Why is this GIA Ex/Ex/Ex predicted to be UGLY by HCA?

[Megenoita]

I''m guessing that the crown angle/pavilion angle relationship is what does it, but what specifically can we assume from the stone''s details? HCA gives this diamond a 4.6 (G/G/G/VG):

GIA RBC
7.73 x 7.8 x 4.74 mm

1.76 G VS2

Ex Cut
Ex Polish
Ex Symmetry
No Fl

Comments: Additional clouds are not shown.

Additional Inscription: H&A

Table: 60
Depth: 61
Crown angle: 33.5
Pav. angle: 41.4

Crown height %: 13.5
Pav. D %: 44
Girdle Med-Slk, faceted

Lastly, do I need to be worried about the comment?

Thanks,
M

 

[jet2ks]

The pavillion angle is a little steep, especially with a 60% table. This is the main reason that the HCA is giving that score--it is not predicting ugly, it is just saying that the odds of it being a top performer are low. Personally, I would pass and keep looking.

 

[Megenoita]

Very interesting...it just makes me wonder why GIA would give this such a high cut score.

Thanks for the reply!

 

[Rockdiamond]

GIA is basing it's grade on physical inspection.
HCA, and others are using angles to attempt to predict what the stone may or may not look like. It would be impossible to guarantee what the stone looks like without looking at the actual diamond.
Plus, there's a matter of opinion.
What some people love, others do not- all within the GIA cut grade of EX

Have you seen the diamond?

 

[Megenoita]

I''m pretty sure GIA''s grading system is NOT based on physical inspection at all, but a mathematical formula. I stated in a PS thread awhile back that I thought GIA graded based on physical inspection and I was shown to be wrong by many posters.

I just saw the stone listed tonight, and I''ve not seen it in person yet.

Thanks,
M

 

[stone-cold11]

Unless you have IS/ASET image of the stone, pass.

 

[ChunkyCushionLover]

Date: 12/14/2009 6:36:21 PM
Author: Megenoita
I''m pretty sure GIA''s grading system is NOT based on physical inspection at all, but a mathematical formula. I stated in a PS thread awhile back that I thought GIA graded based on physical inspection and I was shown to be wrong by many posters.

I just saw the stone listed tonight, and I''ve not seen it in person yet.

Thanks,
M

GIA grades by numerical ranges that were determined by surveys of diamonds viewed in person by industry professionals.
The GIA range is wide enough to make many vendors happy and allow enough diamonds to receive the grade, even though some within this range can have considerable leakage under the table.

It would be in your interests to compare an ideal cut diamond that shows no leakage with this 60% table one and see which one you prefer.

 

[Regular Guy]

Date: 12/14/2009 6:29:25 PM
Author: Rockdiamond
GIA is basing it''s grade on physical inspection.
HCA, and others are using angles to attempt to predict what the stone may or may not look like. It would be impossible to guarantee what the stone looks like without looking at the actual diamond.
Plus, there''s a matter of opinion.
What some people love, others do not- all within the GIA cut grade of EX

Have you seen the diamond?

David, you''re not serious, are you?

I had to google GIA cut grade to find this. You should know this.

 

[Rockdiamond]

Sorry for the unclear statement:
GIA's cut grade is based , in part, on physical observations of thousands of stones. The information garnered was extrapolated to numerical data which is how the stone in question got it's grade.
Although the stone itself was not examined for cut the grade itself is based on physical observations.
CCL feels they used only tradespeople, I don;t know about that part.

 

[Dreamer_D]

I would keep looking. There are many diamonds out there that will have better proportions, why not keep looking?

 

[FB.]

Not all GIA Ex stones appeal to everyone. This is one of those stones that is a "love or hate" type.

This one has a deep pavilion and a slightly flat crown.
Not most people's idea of ideal, but this stone may still have reasonably complementary crown and pavilion angles and is likely to have greatly reduced prominence of the black arrows.
Some people don't like the black arrows on a Tolkowsky ideal cut, so they actively seek-out stones without the prominent black arrows, which lie around the 33.5' crown and 41.3' pavilion angles. They accept a moderate reduction in light performance as a trade-off to get rid of the black arrows.

Not a stone to be recommended to your average diamond buyer, but a stone that would particularly suit some people.

See my "return of the steep deep" thread from a couple of weeks ago, for more chatter about these "arrow-less" stones.

 

[FB.]

Date: 12/14/2009 6:59:39 PM
Author: Rockdiamond
Sorry for the unclear statement:
GIA's cut grade is based , in part, on physical observations of thousands of stones. The information garnered was extrapolated to numerical data which is how the stone in question got it's grade.
Although the stone itself was not examined for cut the grade itself is based on physical observations.
CCL feels they used only tradespeople, I don;t know about that part.

