Can Ideal Cut Diamonds be Leakers?

[D_]

So my understanding is we cannot buy diamonds online that only look good on paper, we need to look at light performance images to get a sense of how a diamond will perform if we are not able to look at it with our own eyes.

In cases when there are light leakages - it's usually somewhat easy to explain if even one the stones' specs fall outside the ideal parameters, "oh the stone is cut a bit deep" or "table too large", "pavilion too steep" etc2

If the diamonds look really good on paper though, even fall within the ideal H&A specs, scores <2 w/ HCA, and we're talking about when the stats complement one another, e.g. crown/pavilion combo of 35/40.6 on a 56 table, not 34/40.6 on a 56 table (even though technically, 34/40.6/56 are still withing the ideal ranges), what are some possible reasons for the IS & ASET images to show light leakages?

 

[pfunk]

I started a thread asking the same thing a while back. I asked for people to post examples with IS and ASET images and no one was able to show many. Yes, there were a couple examples but they were when the pavilion was getting up around 41 and the crown at 35 or higher. If you stick to complementing angles you're very unlikely to have much leakage, IMO. Having said that, I have seen some examples when trying to help others find a stone, even when the numbers were complementary. The leakage was minimal in those cases, and I'm not sure whether the eye would even be able to discern that.

 

[Rhino]

So my understanding is we cannot buy diamonds online that only look good on paper, we need to look at light performance images to get a sense of how a diamond will perform if we are not able to look at it with our own eyes.

In cases when there are light leakages - it's usually somewhat easy to explain if even one the stones' specs fall outside the ideal parameters, "oh the stone is cut a bit deep" or "table too large", "pavilion too steep" etc2

If the diamonds look really good on paper though, even fall within the ideal H&A specs, scores <2 w/ HCA, and we're talking about when the stats complement one another, e.g. crown/pavilion combo of 35/40.6 on a 56 table, not 34/40.6 on a 56 table (even though technically, 34/40.6/56 are still withing the ideal ranges), what are some possible reasons for the IS & ASET images to show light leakages?

Good question D.

We've found 2 instances when apparently great average angles produce adverse optics.

1. When the variances or deviations between the minimum and maximum angles vary too much. Ie. when you see 34.5 on a report (GIA or AGS) you're seeing the average of 8 crown mains. If the min/max varies too much it can impact the light performance score.
2. And/or coupled with varying azimuth angles. The average angles we see reported are facets cut in the north/south orientation. Since diamond is a 3 dimensional object, facets are also cut in the east/west orientation as well. If those facets ALSO vary and are not cut to the same precision it can also impact the light performance and appearance of the diamond.

I started a thread asking the same thing a while back. I asked for people to post examples with IS and ASET images and no one was able to show many. Yes, there were a couple examples but they were when the pavilion was getting up around 41 and the crown at 35 or higher. If you stick to complementing angles you're very unlikely to have much leakage, IMO. Having said that, I have seen some examples when trying to help others find a stone, even when the numbers were complementary. The leakage was minimal in those cases, and I'm not sure whether the eye would even be able to discern that.

I've shot video on this very subject showing ASET/IdealScope/AGS PGS/Sarin etc. 34.5/40.8 with AGS 2 light performance. On hand I don't have anything like this but below is a computer generated ASET of an AGS Ideal that we would consider a "loose" one.



Kind regards,
Rhino

 

[D_]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

eta: sorry, posted this question before reading pfunk's thread, can't delete. Pardon me if there are questions that has been addressed there. Reading it now.

 

[pfunk]

Rhino,

Do you have the measurements or sarin data on that AGS ideal ASET that you posted by any chance?

 

[D_]

Ah, got to that part.
The AGS 2 is an GIA X.
I think I remember reading that article too - something about ring of death, but can't find it

Pfunk, Karl brought up a good point on your thread too re painting & digging, which would be difficult to discern by just looking at the numbers. Would need ASET image.

 

[solgen]

Here's a one with a HCA of 1.3. GIA 3EX and AGS Ideal going by their 2008 proportion cut chart.


