sense to me!!!

BTW, I would go for the round and not for the princesses in that first row of yours!
 

Garry H (Cut Nut)

Super_Ideal_Rock
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Joined
Aug 15, 2000
Messages
15,202
Date: 3/1/2007 5:11:08 AM
Author: DiaGem

Date: 3/1/2007 3:07:26 AM
Author: Garry H (Cut Nut)


Date: 2/28/2007 1:21:56 PM
Author: strmrdr

1st: DD stuff is a red herring. The DD isnt in my opinion why the system is bad.
Storm I have had a small window of opportunity to do some testing inside Diamond Dock.

I used 2 princess cuts chosen at random and one shallow ish round that I happened to have with me.

The photo''s on the top row have the fluoro only lights on and are taken at about 40 - 45 dgerees between the stones and the light center point (the viewing angle that I believe was used in the GIA survey to set the proportion grades).

I think you would agree that had I found better examples of princess cuts (I had already bought the best ones and they were packed away) then this grading environment would favour princess cuts over rounds. i.e. princess cuts would be morre ideal than ideal cut rounds! Why, because they (princesses) are brighter? No - these princess cuts are not even close to brighter other than when you see them in DD.
I still think the round has what the GIA calls ''Positive Pattern'' (as in figure B- 1). DD was not used to discover pattern - they used salad bowls for that.

The lower photo''s are a bit fuzzy because they were taken with the lights off and I had some camera shake because the exposure time was longer.
In fact you very clearly see the round stone is far brighter with just the ambient room light - and this is the normal situation. Depends on the kind of lighting, angle of view, and obstructions nearby, the ''positive or negative pattern'' can be noticed even in ambient room light..., don''t you agree? Of course - but they were using DD with fluoro''s for brightness. If bad patterns were noticed then this could become part of their so called ''scintillation'' study, but they have not shown any evidence of quantification in their very long article.

I fail to see how a grading environment that gets such a fundemental difference wrong can be used as the basis of a multi billion dollar decision making process.I agree with you on that one..., but someone has to define a grading environment..., would you base a grading environment only on ''Natural Northern daylight''? I do not have an answer - it depends on the type of jewellery and the type of buyer / owner / user. e.g. an evening piece should have different grading lighting than an engagement ring.

Is this a red herring?
Garry,
GIA wrote on page 218:

Thus, given the interdependence of flashing
light and distribution, we decided to use two terms
to represent these different aspects of scintillation.
Sparkle describes the spots of light seen in a polished
diamond when viewed face-up that flash as
the diamond, observer, or light source moves.
Pattern is the relative size, arrangement, and contrast
of bright and dark areas that result from internal
and external reflections seen in a polished diamond
when viewed face-up while that diamond is
still or moving. As such, patterns can be seen as
positive (balanced and cohesive patterns; see figure
B-1) or negative (e.g., fisheyes, dark centers, or irregular
patterns; see figure B-2). They are nice words - but there is no metric or quantification. And that was our point in both the original article and the exchange of letters. They quoted %''s of match of computer derived metrics and observation results and used the nice words above to explain why there was only a 58% match.

It makes perfectly sense to me!!!

BTW, I would go for the round and not for the princesses in that first row of yours!
 

diagem

Ideal_Rock
Trade
Joined
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Messages
4,936
Just came back from testing the DD..., Garry, you are right, it complimented (big-Time) out-of-the-ordinary fancy cuts that I used for testing vs. regular fluo. light used in Diamond/Industry offices.
Its not the "ideal" light environment for grading Diamond face-up appearances!!!
I did notice It would be a good tool to observe Diamond pattern!!!

I think (not 100% sure yet) I noticed that on off-colored Diamonds the DD brings out the better (artificial) face-up appearance that it would show in "ambient room lighting"!!! Am I making sense here?

And now for the bad news (unless i am used to my own lighting environment), I think it is definitely the wrong tool-box to determine/grade a color for D-Z graded colored Diamonds. I may be wrong..., but that is what i picked up after a rather quick test!!!!

And I would be surprised to hear that GIA grades Fancy-Colored Diamonds on DD, especialy when these Diamonds are only graded faced-up!!!!!!!!
 
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