Battle of the Charts: GIA Vs AGS

[Houseparty]

Greetings,
I find all of this cut grade controversy fascinating. I am very new to this community, but most everybody seems kind, thoughtful, fun, and even obsessive. I would be very interested how two very different stones would be evaluated. I do not have the knowledge, toys, or the "ice" to help, but the results could be very interesting.

Stone A:
PA 41.8
CA 34.0
GIA chart says "Excellent", no other combination looks discernibly better
AGS chart says, no way that''s a "4"

Stone B:
PA 40.4
CA 36.0
GIA chart says only "Very Good". We have this enormous number of combinations that we consider top grade, but no stone with this tight PA can be "Excellent"
AGS says are you kidding me, out top grade is only one fifth the size of yours. This is a "0", a top rated stone

All other factors would be materially the same and typical. For example, 1 carat, 57 tables, medium girdle, Stars 55, LG 80, etc... The depth % would be the geometric result of the above data (you smart guys know how to do that).

Both labs have substantial reputations and resources beyond compare, but they come up with such different conclusions. Who is right and who is wrong?

Thanks,
David

 

[february2003bride]

In this case I would send the stones to an independant appraiser for a third opinion.

Carrie

 

[strmrdr]

Id pass on the first one and buy the second one.
Its still a diamond by diamond decision just like it always has been.

The cut grades are a filter nothing more.
Some will put more weight in one and some the other.
Some will ignore both.

 

[strmrdr]

Here is the first one:
it scores VG on light return just a tic under the top diamonds.
The contrast is good too but all the contrast is from leakage under the table which is bad.

 

[strmrdr]

here is the gem file for it.

edit: going to redo with a different girdle.
Doesnt change much but want to be fair to your test.

 

[Mara]

eh i wouldnt be interested in either of them.

the interesting and sometimes frustrating thing about all of this diamond stuff is that NO ONE is actually right or wrong....some people love one combination but not another, so even if GIA says something is great and AGS says not, then someone else may think it's vice versa. i've learned from hanging out here and looking at various combinations of diamonds in person that you really have to go with what your eye feels is beautiful, even if sometimes the numbers don't match.

but that said if you are buying virtually with only numbers and images to go off of, for me neither of those stones would be my first pick, i have more of a play it safe range and those numbers are totally out of it.

 

[strmrdr]

im going to redo them later with a thinner girdle.
The girdle I picked kicks the second one to ags1 if they are both the same.

 

[Houseparty]

Hi,
Thanks to anyone that has replied to this post. This was inteded as an academic / theoretical question, not "which one of these two stones should I buy". Sorry if I misled anyone. I still find it very interesting that these two premier institutions would see things so differently. I understand personal preference, but at some point I would think that the best in the industry would have more consensus on preferred cut ranges.

I look forward to your further comments.

David

 

[valeria101]

Date: 3/12/2006 3:22:48 PM
Author: Houseparty

I still find it very interesting that these two premier institutions would see things so differently.

I am quite sure you can find very reputable and very diverging opinions about these things.

Lab reports are mainly purchased by jewelers, not directly by the public. And are advertised to the trade as 'branding devices'. So, what good would that do if the papers agree? As much as I understand, it makes commercial sense to have them disagree a bit... around the corners

Not much enough to make technically unacceptable claims, not little enough so as to make the reports entirely equivalent.

There may be some more profound reason why there is disagreement, but ... not that I understand.


Sure enough, diamonds are diamonds and they blissfully ignore what paper comes with them.

There's enough info floating around to make your own rules, if you wanted to. (IMO)

 

[valeria101]

Btw. there has been allot of talk about these differences - and they are not just about those angles...

You must have seen THIS I suppose (thread just started by John Q, comparing GIA''s and AGS''s top cut ranges, by table size and angles).

GIA''s decision to add a measurement of the minor facets in the mix, and the two lab''s opposite take on brilliantring make some hundreds of posts since the beginning of the year (and launch of GIA''s new cut grades).

 

[Houseparty]

I do not believe that I have see that thread. I must not be searching very well. Any tips to help me find that thread.

Thanks

 

[mrssalvo]

if you click on the word "THIS" is val's post it will take you to the thread

 

[Houseparty]

Never mind, you sent me the link, I have seen it. Thanks