DEPTH - 62.2%
TABLE - 55.0%
CROWN ANGLE - 34.5°
PAVILION ANGLE - 40.8°

ASET-




GIA number 2186581395

 

[Texas Leaguer]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

Yes, this is the safe approach and is what is generally recommended here for evaluating GIA diamonds. Most stones are cut to the margins of GIA Ex parameters for weight retention purposes. And because the GIA grading system is based upon matching the averaged rounded numbers on the cert to predefined tables, and because facet precision is not accounted for in the system, cutters have quite a bit of lattitude for achieving the GIA EX grade. An ASET image informs you of leakage and other issues, and to an extent facet precision and painting and digging.

 

[Garry H (Cut Nut)]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

Yes, this is the safe approach and is what is generally recommended here for evaluating GIA diamonds. Most stones are cut to the margins of GIA Ex parameters for weight retention purposes. And because the GIA grading system is based upon matching the averaged rounded numbers on the cert to predefined tables, and because facet precision is not accounted for in the system, cutters have quite a bit of lattitude for achieving the GIA EX grade. An ASET image informs you of leakage and other issues, and to an extent facet precision and painting and digging.

Bryan GIA - GTL largely use Helium scannersfor rounds with software boundaries developed over time for rounds these days. There are facet precision factors of both azimuth and angle variations. There is an example that you can open from this page:
http://www.octonus.com/oct/products/helium/polish/

I believe visual microscopic evaluation and facet meet points are not as heavily weighted as they once were.

 

[D_]

Gary, what do you refer what's observed on the 3rd and 4th pictures 1/3 down the page?
(where the upper girdle line doesn't align with the pavilion facet line plus there's a ..."clipped portion"?)
And how does it affect performance of the diamond?

 

[D_]

*Garry

-apologies for typo-

 

[Garry H (Cut Nut)]

Gary, what do you refer what's observed on the 3rd and 4th pictures 1/3 down the page?
(where the upper girdle line doesn't align with the pavilion facet line plus there's a ..."clipped portion"?)
And how does it affect performance of the diamond?

Hi D, will try to attach a word doc report - not sure it will work - lets see - no, so I will do a screen shot of the main offenders.
these are very detailed reports - I made the VG factors red. This is not the one GIA uses - because this stone is both GIA XXX (and AGS PGS 0, but i suspect would not qualify for AGS ideal symmetry).
So in answer to your question - there are many things going on and it is possible to identify that this or that is the main offender - but really it is often a complex interaction between a host of factors and facet interplay.

 

[Texas Leaguer]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

Yes, this is the safe approach and is what is generally recommended here for evaluating GIA diamonds. Most stones are cut to the margins of GIA Ex parameters for weight retention purposes. And because the GIA grading system is based upon matching the averaged rounded numbers on the cert to predefined tables, and because facet precision is not accounted for in the system, cutters have quite a bit of lattitude for achieving the GIA EX grade. An ASET image informs you of leakage and other issues, and to an extent facet precision and painting and digging.

Bryan GIA - GTL largely use Helium scanners for rounds with software boundaries developed over time for rounds these days. There are facet precision factors of both azimuth and angle variations. There is an example that you can open from this page:
http://www.octonus.com/oct/products/helium/polish/

I believe visual microscopic evaluation and facet meet points are not as heavily weighted as they once were.

Garry,
You bring up an interesting point. It would be assumed that the GIA would use the most advanced and accurate scanning technology available as part of their take-in and evaluation process. It is known that they will demote an otherwise EX cut to VG if they detect significant painting or digging out. That determination is most likely based largely on the scan, and is reported specifically on the report under comments. So, in this aspect facet precision is taken into account (although there is some disagreement with the overly broad assessment of this penalty).

But the question your post raises is how is the other precision related data used or reflected in a GIA report. That is, if there are deviations in the helium scan that exceed the tolerances imbedded in the helium software, does that affect the GIA grading? And if so, how would a deduction for say deviation in pavilion angles be reflected in a GIA report?

 

[Rhino]

Good morning D.

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

It will still make the GIA X grade with the possibility of getting VG in the symmetry. If it is due to azimuth angles however (those slopes in the east/west orientation it will likely stay XXX).

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

Yep.

