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GIA Excellent Cut vs. Very good cut?

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nvshelat

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Is it possible to tell the difference between two diamonds:
(1) GIA excellent polish and excellent symetry but very good cut
(2) GIA excellent polish and excellent symetry and excellent cut

with the naked eye? In terms of their light return, brilliance, etc? I haven''t been able to scrounge up a picture of the two side by side - GOG only has excellent and good side by side, where you can definately tell the difference..
 

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DBM

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IMO i would venture to say no. Most people cannot. I wonder if Garry Holloway ever conducted an experiment with that...
 

Regular Guy

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The question assumes a buy in to the usefulness of the descriptors. The argument on Pricescope goes that comparing the two is something like saying...is a child predictably shorter than an adult. In the same way that HCA associations with VG for GIA are sometimes more favorable than they are for excellent...likewise, clearly, some teenagers are taller than some adults. The implication is that the categories from GIA are, while designed to be "inclusive" of many tastes, do not describe sufficiently tight a high quality range to be helpful for someone committed to finding only a high quality range. So, GIA with 5 levels may not be as helpful in this regard as AGS with 11 levels, for example...whether or not there is even an agreement within the GIA levels, which there is not.
 

oldminer

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GIA''s excellent grade is so wide that by the time you get to very good I believe one might see some minor variation in performance. It won''t be overwhelming, but excellent covers a lot of territory in the new system. Some experts may agree excellent is overly generous. Diamond dealers will more likely like the liberal nature of the system. There is no industry wide consenus as yet.
 

Rhino

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Date: 12/29/2006 11:07:11 AM
Author:nvshelat
Is it possible to tell the difference between two diamonds:
(1) GIA excellent polish and excellent symetry but very good cut
(2) GIA excellent polish and excellent symetry and excellent cut

with the naked eye? In terms of their light return, brilliance, etc? I haven't been able to scrounge up a picture of the two side by side - GOG only has excellent and good side by side, where you can definately tell the difference..
Hi nv,

Yes definitely. There are some "very good" combos I would consider better than others however there is a visual difference from the "excellent" cut grades to the "very goods". While GIA does look at weight ratio and durability issues in determining a cut grade there are 4 alterations in proportions that skew diamond appearance. Those 4 being ...

1. steep angled combinations.
2. shallow angled combinations
3. painting of girdle facets
4. digging of the girdle facets

The steep angled combinations contribute to leakage which is visible and causes a diamond to take on a watery/glassy appearance.
The shallow angled combinations contribute to increased darkness in the diamond. At first notable in the pavilion mains then progressing to increased darkness under the table.
Once painting reaches a certain threshold it increases darkness at first around the perimeter then progresses to under the table.
Same with digging.

Not all "excellents" however take on the same appearance. I've found steep angled combos wherein the leakage was discernable so I have established certain cut off's personally that I will not purchase or encourage.

Peace,
 

belle

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Date: 12/29/2006 11:07:11 AM
Author:nvshelat
Is it possible to tell the difference between two diamonds:
(1) GIA excellent polish and excellent symetry but very good cut
(2) GIA excellent polish and excellent symetry and excellent cut

with the naked eye? In terms of their light return, brilliance, etc? I haven't been able to scrounge up a picture of the two side by side - GOG only has excellent and good side by side, where you can definately tell the difference..
there are too many variables to make such a decisive conclusion. none of the examples you gave (polish/symmetry/cut grade alone) are enough to determine that one would be better than another. especially relating to light return, brillliance, etc. i have a diamond that was dinged...er...graded
'very good' by gia and it is truly spectacular. there is nothing inferior about it. unfortunately, the highest grade a diamond with a 'thin' girdle can get from gia is only 'very good'.
so, that means my amazing sparkler is only 'papered' as 'very good' because of the 'thin' (which i love!) girdle, even though it puts the majority of diamonds out there to shame.
it just goes to show that you need to get more info before you decide.
 