David

It is very likely that this stone does not suffer from the "arrows of death" often found in round diamonds - as we humorously called it a couple of weeks ago.

 

[Megenoita]

Date: 12/14/2009 6:59:39 PM
Author: Rockdiamond
Sorry for the unclear statement:

GIA''s cut grade is based , in part, on physical observations of thousands of stones. The information garnered was extrapolated to numerical data which is how the stone in question got it''s grade.

Although the stone itself was not examined for cut the grade itself is based on physical observations.

CCL feels they used only tradespeople, I don;t know about that part.

David, the statement was clear when you first said it:

GIA is basing it''s grade on physical inspection.
HCA, and others are using angles to attempt to predict what the stone may or may not look like. It would be impossible to guarantee what the stone looks like without looking at the actual diamond.

You were making the point that you thought GIA physically inspected the stone prior to their cut grading, and that is better than the HCA which is only a prediction based on actual observation testing. If we take your amended statement and fit it into your first statement, it refutes itself and makes no sense:

GIA is basing its grading on mathematical predictions based on actual observation testing. HCA, and others are using angles to attempt to predict what the stones may or may not look like (same exact method as GIA). It would be impossible to guarantee what the stone looks like without looking at the actual diamond (which GIA does not do for the cut grade).

You might argue that GIA''s observation testing was more thorough and done by trades people, but these were not part of your original argument. Your argument was that GIA is better than HCA and others because of actual physical inspection.

I admit that *seeing* the stone is ideal, but for long distance purchases, a combo of GIA/AGS cert, HCA, and ASET are what I have to go with.

 

[Megenoita]

Very cool info...I assume this would mean greater brilliance but less contrast? And perhaps less fire? Because the black arrows create the contrast and fire in the stone, yes?

 

[Rockdiamond]

Your initial post questioned how a GIA EX cut grade is downgraded by HCA.
GIA''s grade IS based on physical observation of thousands of diamonds.
I suppose we might be able to say the same about HCA when Garry designed it.
Does not change my intent of my original post that I do feel that GIA''s cut grade is far more useful, and relevant as compared to HCA.

If you want to trust HCA over GIA that is clearly your choice.
I don''t.


To my knowledge, GIA''s cut grade testing was NOT done solely on tradespeople, but we can check that part out.

 

[FB.]

Date: 12/14/2009 7:21:47 PM
Author: Megenoita
Very cool info...I assume this would mean greater brilliance but less contrast? And perhaps less fire? Because the black arrows create the contrast and fire in the stone, yes?

The angles border on not being complementary, so some light return is sacrificed, and with it, the other features of a diamond.
Contrast/scintillation suffers without the black arrows. But the lack of black arrows is precisely what some people seek.
The arrows will lack much of their fire, but other parts of the stone will still have fire. I seem to notice that the fire of 33/41 angle combinations seems to have fewer flashes, but that the flashes are larger in size and tend to last a bit longer than a Tolkowsky cut.
A 35.0/40.6 Tolkowsky-type is like being machine-gunned with sparks of fire. A 33.0/41.0 is more like being hit by a few bazooka shots of fire. 33.5/41.4 sacrifices a little more to get rid of the arrows.
Both the 35/40.6 and 33/41 are impressive - but different. A 34.7/40.8 Tolkowsky is probably the safest bet. To an untrained eye, a Tolk looks to have more sparkle because of the dozens of sparks.

 

[BobR]

Date: 12/14/2009 7:19:30 PM
Author: Megenoita

Date: 12/14/2009 6:59:39 PM
Author: Rockdiamond
Sorry for the unclear statement:

GIA''s cut grade is based , in part, on physical observations of thousands of stones. The information garnered was extrapolated to numerical data which is how the stone in question got it''s grade.

Although the stone itself was not examined for cut the grade itself is based on physical observations.

CCL feels they used only tradespeople, I don;t know about that part.

David, the statement was clear when you first said it:

GIA is basing it''s grade on physical inspection.
HCA, and others are using angles to attempt to predict what the stone may or may not look like. It would be impossible to guarantee what the stone looks like without looking at the actual diamond.

You were making the point that you thought GIA physically inspected the stone prior to their cut grading, and that is better than the HCA which is only a prediction based on actual observation testing. If we take your amended statement and fit it into your first statement, it refutes itself and makes no sense:

GIA is basing its grading on mathematical predictions based on actual observation testing. HCA, and others are using angles to attempt to predict what the stones may or may not look like (same exact method as GIA). It would be impossible to guarantee what the stone looks like without looking at the actual diamond (which GIA does not do for the cut grade).