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

To a degree D. The quality of the IS and ASET images are important to me and how much it correlates to real world observation but only here am I just getting started. There are a host of other questions I want answered before I'm going to move forward with a purchase. Questions such as ... What color is the diamonds hue? What are the graining levels? Are their surface breaching inclusions? Are they open or healed? Are they on the crown, pavilion, girdle or all of the above? etc. etc. etc. There is a lot we can't see from pictures online that can impact the value of a diamond upwards of over 40%.

eta: sorry, posted this question before reading pfunk's thread, can't delete. Pardon me if there are questions that has been addressed there. Reading it now.

No prob.

All the best,
Rhino

 

[Rhino]

Rhino,

Do you have the measurements or sarin data on that AGS ideal ASET that you posted by any chance?

That particular one is all AGS Ideal with proportions of 35.6/41.0 with a 57.9 table. I posted that in response to your request for an AGS Ideal with leakage.

All the best,
Rhino

 

[Rhino]

Gary, what do you refer what's observed on the 3rd and 4th pictures 1/3 down the page?
(where the upper girdle line doesn't align with the pavilion facet line plus there's a ..."clipped portion"?)
And how does it affect performance of the diamond?

Hi D, will try to attach a word doc report - not sure it will work - lets see - no, so I will do a screen shot of the main offenders.
these are very detailed reports - I made the VG factors red. This is not the one GIA uses - because this stone is both GIA XXX (and AGS PGS 0, but i suspect would not qualify for AGS ideal symmetry).
So in answer to your question - there are many things going on and it is possible to identify that this or that is the main offender - but really it is often a complex interaction between a host of factors and facet interplay.

Good example Garry. Nothing matches the Helium Reports for showing the "why's" as to cutting flaws and what needs to be fixed. I would add one caveat that it is not uncommon, even for precision cut H&A's to get "Very Good" in facets sets such as stars and/or upper half angle deviations.

All the best,
Rhino

 

[Rhino]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

Yes, this is the safe approach and is what is generally recommended here for evaluating GIA diamonds. Most stones are cut to the margins of GIA Ex parameters for weight retention purposes. And because the GIA grading system is based upon matching the averaged rounded numbers on the cert to predefined tables, and because facet precision is not accounted for in the system, cutters have quite a bit of lattitude for achieving the GIA EX grade. An ASET image informs you of leakage and other issues, and to an extent facet precision and painting and digging.

Bryan GIA - GTL largely use Helium scanners for rounds with software boundaries developed over time for rounds these days. There are facet precision factors of both azimuth and angle variations. There is an example that you can open from this page:
http://www.octonus.com/oct/products/helium/polish/

I believe visual microscopic evaluation and facet meet points are not as heavily weighted as they once were.

Garry,
You bring up an interesting point. It would be assumed that the GIA would use the most advanced and accurate scanning technology available as part of their take-in and evaluation process. It is known that they will demote an otherwise EX cut to VG if they detect significant painting or digging out. That determination is most likely based largely on the scan, and is reported specifically on the report under comments. So, in this aspect facet precision is taken into account (although there is some disagreement with the overly broad assessment of this penalty).

But the question your post raises is how is the other precision related data used or reflected in a GIA report. That is, if there are deviations in the helium scan that exceed the tolerances imbedded in the helium software, does that affect the GIA grading? And if so, how would a deduction for say deviation in pavilion angles be reflected in a GIA report?

Greetings Bryan,

While GIA certainly has access to the Helium Reports they, nor any lab I am aware of takes into account the strict tolerances laid out in the Helium symmetry grade for each facet set. Were they to even many H&A's would not make the cut as there is more tolerance in say upper half and star facet angles without impacting visuals. For example you can easily have over a 1 degree variation in upper half angles ... say from 40-42 degrees and the diamond still be fine. If the variances however were that wild in say crown or pavilion mains it'd hurt the diamond moreso. On the GIA FacetWare it does take variances into account but not to the degree that Helium does.

Hope this finds you well.

Kind regards,
Rhino

 

[Texas Leaguer]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

Yes, this is the safe approach and is what is generally recommended here for evaluating GIA diamonds. Most stones are cut to the margins of GIA Ex parameters for weight retention purposes. And because the GIA grading system is based upon matching the averaged rounded numbers on the cert to predefined tables, and because facet precision is not accounted for in the system, cutters have quite a bit of lattitude for achieving the GIA EX grade. An ASET image informs you of leakage and other issues, and to an extent facet precision and painting and digging.

