Consumer advisory: GIA Cut Grade Rounding Problems

[JohnQuixote]

To be concise, this thread is about:


1. Cut grade conflicts caused by the forced rounding in GIA's new system.

...The cut grade GIA assigns will vary (a) depending which direction the actual angles are rounded in, and (b) if necessary adjustments aren't made to overall depth - perhaps girdle thickness too - when this forced rounding occurs.
2. GIA appears to be downgrading diamonds with non-traditional brillianteering even when the approach is additive.

...This goes against prior assertions that girdle approaches would have to be 'deleterious' to receive a downgrade.


3. Perhaps more as we go.





[ The next several posts were discussed in the 2006 GIA Grading Report thread, page 3. These types of issues appear to be surfacing in public now, so I am reposting it again with a consumer heading ]



GIA Cut Grades (Facetware and online): Adjustments for rounding

The GIA grading system appears not to make necessary adjustments in depth, girdle (and perhaps other parameters) when the software default-rounds angles.

Some time ago Strmrdr pointed out a depth adjustment necessary due to FW rounding and I put these examples together for our staff. These were done with the old interface, but the results are the same with the new one.

Hopefully this will be useful info for anyone who will be using (or who's clients will be using) the software.

Example A: You may receive different grades depending on your rounding choice

Depth: 60.8
Table: 55
CA: 35
PA: 40.7
Star: 50
LH: 80
Girdle: Thin to Medium
Culet: N
Polish: Ex
Sym: Ex

In this example the diamond’s PA is 40.7. Your choice between 40.6 and 40.8 is the difference between EX or VG/worse. Facetware awards EX when you choose to enter 40.6 (likely because the CA is high at 35.0 and 40.8 would make the diamond too steep for its tastes). Thus, two different grading implications can be produced for any diamond with these measurements.

Consider also that any diamond with a 34.8 or 34.9 CA average will be forced to 35 in FW, so you will be faced with the same choice in FW for any of these combined with 40.7.

 

[JohnQuixote]

The next 2 examples are near the border of ideal-shallow, showing how Facetware gives a VG rather than an EX result - not due to PA/CA combination, but for failing to adjust depth when forced to round (credit to Strm for first pointing this out a while back).

Example B: Depth adjustment for Pavilion Angle rounding

Depth: 59.9
Table: 56
CA: 34.4
PA: 40.5
Star: 50
LH: 80
Girdle: Thin to Medium
Culet: N
Polish: Ex
Sym: Ex

The Given PA is 40.5. Facetware forces a choice between 40.4 and 40.6 PA. For this example, select 40.6 rather than 40.4. The numbers result in VG (‘Predicted Grade for Diamond 1’ below) but not due to PA/CA combination. The problem is the PA was raised from 40.5 to 40.6 but there was no adjustment to overall depth when you made the diamond slightly deeper. Adjusting depth from 59.9 to 60.0 results in a grade of EX (‘Predicted Grade for Diamond 2’).

 

[JohnQuixote]

Example C: Depth Adjustment for Crown Angle Rounding

Depth: 60.3
Table: 55
CA: 34.3
PA: 40.6
Star: 50
LH: 80
Girdle: Thin to Medium
Culet: N
Polish: Ex
Sym: Ex

The CA average is 34.3. Facetware forces it to 34.5. Again, VG results (‘Predicted Grade for Diamond 1’) but not due to CA/PA. Here also, the problem is raising the diamond’s CA a full .2 degrees to 34.5 but not adjusting overall depth. Adjusting the 60.3 up to a 60.4 (or 60.5) results in a grade of EX (‘Predicted Grade for Diamond 2’).

 

[JohnQuixote]

Graphic

 

[Lynn B]

Thanks for the new thread, John.

I said this before in the other thread, but that is just (IMHO) plain *STOOOOPID* of GIA to do that forced rounding! To me, it completely devalues their so-called cutgrade.

As a proud and certified HAIR-SPLITTER

who searches very long and very hard for juuuuust the perfect numbers, I do not appreciate that arbitrary rounding!

 

[JohnQuixote]

Example from rstillin:

Sarin: 60.2 56.8 40.7 35.0 Girdle Med-Med PG SVG

GIA: 60.2 57.0 40.8 (rounded) 35.0 Girdle reported at thin-med

First thoughts:

1. Perhaps rounding PA from 40.7 to 40.8 caused the software to think the diamond's girdle was thin enough to receive 'fair'? This would be in-line with the errors noted above.

