AGS Ideal Cut vs. AGS 0 Ideal cut?

[AndyDiamond]

I found a potential stone, that was GIA Triple Excellent. I wanted to ensure it has great light performance, so paid jeweler to ship it to AGS. Results came back in, and AGS gives 2 options on report. They can show AGS Ideal Cut on the Diamond Quality Report which doesn't show a Cut grade score. Or the other report option is the Diamond Quality Document which shows deductions for contrast and dispersion and just gets Cut score of 1, and Excellent rating instead of Ideal.

Just wanted the forum's input on the discrepancy.

 

[flyingpig]

You are absolutely confused with different terms that AGS uses, especially between Light Performance and Cut Grade.
The cut grade in the "Report" is proportion-based, just like GIA's system. Therefore, this report does not include Light Performance.
The cut grade in the "Document" is, however, based on 3D ray tracing, which measures light performance in dispersion, light leakage, brightness, and contrast.

You mentioned the stone is GIA graded and has potential. AGS porportion based grading agrees with GIA's cut score and your assessment. However, under 3D ray tracing, the stone lacks in dispersion and contrast, therefore it got 1 in light performance and therefore 1 in cut grade in the "Document".

Different methods, different cut grades.

 

[AndyDiamond]

To clarify, this is for a round brilliant. The proportions are 55.2% table and 62.1% depth with 34.4 degrees crown angle and 40.6 degrees pavilion angle. AGS shows for light performance, 0 deductions for Brightness and Leakage. .7758 deduction for Contrast and .5420 deductions in Dispersion. Do you think it's still a stone to consider or should I pass? Jeweler put this stone next to another AGS 000 stone, and I really can't tell the difference visually.

 

[flyingpig]

While it is not unusual to see some minor deductions for a well cut diamond with ideal proportions, I am a bit surprised to see enough deduction to lower the overall light performance to 1 for a stone with such proportions.

I suspect the girdle is potentially painted or dug-out. Need at least the actual photo to confirm. The IS/ASET image would be better.

 

[AndyDiamond]

Jeweler believes it's because of deviating crown angles. See attached crown angle measurements from Sarin machine. Also attached is believe some scope image from Sarin machine, not sure if it's IS or ASET. Also picture of the stone. Any insight would be appreciated.

While it is not unusual to see some minor deductions for a well cut diamond with ideal proportions, I am a bit surprised to see enough deduction to lower the overall light performance to 1 for a stone with such proportions.

I suspect the girdle is potentially painted or dug-out. Need at least the actual photo to confirm. The IS/ASET image would be better.

 

[AndyDiamond]

Correction, the attached Sarin report showing differing crown angles was just an example, not the diamond in question.

 

[AndyDiamond]

Attached is the correct Sarin image of the deviating crown angles, a few a bit shallow.

 

[flyingpig]

I think it is the combination of slightly thin arrows and a bit of painting that cause the deductions in contrast and dispersion.

Still, I am surprised.

It appears to be an execellent stone regardless.

 

[AndyDiamond]

What causes the thin arrows? Where is the painting at? Is it because of the one crown angle that is just 33.9 degrees?

Thanks

I think it is the combination of slightly thin arrows and a bit of painting that cause the deductions in contrast and dispersion.

Still, I am surprised.

It appears to be an execellent stone regardless.

 

[bmfang]

What causes the thin arrows? Where is the painting at? Is it because of the one crown angle that is just 33.9 degrees?

Thanks

My guess re skinny arrows is that the stone has lower halves/girdle percentage closer to 80%.

 

[Karl_K]

Attached is the correct Sarin image of the deviating crown angles, a few a bit shallow.

post the pavilion part of the report please.

 

[Karl_K]

My guess re skinny arrows is that the stone has lower halves/girdle percentage closer to 80%.

80% actual would not be a down grade.
My guess is the pavilion angles will tell the story.

 

[bmfang]

With GIA 40.6 pavilion, I’m guessing 5 PA’s closer to 40.5 with the balance being closer to 40.7

 

[Karl_K]

With GIA 40.6 pavilion, I’m guessing 5 PA’s closer to 40.5 with the balance being closer to 40.7

One at 40.45 would be enough to trigger some penalties.

 

[AndyDiamond]

I don't have the pavilion angle report. Attached is the GIA report and the tentative AGS reports. Lower Girdle halves length shows 80% on GIA report, and looks like 79% on AGS.