You might argue that GIA''s observation testing was more thorough and done by trades people, but these were not part of your original argument. Your argument was that GIA is better than HCA and others because of actual physical inspection.

I admit that *seeing* the stone is ideal, but for long distance purchases, a combo of GIA/AGS cert, HCA, and ASET are what I have to go with.

Hi I''m no expert but my understanding of the GIA cut grade assignment is that it is in the large part predictive. i.e a tentative grade is assigned based upon correlation of the stones proportions to a mathematical extrapolation of those from its observation testing ( for which GIA publishes tables and/or free software to establish). However the stone is also subjected to physical examination for painting/digging beyond a specified tolerance which can result in downgrading of the cut for that specific stone. There may be other factors in the physical examination that can result in a grade adjustment but I have no detailed knowledge here, - perhaps one of the experts can clarify!! (I hope one of the experts willl correct me if I''ve got anything wrong).

 

[FB.]

Date: 12/14/2009 7:42:29 PM
Author: BobR



Hi I'm no expert but my understanding of the GIA cut grade assignment is that it is in the large part predictive. i.e a tentative grade is assigned based upon correlation of the stones proportions to a mathematical extrapolation of those from its observation testing ( for which GIA publishes tables and/or free software to establish). However the stone is also subjected to physical examination for painting/digging beyond a specified tolerance which can result in downgrading of the cut for that specific stone. There may be other factors in the physical examination that can result in a grade adjustment but I have no detailed knowledge here, - perhaps one of the experts can clarify!! (I hope one of the experts willl correct me if I've got anything wrong).

Bob,

This board does not generally approve of GIA-Excellent-cut "steep deep" stones - 35.5/41.2 and greater angle combinations.
But the plus point of 41.2 and deeper pavilions (depending on crown angle) is that the black arrows tend to disappear. Some people like that effect because they don't like eight black arrows staring them in the face.
Unfortunately, going too steep/deep produces the black ring around the edge of the table instead of the black arrows. But some people prefer the "ring of death" to having black arrows.

 

[BobR]

Date: 12/14/2009 7:19:30 PM
Author: Megenoita

Date: 12/14/2009 6:59:39 PM
Author: Rockdiamond
Sorry for the unclear statement:

GIA''s cut grade is based , in part, on physical observations of thousands of stones. The information garnered was extrapolated to numerical data which is how the stone in question got it''s grade.

Although the stone itself was not examined for cut the grade itself is based on physical observations.

CCL feels they used only tradespeople, I don;t know about that part.

David, the statement was clear when you first said it:

GIA is basing it''s grade on physical inspection.
HCA, and others are using angles to attempt to predict what the stone may or may not look like. It would be impossible to guarantee what the stone looks like without looking at the actual diamond.

You were making the point that you thought GIA physically inspected the stone prior to their cut grading, and that is better than the HCA which is only a prediction based on actual observation testing. If we take your amended statement and fit it into your first statement, it refutes itself and makes no sense:
GIA is basing its grading on mathematical predictions based on actual observation testing
. HCA, and others are using angles to attempt to predict what the stones may or may not look like (same exact method as GIA). It would be impossible to guarantee what the stone looks like without looking at the actual diamond (which GIA does not do for the cut grade).

You might argue that GIA''s observation testing was more thorough and done by trades people, but these were not part of your original argument. Your argument was that GIA is better than HCA and others because of actual physical inspection.

I admit that *seeing* the stone is ideal, but for long distance purchases, a combo of GIA/AGS cert, HCA, and ASET are what I have to go with.

FB
Thanks for your comments, and I''m awaiting our first set of tolkowsky h&a with baited breath ( I hope my wife likes the arrows) as her existing stones, whilst meeting GIA Ex /AGS Ideal proportions, do not exhibit the arrows.
However the point I was trying to make was purely in response to the highlighted comment that GIA grading is purely predictive as is HCA.
As I understand it this is not the case - physical inspection of the specific stone is done for painting/digging/girdle/polish/symmetry and maybe other factors??

 

[Megenoita]

Is the Cut Grade aspect of GIA''s grading PURELY predictive? Or is there a check for "painting/digging" as one person suggested?

What I KNOW is that GIA doesn''t look at the stone and see how brilliant it is and classify it based on visual observation.

 

[BobR]

The link below shows what GIA says about its physical inspection of a stone

http://www.gia.edu/diamondcut/06_estimating_a_cut_grade.html#considerations

One other point is that for the proportions in the original post and per tables from Octonus website the AGS Gold (2d predicted grade) is AGS (Ex) and AGS pgs (3d predicted performance grade) is AGS(0). So GIA and AGS substantially agree on this.