2. Perhaps 'non-traditional' brillianteering (painting) caused the downgrade?

 

[JohnQuixote]

RStillin''s example in Facetware. FW awards a ''Very Good.''

Perhaps brillianteering is the issue then? If so, it''s not very ''brilliant'' I''m afraid.

 

[adamasgem]

Date: 1/29/2006 4:31:03 PM
Author: JohnQuixote
RStillin's example in Facetware. FW awards a 'Very Good.'

Perhaps brillianteering is the issue then? If so, it's not very 'brilliant' I'm afraid.

John: It should be called FARCEWARE(TM), as I've said before, not FacetWare(TM), especially if they can't truthfully and CORRECTLY categorize and CUT GRADE "painted" brillianteering of the crown girdle facets, for the exceptional stones they can be, whoever is cutting them, EightStar or WhiteFlash.

In fact, by KNOWINGLY, INTENTIONALLY, RECKLESSLY and INCORRECTLY grading them relative to "normal" brillianteering, thereby damaging the reputation of a cutter, after the fact of the original issuing of the report (note the original date), I wouldn't be too surprized if someone didn't sue GIA/GTL. They might have a VERY good case, But that's my non legal opinion.

I guess they are just too lazy to do it right...

 

[JohnQuixote]

(At the risk of causing Marty to make his font size even LARGER...)


Here is another example.

Proportions and finish are (what I think we would all) predict as a strong performer (HCA 1, Ex Ex Ex Ex).

Likely an AGS 0, if it had Ideal polish/sym.

(edited to add: continued after Marty's mini-rant just below)

 

[adamasgem]

On non "standard" brillianteering, GIA/GTL should be more forthcoming, instead of giving a false and misleading cut grade, since they know they have, they should just say, "we don''t know how to correctly grade these stones, send it to AGS for a cut grade and we will pay for it."

 

[JohnQuixote]

(continued)

... Likely an AGS0, if it had ideal polish/sym.


But... Step right up and pick your grade.


GIA could give it 3 different grades


EX: Rounding the 40.7 PA to a 40.6 (see below)
VG: Rounding the 40.7 PA to a 40.8 (see below)
G: Report Check (which rounded to a 40.8 and then presumably downgraded for non-traditional brillianteering - next post)

 

[JohnQuixote]

Report check.

Hold on for the ride folks.

 

[belle]

as it stands
i am leary of gia''s intentions

 

[valeria101]

Date: 1/29/2006 5:36:38 PM
Author: JohnQuixote

Hold on for the ride folks.

Blah.... And I was complaining (at times) about the HCA. It does allot better, doesn''t it ?

Wasn''t 8* using GIA? It sounds like allot of nerve to call those diamonds ''Fair'' crap

Looking forward to a WF ''Expert Selection'' populated by AGS and... maybe your own house grades? It would sound better than this mess.

 

[Garry H (Cut Nut)]

Before we throw 2 much mud - it would be good to have .gem files or Sarin srn''s to check that the girdles are not too thin at 1 spot.
But i expect the reason is the upper girdle facet painting

GIA has made it clear for a long time that they do not like it.

Or perhaps we should say the conventional trade elements that participated in the survey probably did not like anything that looked too different (or better) than their own goods.

 

[Mara]

I haven't really been following all of these threads but I did catch onto this today when I saw that other post....I personally find the rounding pretty freaky! I also checked out a few samples of what GIA is calling Excellent. aka there was a 58% tabled, 60.4% depth with something like 33.5 crown angle and 41.2 pav angle...personally I would not be all that interested in a stone like that even though GIA is terming it excellent..since I know from experience that my sweet spot has different numbers and a smaller table.

Well, just like the old AGS0 didn't guarantee a beautiful diamond from a range of numbers, seems that the new GIA cut grading is just as inaccurate.

 

[Garry H (Cut Nut)]

Mara and everyone who has not been following the technical threads.

1. Click on the file at the bottom of this post
2. go thru the opening instructions

What you will find is a comparison like the one Leonid and I did with AGS candidates on the HCA charts.

AGS have been very open.

GIA have announced that building this chart attached here is illegal. Marty Haske was given it by someone, I genuinely do not know who, but in the interest of education and understanding it will make things a lot more dlear for you.

Perhaps you can understand why I have been so concerned.
There are stones that HCA gives >5 that rate GIA excellent.

Yet we are seeing stones AGS would give AGS 0 get GIA Feir.
It is my worst fear for the confidence in our industry.