 

[Texas Leaguer]

Andy,
What you're seeing is the fact that the AGS Ideal light performance based grade is much stricter than the top grade in GIA. Your stone comes very close to AGS Ideal but doesn't quite make it because the ray tracer detected some deficits. GIA does not ray trace the diamond, it uses rounded and averaged measurements and compares it to a table that is somewhat broad to determine the grade.

As Karl mentioned the deficits could be related to pavilion measurements - pavilion angles or lower half lengths or a combination of both. In the ray tracer it is about how everything works together, including possibly some painting and/or digging as flyingpig mentioned.

What to do with that information depends on your goals.

 

[AndyDiamond]

Here's the image with all the angles. Does that explain the reason why? Jeweler is saying that even though this stone does not technically qualify as AGS 0 is actually closer to true Hearts & Arrows Cut, and better than many stones that qualify as AGS 0 but have much more shallow crown angles and further away from ideal cut proportions. Your thoughts?

 

[kmoro]

Here's the image with all the angles. Does that explain the reason why? Jeweler is saying that even though this stone does not technically qualify as AGS 0 is actually closer to true Hearts & Arrows Cut, and better than many stones that qualify as AGS 0 but have much more shallow crown angles and further away from ideal cut proportions. Your thoughts?

Yes, there is one PA of 40.4 .... as Karl K said:

One at 40.45 would be enough to trigger some penalties.

 

[AndyDiamond]

Hi,

Anyone else can chime in with input if this stone is still a winner despite not AGS 0? Is it true that some AGS 0 stones that are not within traditional H&A proportions actually will be worst performance in real life? For example, take a look at attached sample of AGS 0 stone, but looking at the ASET image is no where close to H&A. So although it's an AGS 0, would you consider it worst performing than the stone in question that is close to H&A but just graded as AGS 1 cut?

Thanks

 

[bmfang]

Going by that computer generated ASET, I wouldn’t go for that particular AGS000 stone. You can get outliers like this even in AGS Ideal, but the range of table, depth and proportion combos is not quite as large as what it is to get GIA XXX.

 

[kmoro]

Hi,

Anyone else can chime in with input if this stone is still a winner despite not AGS 0? Is it true that some AGS 0 stones that are not within traditional H&A proportions actually will be worst performance in real life? For example, take a look at attached sample of AGS 0 stone, but looking at the ASET image is no where close to H&A. So although it's an AGS 0, would you consider it worst performing than the stone in question that is close to H&A but just graded as AGS 1 cut?

Thanks

Actually, I still see the H&A pattern ... it’s the way it reflects light that looks different ... I think.

 

[Rhino]

What it may also be due to is something you're not seeing on either the AGS Report or the Sarin actually.

AGS's ray tracing also looks at

• Both 30 and 40 degree obstruction. On the AGS Report as well as Sarin you're only seeing 30 as indicated by the blue.
• Tilt performance. The ray tracer does not only look at the static ASET or light performance that we are seeing via Sarin or the AGS but actually rocks and tilts the diamond when it it making its determination for light performance, affecting overall cut grade.

These may in fact be the issues causing the "1".

 

[Texas Leaguer]

Hi,

Anyone else can chime in with input if this stone is still a winner despite not AGS 0? Is it true that some AGS 0 stones that are not within traditional H&A proportions actually will be worst performance in real life? For example, take a look at attached sample of AGS 0 stone, but looking at the ASET image is no where close to H&A. So although it's an AGS 0, would you consider it worst performing than the stone in question that is close to H&A but just graded as AGS 1 cut?

Thanks

@AndyDiamond, You pose a very interesting question.
I would say the AGS1 might actually have better overall light performance than this very borderline AGS0. The 1.701 is about as steep/deep as you will find in AGS0, and you can see a lot of table leakage in the ASET on the AGS report.

However, I don't believe we have seen an ASET of the AGS1 as the first one posted was not the correct one. Maybe you could clarify and if available post an ASET of the AGS1. It would be interesting to compare.

As far as facet precision goes, H&A is not directly factored into AGS light performance grading (or GIA of course). But if facet precision is too wonky it will likely result in deductions in the AGS ray tracer. It is common to see Ideal cuts that while not cut with super high levels of precision, have the right amount and distribution of brightness, contrast and fire to achieve AGS0. This is the place where Ideals and Super Ideals begin to separate.

 

[AndyDiamond]

Attached is the actual ASET again.

 

[Karl_K]

I like the first one better of the 2 its an honest ags1, slight issue but should be nice.
The second one is what a call an accidental ags0, just by chance on that scan everything aligned to get the grade.
Would it get the same grade on another scan on the same machine? It is highly possible it would not. It might get a 1 or a 2 or even 3.
A real aset would be interesting because I have seen real ASET images of the accidental ags0 that were a long way off from the generated images.
That is a strength and a weakness of the agsl system based on scans.
It can find odd combinations that score well but they could also be false positives due to scanner accuracy.