Bryan GIA - GTL largely use Helium scanners for rounds with software boundaries developed over time for rounds these days. There are facet precision factors of both azimuth and angle variations. There is an example that you can open from this page:
http://www.octonus.com/oct/products/helium/polish/

I believe visual microscopic evaluation and facet meet points are not as heavily weighted as they once were.

Garry,
You bring up an interesting point. It would be assumed that the GIA would use the most advanced and accurate scanning technology available as part of their take-in and evaluation process. It is known that they will demote an otherwise EX cut to VG if they detect significant painting or digging out. That determination is most likely based largely on the scan, and is reported specifically on the report under comments. So, in this aspect facet precision is taken into account (although there is some disagreement with the overly broad assessment of this penalty).

But the question your post raises is how is the other precision related data used or reflected in a GIA report. That is, if there are deviations in the helium scan that exceed the tolerances imbedded in the helium software, does that affect the GIA grading? And if so, how would a deduction for say deviation in pavilion angles be reflected in a GIA report?

Greetings Bryan,

While GIA certainly has access to the Helium Reports they, nor any lab I am aware of takes into account the strict tolerances laid out in the Helium symmetry grade for each facet set. Were they to even many H&A's would not make the cut as there is more tolerance in say upper half and star facet angles without impacting visuals. For example you can easily have over a 1 degree variation in upper half angles ... say from 40-42 degrees and the diamond still be fine. If the variances however were that wild in say crown or pavilion mains it'd hurt the diamond moreso. On the GIA FacetWare it does take variances into account but not to the degree that Helium does.

Hope this finds you well.

Kind regards,
Rhino

Hello Rhino,
Your last statement is the essence of what I was trying to get to. As Garry points out the GIA does a very sophisticated and accurate scan of every diamond it takes in. And certain data from the scan is used in the process of rendering a cut grade. However, unlike the AGS Light Performance grading process, the actual scan or 3D model of the diamond is not ray traced. Certain basic data is extracted, averaged and rounded and then matched to predefined tables in order to determine a grade on their scale.

We also know that the AGS system and the Ideal grade, as strict as it is, is also forgiving of a certain level of performance deficits and that facet precision is not a specific factor in the analysis (although serious faults would affect the other performance scores and be indirectly accounted for).

So, my question is, since the helium scan is a standalone piece of the GIA grading process, what info do they take from that and how is it used? And if there is a deviation that dings the grade when all the rounded averages land in the tables for EX, how is the downgrade reported?

 

[Serg]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

Yes, this is the safe approach and is what is generally recommended here for evaluating GIA diamonds. Most stones are cut to the margins of GIA Ex parameters for weight retention purposes. And because the GIA grading system is based upon matching the averaged rounded numbers on the cert to predefined tables, and because facet precision is not accounted for in the system, cutters have quite a bit of lattitude for achieving the GIA EX grade. An ASET image informs you of leakage and other issues, and to an extent facet precision and painting and digging.

Bryan GIA - GTL largely use Helium scanners for rounds with software boundaries developed over time for rounds these days. There are facet precision factors of both azimuth and angle variations. There is an example that you can open from this page:
http://www.octonus.com/oct/products/helium/polish/

I believe visual microscopic evaluation and facet meet points are not as heavily weighted as they once were.

Garry,
You bring up an interesting point. It would be assumed that the GIA would use the most advanced and accurate scanning technology available as part of their take-in and evaluation process. It is known that they will demote an otherwise EX cut to VG if they detect significant painting or digging out. That determination is most likely based largely on the scan, and is reported specifically on the report under comments. So, in this aspect facet precision is taken into account (although there is some disagreement with the overly broad assessment of this penalty).

But the question your post raises is how is the other precision related data used or reflected in a GIA report. That is, if there are deviations in the helium scan that exceed the tolerances imbedded in the helium software, does that affect the GIA grading? And if so, how would a deduction for say deviation in pavilion angles be reflected in a GIA report?