 

[Garry H (Cut Nut)]

Here is a model of that WF stone with its DiamCalc LR and contrast

 

[Regular Guy]

Back in the day, there was a very funny Saturday Night Live skit...no, no...it was probably Doonesbury...where then President Ronald Reagan was giving a press conference, and the reporters around the president, to his dismay, were talking about why whatever the president was saying wasn''t hurting him, because of the "teflon" nature of his character.

Why don''t we be what I think is realistic, and ascribe to GIA neither idiocy, nor incompetency, but instead, try to impute the ostensible rationale for why they would implement this bit of impure science as their MO. I think they have somewhere said as much, we can see the outline of the problem solving for this practice, and we have seen here the consequences of the practice. Although the idea is out there, I think it does need to be fleshed out a bit. Frankly, I have to think that their original idea, logically, could have been consistent with speculation on this board 1/2 year ago...that they were "lifting up the top" without dragging up the bottom, leaving a very large set of options that could have been assigned excellent, and at some point, changed the protocols, such that the results become both more arbitrary, and less meaningful, than if they simply held out a wide excellent category...such that now we don''t know if good are bads or if those marked bads are really goods.

GIA wants to be protective and functionally helpful to the appraisers it provides instruction to, it acknowledges that it tells them they can do their job, only measuring using the diamond proportion analyzer that they train them to use, and these instruments measure very poorly, with respect to measurement error. (Actually, I had been led to believe they provide data so imperfect that this argument may not believable in any respect, but let''s try). So, the crux of what we must think is GIAs idea with intentional rounding is perhaps this...they would want to give the benefit of the doubt to a provisionally nicely proportioned diamond measured to its detriment with the diamond proportion analyzer, so that, were its inherent measurement error accounted for, it could still be regarded as the well cut diamond this theoretical diamond could be. Anyway, I had thought all along this was the nature of the provisional argument.

If this is so, something must have gone wrong. They have not just opened up the lid to include a wider net, preventing potentially nice diamonds from being excluded because of actual measurement error....but they have somehow, presuming the original idea is recorded correctly here, also then sought to re-truncate those options that are well cut, imputing assumptions about them that the rounding they created causes the opposite effect they intended, and has been effectively documented here, as frequently as not making well cut diamonds into poorly cut ones.

There are huge black holes in this thought process. Figuring out how that core argument was going to work by way of adding rounding is one piece of the puzzle. Another is figuring out what if anything is to be understood from the consequences of this practice...i.e., is there any sense that the scores resulting from these practices are actually strategically arrived at by GIA, and if so, what exactly is meant by these results. In the alternative...with Pricescope on the one hand, and their own brillianteering engineers in place on the other, since these confounds are being made manifest, what can we judge to be the outcome of the continued proliferation of reporting of diamonds with information associated with it that does not describe the characteristics of the stone.

Whereas JohnQ had only recently found it helpful to lift up GIA''s pitard, and say they may not be very good, but at least they''re making things better, it seems their defender has found it necessary to take a fresh look, and question the changes that were assumed to be positive. Seems like it could be useful to walk through just what it seems to be that has happened here altogether...specifically with respect to both the details of both what protocols have been implemented, parallel to what must have been intended with these changes.

 

[Garry H (Cut Nut)]

Date: 1/29/2006 9:31:44 PM
Author: Regular Guy
Seems like it could be useful to walk through just what it seems to be that has happened here altogether...specifically with respect to both the details of both what protocols have been implemented, parallel to what must have been intended with these changes.

Ira it seems they used a light box and light colored tray that improves the appearance of diamonds with steep deep proportions.
They also found girdle variations caused by painting and digging a bit complex top understand, so they dont want anyone to do it.

What is more interesting though is how they got 38,000,000 proportion combinations when they round so brutally. (any mathematicians like to estimate what proportion range they must have used? - maybe 5- 75 degree crown angles etc etc )

 

[Regular Guy]

Date: 1/29/2006 9:43:33 PM
Author: Garry H (Cut Nut)

Date: 1/29/2006 9:31:44 PM
Author: Regular Guy
Seems like it could be useful to walk through just what it seems to be that has happened here altogether...specifically with respect to both the details of both what protocols have been implemented, parallel to what must have been intended with these changes.

Ira it seems they used a light box and light colored tray that improves the appearance of diamonds with steep deep proportions.
They also found girdle variations caused by painting and digging a bit complex top understand, so they dont want anyone to do it.