 

[Karl_K]

What it may also be due to is something you're not seeing on either the AGS Report or the Sarin actually.

AGS's ray tracing also looks at

• Both 30 and 40 degree obstruction. On the AGS Report as well as Sarin you're only seeing 30 as indicated by the blue.
• Tilt performance. The ray tracer does not only look at the static ASET or light performance that we are seeing via Sarin or the AGS but actually rocks and tilts the diamond when it it making its determination for light performance, affecting overall cut grade.

These may in fact be the issues causing the "1".

My guess is that it paddled to much over the arrow head at 40 triggering the penalty at the low main.
In the real world to some degree that area may be darker at greater distances than the rest of the stone because it is still obstructing.
40 is joke but it does help find these somewhat, but it does not find them for the same reason you would see on the hand.
Put it in an earring or a pendant and the issue goes away because of the longer viewing distances.

 

[Texas Leaguer]

I like the first one better of the 2 its an honest ags1, slight issue but should be nice.
The second one is what a call an accidental ags0, just by chance on that scan everything aligned to get the grade.
Would it get the same grade on another scan on the same machine? It is highly possible it would not. It might get a 1 or a 2 or even 3.
A real aset would be interesting because I have seen real ASET images of the accidental ags0 that were a long way off from the generated images.
That is a strength and a weakness of the agsl system based on scans.
It can find odd combinations that score well but they could also be false positives due to scanner accuracy.

I suspect that @flyingpig 's speculation about painting and digging might be at play. Usually some crown only painting is tolerated in the AGS system, but painting or digging on pavilion not as much. The CG ASET might suggest painting. If so, it could have combined with the issue on the mains to reduce contrast and dispersion just enough. I agree that seeing a real ASET or IS photo would be more diagnostic. Also, this Sarin is most likely taken on a machine outside the lab so is not exactly what the lab ran through the ray tracer.
Overall, on the basis of the ASETs available the AGS 1 looks really good and I would say it is likely to be a better performer in real life than the AGS0.
Like I said, this is an interesting case!

 

[Karl_K]

I suspect that @flyingpig 's speculation about painting and digging might be at play. Usually some crown only painting is tolerated in the AGS system, but painting or digging on pavilion not as much. The CG ASET might suggest painting. If so, it could have combined with the issue on the mains to reduce contrast and dispersion just enough. I agree that seeing a real ASET or IS photo would be more diagnostic. Also, this Sarin is most likely taken on a machine outside the lab so is not exactly what the lab ran through the ray tracer.
Overall, on the basis of the ASETs available the AGS 1 looks really good and I would say it is likely to be a better performer in real life than the AGS0.
Like I said, this is an interesting case!

Based on the scan(i know its not totally accurate for this but its what the labs uses for CG image) there shouldn't be enough painting/digging to kick it down.
Good point on the scan the grade being based on not being the one we are looking at.

 

[flyingpig]

Something I have noticed over many years is that AGS 3D ray tracing is relatively strict on contrast grading, but lenient on leakage grading. I think this is the reason why we often see high crown and high pavilion combos, which have leakage under the table, granted AGS 0. I don't think the 1.701 I SI 35.6/41 is an accidental AGS 0; this is intended. The market is full of steep and deep GIA EX diamonds. I even say AGS does not want to lose too many customers by punishing deep cuts.

AGS can still be strict with shallow cuts that have contrast issues, because GIA is also strict with pavilion angles less than 40.5.

 

[Texas Leaguer]

Something I have noticed over many years is that AGS 3D ray tracing is relatively strict on contrast grading, but lenient on leakage grading. I think this is the reason why we often see high crown and high pavilion combos, which have leakage under the table, granted AGS 0. I don't think the 1.701 I SI 35.6/41 is an accidental AGS 0; this is intended. The market is full of steep and deep GIA EX diamonds. I even say AGS does not want to lose too many customers by punishing deep cuts.

AGS can still be strict with shallow cuts that have contrast issues, because GIA is also strict with pavilion angles less than 40.5.

But it is far more complicated for cutters to cut to the margins of AGS0 and try to 'game the system' because the ray tracer will pick up any faults in the 3D model and penalize them. While you see tons of steep deeps in GIA EX, stones like the 1.701 AGS 0 are rare. I would agree with @Karl_K 's characterization that this is a bit of an 'accidental' or lucky Ideal.