GIA symmetry gradings system has 2 parts: Objective ( as Facetware) and Subjective ( from grader Who grades visual asymmetry).

final grade can not be better than Facetware grade. Grader can only reduce grades.
To guaranty that diamonds will receive EX if it has grade EX in HP, we added many parameters in HP reports with very strict thresholds.
So all( may be 99,99% diamonds ) with HP EX grade will receive GIA EX ( symmetry grade) and even many HP VG diamonds will also receive GIA Ex grade.
we did it several years ago. I think now cutters use more soft thresholds in HP( 1st thresholds HP version was to strict because we had not real statistic )/
GIA EX grade system and HP EX grade system are not same. We did not use any information from GIA to develop it.( except diamonds with GIA EX and GIA VG symmetry grades)

 

[Texas Leaguer]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

Yes, this is the safe approach and is what is generally recommended here for evaluating GIA diamonds. Most stones are cut to the margins of GIA Ex parameters for weight retention purposes. And because the GIA grading system is based upon matching the averaged rounded numbers on the cert to predefined tables, and because facet precision is not accounted for in the system, cutters have quite a bit of lattitude for achieving the GIA EX grade. An ASET image informs you of leakage and other issues, and to an extent facet precision and painting and digging.

Bryan GIA - GTL largely use Helium scanners for rounds with software boundaries developed over time for rounds these days. There are facet precision factors of both azimuth and angle variations. There is an example that you can open from this page:
http://www.octonus.com/oct/products/helium/polish/

I believe visual microscopic evaluation and facet meet points are not as heavily weighted as they once were.

Garry,
You bring up an interesting point. It would be assumed that the GIA would use the most advanced and accurate scanning technology available as part of their take-in and evaluation process. It is known that they will demote an otherwise EX cut to VG if they detect significant painting or digging out. That determination is most likely based largely on the scan, and is reported specifically on the report under comments. So, in this aspect facet precision is taken into account (although there is some disagreement with the overly broad assessment of this penalty).

But the question your post raises is how is the other precision related data used or reflected in a GIA report. That is, if there are deviations in the helium scan that exceed the tolerances imbedded in the helium software, does that affect the GIA grading? And if so, how would a deduction for say deviation in pavilion angles be reflected in a GIA report?

GIA symmetry gradings system has 2 parts: Objective ( as Facetware) and Subjective ( from grader Who grades visual asymmetry).

final grade can not be better than Facetware grade. Grader can only reduce grades.
To guaranty that diamonds will receive EX if it has grade EX in HP, we added many parameters in HP reports with very strict thresholds.
So all( may be 99,99% diamonds ) with HP EX grade will receive GIA EX ( symmetry grade) and even many HP VG diamonds will also receive GIA Ex grade.
we did it several years ago. I think now cutters use more soft thresholds in HP( 1st thresholds HP version was to strict because we had not real statistic )/
GIA EX grade system and HP EX grade system are not same. We did not use any information from GIA to develop it.( except diamonds with GIA EX and GIA VG symmetry grades)

Serg,
Thank you for the insight on how you developed the reports regarding GIA grades and your thresholds.

As I understand it GIA is using your helium scanner. Are they using your reports also, or just the measurements derived from the scan and their own proprietary reports? What data are they parsing and how are they using it?

We know that they have a specific penalty for painting and digging out. Are there other deviations that will result in scan driven downgrade? And if so, how do they state it on a report it if everything else qualifies for EX?

 

[Serg]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

Yes, this is the safe approach and is what is generally recommended here for evaluating GIA diamonds. Most stones are cut to the margins of GIA Ex parameters for weight retention purposes. And because the GIA grading system is based upon matching the averaged rounded numbers on the cert to predefined tables, and because facet precision is not accounted for in the system, cutters have quite a bit of lattitude for achieving the GIA EX grade. An ASET image informs you of leakage and other issues, and to an extent facet precision and painting and digging.

Bryan GIA - GTL largely use Helium scanners for rounds with software boundaries developed over time for rounds these days. There are facet precision factors of both azimuth and angle variations. There is an example that you can open from this page:
http://www.octonus.com/oct/products/helium/polish/

I believe visual microscopic evaluation and facet meet points are not as heavily weighted as they once were.

Garry,
You bring up an interesting point. It would be assumed that the GIA would use the most advanced and accurate scanning technology available as part of their take-in and evaluation process. It is known that they will demote an otherwise EX cut to VG if they detect significant painting or digging out. That determination is most likely based largely on the scan, and is reported specifically on the report under comments. So, in this aspect facet precision is taken into account (although there is some disagreement with the overly broad assessment of this penalty).