What is more interesting though is how they got 38,000,000 proportion combinations when they round so brutally. (any mathematicians like to estimate what proportion range they must have used? - maybe 5- 75 degree crown angles etc etc )

I would agree that there are two pieces to look at...their conclusions about what looks good...your first part above....and then what should be (but are not) incidental issues of how measurements are made to arrive at the conclusions. But, the fact of rounding is the subject of this thread. I thought it might be helpful to get at what underlies what has become the tail wagging the dog in this analysis, where what should have been the incidental matter of data recording has become the more pronounced concern...both in this discussion, and perhaps to anyone trying to find any kind of value in a contemporary document from GIA.

 

[RockDoc]

Here''s yet another BLACK HOLE ............


Among the experts, variances need to be made based on the diameter of the stone.

Even AGS''s charts are limited to 6 mm stones.

Could it be that the wider acceptable proportions on their system are made without quantification that only certain propoertional comibination are for particular diameter measurements???

Do those change at 1/2 mm increments ? Or maybe full 1 mm proportion variances are more proper?

I am of the opinion, that as we keep splitting the hair, this has to be on the menu of potential change/adjustment.

Rockdoc

 

[Garry H (Cut Nut)]

Ira:

Date: 1/29/2006 4:11:53 PM
Author:JohnQuixote

To be concise, this thread is about:


1. Cut grade conflicts caused by the forced rounding in GIA''s new system.

...The cut grade GIA assigns will vary (a) depending which direction the actual angles are rounded in, and (b) if necessary adjustments aren''t made to overall depth - perhaps girdle thickness too - when this forced rounding occurs.
2. GIA appears to be downgrading diamonds with non-traditional brillianteering even when the approach is additive.

...This goes against prior assertions that girdle approaches would have to be ''deleterious'' to receive a downgrade.

3. Perhaps more as we go.

Roc: "Even AGS''s charts are limited to 6 mm stones."
Not true - round charts are available in 4mm, 6mm, 8mm, 10mm, and 12mm.
Only princess comes in one size fits all - which i believe is 6mm.

 

[Garysax]

Looks like you might as well treat the GIA cut value with the same skepticism you should treat, say and EGL cut value. The fact that it is largely caused by rounding issues IS very odd, though.

I do share your concerns about the average consumer not looking at a lot of great diamonds because of this, though. Which is terrible because this was supposed to be a solution to get the average consumer more involved and informed with cut! And if I had an in house "expert selection" type diamond range I''d be pretty upset about it too, if my stones were recieving "fair" ratings for no good reason.

 

[old timer]

This is such an interesting topic, I feel compelled to stick my nose in. I am a retail jewlery veteran of 33 years , I know my business, but am absolutely not as qualified as those of you that are GG''s. None the less, I am in wholehearted agreement with your displeasure of GIA''s rounding. I remember when I first heard they were going to grade cut. I wondered how in the world they could possibly pull it off accurately. As one of you so aptly put it, this can be detrimental to the cutter in the long run. By rounding and stating these specs in a written report, they are devaluing what is most likely a beautiful gem. We all know that today''s consumer is more well read than those of "yesteryear". They put their faith in the lab analysis instead of viewing the diamond at the same time as the cert. I firmly believe that this is going to have a negative impact on the retail industry and promote the selling of "paper" as opposed to the gem in all of it''s glory. Sometimes we forget that this is mostly romance, not a science project! We do not want to forget that customer that is on a limited budget and is perfectly content with a 2M.(or 3M, for that matter) This type of information will make this consumer feel they are not getting quality goods. I in no way want to make my customer feel that they cannot afford a beautiful diamond or cause them to believe that these cut grades are the final word. Well, guess it''s time to get off my soapbox! Thank you all for listening.


Vel

 

[RockDoc]

Roc: "Even AGS''s charts are limited to 6 mm stones."
Not true - round charts are available in 4mm, 6mm, 8mm, 10mm, and 12mm.
Only princess comes in one size fits all - which i believe is 6mm.
The Holloway Cut Adviser & Ideal-Scope Cut Crusader!
www.ideal-scope.com
www.preciousmetals.com.au


With my ASET desktop and hand held shipment, I only received 6mm charts.... and just two of them. NO chart for princess cuts.

This is the first I''ve heard of this. If they exist and are a part of the "ASET" system, guess they should have been included..