Rhino

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Date: 12/29/2006 1:12:32 PM
Author: belle

Date: 12/29/2006 11:07:11 AM
Author:nvshelat
Is it possible to tell the difference between two diamonds:
(1) GIA excellent polish and excellent symetry but very good cut
(2) GIA excellent polish and excellent symetry and excellent cut

with the naked eye? In terms of their light return, brilliance, etc? I haven''t been able to scrounge up a picture of the two side by side - GOG only has excellent and good side by side, where you can definately tell the difference..
there are too many variables to make such a decisive conclusion. none of the examples you gave (polish/symmetry/cut grade alone) are enough to determine that one would be better than another. especially relating to light return, brillliance, etc. i have a diamond that was dinged...er...graded
''very good'' by gia and it is truly spectacular. there is nothing inferior about it. unfortunately, the highest grade a diamond with a ''thin'' girdle can get from gia is only ''very good''.
so, that means my amazing sparkler is only ''papered'' as ''very good'' because of the ''thin'' (which i love!) girdle, even though it puts the majority of diamonds out there to shame.
it just goes to show that you need to get more info before you decide.
Hi belle,

Something doesn''t make sense.
There are many diamonds that are Ex that have "thin" girdles or "thin - medium". Are you sure that''s the reason your stone got VG? Curious.

Also ... Happy New Year to ya.
 

belle

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of course, now i can''t find where i saw that about the highest grade being ''very good'' on thin girdles.
obviously, you have seen examples of them and alj pointed another out so it seems it can happen. i will continue to search for whatever it was that got that into my mind. perhaps it is nothing more than outdated information.

i still unequivocally contend that you cannot make categoric judgements about definite differences in gia cut grades without knowing more. you can make general judgements but most certainly not definite.
 

belle

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in fact rhino it’s technically depth according to facetware but it''s just stupid to say a 60.6 depth will result in ''very good''

if you look at the image below, diamond 1 is mine. you can see the comment at the bottom of the graphic…although the girdle min and max say thin-thin on diamonds 1 and 2 you can see in the little diamond drawings that they build the depth difference from 60.6 which is ''very good'', to a 60.7 which is ''excellent'' into the girdle
crazy? i think so.


mydiamondsgirdle.jpg
 

tanalasta

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Interesting. So what would happen to all the previously 'excellent' grades that would then be classed as 'very good'?
 

kenny

Super_Ideal_Rock
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So Garry, where do you feel the GIA first went wrong?
 

Garry H (Cut Nut)

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It is hard to say Kenny.

They made the worst mistakes in their Fire study, but they really messed up with Diamond Dock - an attempt to make a common viewing lighting environmnet.

Read all about it in the topic near the top of the FAQ section and a journal article.

Our Cut Group have responded to a letter to the editor that was sent by the GIA to the Australian Gemmologist Journal. It is the first open and public chance we had to interact with the GIA Cut Study team. I can not publish the contnents of their letter or our response until it is released in the journal. A lot will become apparent after that.
 

aljdewey

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Date: 12/29/2006 7:57:48 PM
Author: Garry H (Cut Nut)
It is hard to say Kenny.

They made the worst mistakes in their Fire study, but they really messed up with Diamond Dock - an attempt to make a common viewing lighting environmnet.
OHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH.

I feel a "Rainman" attack coming on! Banging head on the keyboard now.
 

aljdewey

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g-a-r-r-y. My main man.

diamond dock rainman.JPG
 

mrssalvo

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LOL.. AL, you are in rare form this evening, too funny!!!
 

aljdewey

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*SOB* I can''t help it!

I''m hitting Dee''s $100 wine!

HEHEHEHEHEE
 

mrssalvo

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well i''m not even drinking tonight and am rolling with laughter so i can just imagine how funny things are for those partaking..
 

Garry H (Cut Nut)

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Date: 12/29/2006 9:51:24 PM
Author: aljdewey

Date: 12/29/2006 7:57:48 PM
Author: Garry H (Cut Nut)
It is hard to say Kenny.

They made the worst mistakes in their Fire study, but they really messed up with Diamond Dock - an attempt to make a common viewing lighting environmnet.
OHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH.

I feel a ''Rainman'' attack coming on! Banging head on the keyboard now.
Oh Aldj - you are as good as me at getting into trouble!!!

(BTW - i fly Quantas too]
 

lumpkin

Ideal_Rock
Joined
May 24, 2005
Messages
2,491
I'm absolutely no expert. I have a "very good" GIA cut and it would have gotten an "excellent" but for the very thin to med girdle. It scored very well on the HCA -- I can't remember exactly the score, but WELL under 2.0. I know there are more excellently cut diamonds out there, but for some reason it doesn't bother me at all. I LOVE my diamond. It sparkles like crazy. I highly recommend the Holloway Cut Advisor to weed out diamonds you do not want to look at.