Rockdoc

 

[Garry H (Cut Nut)]

Date: 1/30/2006 1:34:35 AM
Author: RockDoc
Roc: ''Even AGS''s charts are limited to 6 mm stones.''
Not true - round charts are available in 4mm, 6mm, 8mm, 10mm, and 12mm.
Only princess comes in one size fits all - which i believe is 6mm.
The Holloway Cut Adviser & Ideal-Scope Cut Crusader!
www.ideal-scope.com
www.preciousmetals.com.au


With my ASET desktop and hand held shipment, I only received 6mm charts.... and just two of them. NO chart for princess cuts.

This is the first I''ve heard of this. If they exist and are a part of the ''ASET'' system, guess they should have been included..

Rockdoc

Aha - we are talking at crossed purposes Bill.
I am referring to the charts that manufacturers use with ranges of crown and pavilion angles on seperate table sized charts.
You mean charts on ASET images like this ideal-scope one here
http://www.diamond-cut.com.au/06_firescope.htm

The size is not such a big issue for ASET.

 

[RockDoc]

Date: 1/30/2006 1:56:27 AM
Author: Garry H (Cut Nut)

Date: 1/30/2006 1:34:35 AM
Author: RockDoc
Roc: ''Even AGS''s charts are limited to 6 mm stones.''
Not true - round charts are available in 4mm, 6mm, 8mm, 10mm, and 12mm.
Only princess comes in one size fits all - which i believe is 6mm.
The Holloway Cut Adviser & Ideal-Scope Cut Crusader!
www.ideal-scope.com
www.preciousmetals.com.au


With my ASET desktop and hand held shipment, I only received 6mm charts.... and just two of them. NO chart for princess cuts.

This is the first I''ve heard of this. If they exist and are a part of the ''ASET'' system, guess they should have been included..

Rockdoc

Aha - we are talking at crossed purposes Bill.
I am referring to the charts that manufacturers use with ranges of crown and pavilion angles on seperate table sized charts.
You mean charts on ASET images like this ideal-scope one here
http://www.diamond-cut.com.au/06_firescope.htm

The size is not such a big issue for ASET.

Hi Garry

Yes sort of. They are the wall charts that they provide.

Hopefully waiting for the the AGS software to be released hopefully at the AGS conclave. Are you going to that, in April in Orlando ?

Rockdoc

 

[Garry H (Cut Nut)]

Date: 1/30/2006 3:14:21 AM
Author: RockDoc

Hi Garry

Yes sort of. They are the wall charts that they provide. Not as good as the ones in car panel beaters offices.

Hopefully waiting for the the AGS software to be released hopefully at the AGS conclave. Are you going to that, in April in Orlando ? No plans at present - just India next month and Vegas and Italy in June

Rockdoc

 

[Garry H (Cut Nut)]

Here is a combined chart Rocdoc - it has the GIA AGS for 57% table size and some ideal-scope images to highlight some of the differences.

GIA in its G&G article in Fall 2005 referred to the ideal-scope as a gadget for assessing symmetry. I could not believe that after all my efforts from working on light return got lumped in with Hearts and Arrows.

I quote from page 202 http://www.gia.edu/pdfs/cut_fall2004.pdf :-

Current claims about the superiority of
certain round brilliant diamond cuts focus mostly
on three approaches:
• The use of specific sets of proportions (e.g., those
for the AGS 0, the AGA 1A, “Class 1” cuts [as
previously taught by GIA Education], the HRD
“Very Good” grades, “Ideal” cuts, and
“Tolkowsky” cuts)
• The use of viewing devices to see specific patterns
or pattern elements in diamonds (e.g.,
FireScope, Symmetriscope, IdealScope, and various
“Hearts-and-Arrows”–style viewers)
• The use of proprietary devices, such as the
GemEx BrillianceScope and ISEE2, which measure
one or more of the following aspects of diamond
appearance: brilliance, fire, scintillation,
and/or symmetry

And later on page 224 :-
Optical Symmetry. One aspect of pattern-related
scintillation that has gained more attention in
recent years is often called “optical symmetry” (see,
e.g., Cowing, 2002; Holloway, 2004). Many people
in the trade use this term for “branded” diamonds
that show near-perfect eight-fold symmetry by displaying
eight “arrows” in the face-up position (and
typically eight “hearts” table-down) when observed
with specially designed viewers. To investigate the
possible benefits of optical symmetry, we included
several such diamonds in our observation testing.
We found that although many (but not all) diamonds
with distinct optical symmetry were rated
highly by our observers, other diamonds (with very
different proportions and, in many cases, no discernible
optical symmetry) were ranked just as high.
Therefore, both types of diamonds can receive high
grades in our system.