I'm really biased away from stones that have such a distinct hearts and arrows pattern that it's the first thing I see when I look at the diamond. Other people really relish that pattern and want to be able to see it immediately in their diamond. A GIA excellent doesn't guarantee a perfect H & A pattern if that is important to you. All H & A patterns are not the same, visually, either -- some have short, fat, dark arrows and some have longer, slender, more subtle arrows (my preference) and you can't depend on the report to tell you exactly what the diamond will look like. You will still have to see it and compare it to others. I think you are just going to have to research all the information available and decide for yourself what is acceptable to you on paper and then just look at the diamonds to make your decision. It's a very fun quest!
 

Rhino

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Hi belle,


Date: 12/29/2006 4:53:19 PM
Author: belle
of course, now i can''t find where i saw that about the highest grade being ''very good'' on thin girdles.
obviously, you have seen examples of them and alj pointed another out so it seems it can happen. i will continue to search for whatever it was that got that into my mind. perhaps it is nothing more than outdated information.
Not really. Thin girdles have always been fine in both GIA and AGS systems. I do find that both labs do look at slightly different factors when it comes to girdle analysis. Namelly GIA bases the grade on a physical exam while AGS looks at the numbers produced by the scan of the girdle as well as a physical. I''ve had stones that didn''t get GIA Ex because of it yet make AGS Ideal.


i still unequivocally contend that you cannot make categoric judgements about definite differences in gia cut grades without knowing more. you can make general judgements but most certainly not definite.
I agree that each diamond can take on different characteristics but once you look at enough stones that get the VG grade for one of the 4 reasons stated above (steep/shallow/painting/digging) you get to the point when you can look at a diamond and see what it was that caused the VG grade. This only comes with experience though and seeing enough of them to familiarize yourself with what to expect. When folks come to our store we show, upon request, the varying appearances that cause the decrease in brightness and hence the VG grade. Rarely when we show these comparisons does a person disagree with the GIA grade. Of course I show them what I consider to be the best amongst the GIA grades but with enough viewing and experience any person can see and learn.

It''s akin to how bank tellers are trained to detect counterfeits. My wife used to work in a bank and the way they''d train them was to put in their hands the real McCoy hundreds to thousands of times. The real McCoy has a certain feel. A certain texture. A certain look. Once a counterfeit is in the hands of an experienced teller they can tell immediately even if they can''t put their finger exactly on why its counterfeit.

Same with diamonds. I am at a little bit of an advantage though since I am in the trade hence I get to see scores of diamonds that you don''t. If you''re ever up this way I''ll be happy to show ya.

Peace,
 

Rhino

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Date: 12/29/2006 5:05:03 PM
Author: belle

in fact rhino it’s technically depth according to facetware but it''s just stupid to say a 60.6 depth will result in ''very good''

if you look at the image below, diamond 1 is mine. you can see the comment at the bottom of the graphic…although the girdle min and max say thin-thin on diamonds 1 and 2 you can see in the little diamond drawings that they build the depth difference from 60.6 which is ''very good'', to a 60.7 which is ''excellent'' into the girdle
crazy? i think so.
LOL... yes.
In fact ... just as crazy as giving as giving a diamond a "very good" spread instead of an "excellent" one becuase of a depth % of 60.4% instead of 60.3%.


Actually its not necessarily the depth causing the VG grade in the FW estimator although it relates to it. Here''s the breakdown for clarification.

When you input those measurements into the FW using that total depth it is estimating the girdle thickness at the bezels to be 2.0%. You can see that grayed out in the graphic you posted. In the new GIA system GIA now not only looks at the girdle thickness in the valley''s but also the girdle thickness at the bezels. The girdle thickness at the bezels must be a minimum of 2.5% (in reality can be 2.256% at the very least and rounded). So what is causing the VG grade on the FW estimator in the example you provided isn''t the depth perse but the girdle thickness at the bezels. The FW estimator is estimating the girdle thickness to be at 2.0% with the measurements and depth you provided.

This raises the question...

How important is girdle thickness at the bezels? That''s an entirely different discussion because in my mind the girdle thickness at the valley''s is the most important place to look on the diamond becuase that is the thinnest portion which is most succeptible to chipping. If the girdle thickness at the valley''s is fine (and "thin" is perfectly fine) why would a girdle thickness of 2.0% at the bezels NOT be fine?

Any other pro reading have an opinion or answer? I''ll pose it to some contacts and see what they say.
 

Rhino

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Date: 12/29/2006 7:34:57 PM
Author: Garry H (Cut Nut)
I imagine 2007 will be the year of the gIA rethink of its grading system.

This will cause havoc in the market and they will continue to need a lawyer as a CEO.
Heresay or fact? I don''t see any reason for them to change what they have? Perhaps tweaks here and there but a complete rethink? I highly doubt it Garry.
 

Rhino

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Date: 12/29/2006 9:51:24 PM
Author: aljdewey

Date: 12/29/2006 7:57:48 PM
Author: Garry H (Cut Nut)
It is hard to say Kenny.

They made the worst mistakes in their Fire study, but they really messed up with Diamond Dock - an attempt to make a common viewing lighting environmnet.
OHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH.

I feel a ''Rainman'' attack coming on! Banging head on the keyboard now.


For the record I''ve been using the DiamondDock 5 days a week for about a year now and find no discrepancy between the assessment it shows vs the most natural diffuse lighting environments you can view a diamond in. I have the luxury of being able to examine diamonds with it as well as taking the same exact stones outside in natural diffuse lighting and I am not finding what Garry is claiming here.


My .02c
 

Rhino

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Date: 12/29/2006 10:26:26 PM
Author: mrssalvo
well i''m not even drinking tonight and am rolling with laughter so i can just imagine how funny things are for those partaking..
Now where''s the white zinfandel when I need it! That had me rolling too mrss.
 

Cehrabehra

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Date: 12/30/2006 3:41:24 PM
Author: Rhino

Date: 12/29/2006 9:51:24 PM
Author: aljdewey


Date: 12/29/2006 7:57:48 PM
Author: Garry H (Cut Nut)
It is hard to say Kenny.

They made the worst mistakes in their Fire study, but they really messed up with Diamond Dock - an attempt to make a common viewing lighting environmnet.
OHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH.

I feel a ''Rainman'' attack coming on! Banging head on the keyboard now.


For the record I''ve been using the DiamondDock 5 days a week for about a year now and find no discrepancy between the assessment it shows vs the most natural diffuse lighting environments you can view a diamond in. I have the luxury of being able to examine diamonds with it as well as taking the same exact stones outside in natural diffuse lighting and I am not finding what Garry is claiming here.


My .02c
I don''t like the way the diamonds don''t sit well.... but that''s just my 2cent observation lol
 

Garry H (Cut Nut)

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Date: 12/30/2006 3:41:24 PM
Author: Rhino

Date: 12/29/2006 9:51:24 PM
Author: aljdewey


Date: 12/29/2006 7:57:48 PM
Author: Garry H (Cut Nut)
It is hard to say Kenny.

They made the worst mistakes in their Fire study, but they really messed up with Diamond Dock - an attempt to make a common viewing lighting environmnet.
OHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH.

I feel a ''Rainman'' attack coming on! Banging head on the keyboard now.


For the record I''ve been using the DiamondDock 5 days a week for about a year now and find no discrepancy between the assessment it shows vs the most natural diffuse lighting environments you can view a diamond in. I have the luxury of being able to examine diamonds with it as well as taking the same exact stones outside in natural diffuse lighting and I am not finding what Garry is claiming here.


My .02c
As you well know Rhino - you use it at a completely different angle to what was used in their +70,000 observation survey.

The angle you use it at shows shallow stones appearing as good as Tolkowsky.
The angle they used it at shows slightly deep steep looking as good as Tolkowsky.

The +70,000 data was therefore flawed. And their grading system is based on that survey.
 

belle

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here we are so far:

belle: my stone got 'very good' because of the girdle.

rhino: it doesn’t make sense...are you sure that’s the reason?


belle: well, facetware says it’s depth but it’s actually a thin girdle, see graphic.


rhino: actually, it’s not the depth. it’s the thin girdle, belle.



glad we got that all straightened out!

 

aljdewey

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Joined
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Messages
9,143
Date: 12/31/2006 7:23:12 PM
Author: belle




here we are so far:

belle: my stone got 'very good' because of the girdle.





rhino: it doesn’t make sense...are you sure that’s the reason?






belle: well, facetware says it’s depth but it’s actually a thin girdle, see graphic.






rhino: actually, it’s not the depth. it’s the thin girdle, belle.



glad we got that all straightened out!

Ok - Rainman episode totally replaced......by COUGHING and SPEWING the soda that I WAS drinking normally until I read this!

ROTFLMAO
 
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