But the question your post raises is how is the other precision related data used or reflected in a GIA report. That is, if there are deviations in the helium scan that exceed the tolerances imbedded in the helium software, does that affect the GIA grading? And if so, how would a deduction for say deviation in pavilion angles be reflected in a GIA report?

GIA symmetry gradings system has 2 parts: Objective ( as Facetware) and Subjective ( from grader Who grades visual asymmetry).

final grade can not be better than Facetware grade. Grader can only reduce grades.
To guaranty that diamonds will receive EX if it has grade EX in HP, we added many parameters in HP reports with very strict thresholds.
So all( may be 99,99% diamonds ) with HP EX grade will receive GIA EX ( symmetry grade) and even many HP VG diamonds will also receive GIA Ex grade.
we did it several years ago. I think now cutters use more soft thresholds in HP( 1st thresholds HP version was to strict because we had not real statistic )/
GIA EX grade system and HP EX grade system are not same. We did not use any information from GIA to develop it.( except diamonds with GIA EX and GIA VG symmetry grades)

Serg,
Thank you for the insight on how you developed the reports regarding GIA grades and your thresholds.

As I understand it GIA is using your helium scanner. Are they using your reports also, or just the measurements derived from the scan and their own proprietary reports? What data are they parsing and how are they using it?

We know that they have a specific penalty for painting and digging out. Are there other deviations that will result in scan driven downgrade? And if so, how do they state it on a report it if everything else qualifies for EX?

Bryan,
I have not rights to publish information about GIA internal methods. You have to ask GIA directly.
I can share only some information about OctoNus work.

 

[Texas Leaguer]

Thanks, Rhino & pfunk!

Rhino, if you don't mind further questions:
- If a diamond' angle variations are so significant to the point that it causes leakages, given that it possess ideal specs, will the said diamond make it to GIA 3X or AGS 000. (I'm guessing AGS will be stricter than GIA and even then GIA may ding it at least for the symmetry portion)

- That AGS 2 in terms of light performance you showed, will that diamond make it for GIA 3X?

- I've heard about GIA's tendency to round off numbers. How scary is this implication irl? Conversely, if a GIA 3X RB with ideal specs has great IS & ASET images, does that mean the it is safe (i.e. most likely don't display variances that can adversely affect its beauty?). So 3X -> check HCA -> check IS & ASET -> good? if yes, you are done? I'm trying to figure out where to stop to feel "safe", sans our eyes.

Yes, this is the safe approach and is what is generally recommended here for evaluating GIA diamonds. Most stones are cut to the margins of GIA Ex parameters for weight retention purposes. And because the GIA grading system is based upon matching the averaged rounded numbers on the cert to predefined tables, and because facet precision is not accounted for in the system, cutters have quite a bit of lattitude for achieving the GIA EX grade. An ASET image informs you of leakage and other issues, and to an extent facet precision and painting and digging.

Bryan GIA - GTL largely use Helium scanners for rounds with software boundaries developed over time for rounds these days. There are facet precision factors of both azimuth and angle variations. There is an example that you can open from this page:
http://www.octonus.com/oct/products/helium/polish/

I believe visual microscopic evaluation and facet meet points are not as heavily weighted as they once were.

Garry,
You bring up an interesting point. It would be assumed that the GIA would use the most advanced and accurate scanning technology available as part of their take-in and evaluation process. It is known that they will demote an otherwise EX cut to VG if they detect significant painting or digging out. That determination is most likely based largely on the scan, and is reported specifically on the report under comments. So, in this aspect facet precision is taken into account (although there is some disagreement with the overly broad assessment of this penalty).

But the question your post raises is how is the other precision related data used or reflected in a GIA report. That is, if there are deviations in the helium scan that exceed the tolerances imbedded in the helium software, does that affect the GIA grading? And if so, how would a deduction for say deviation in pavilion angles be reflected in a GIA report?

GIA symmetry gradings system has 2 parts: Objective ( as Facetware) and Subjective ( from grader Who grades visual asymmetry).

final grade can not be better than Facetware grade. Grader can only reduce grades.
To guaranty that diamonds will receive EX if it has grade EX in HP, we added many parameters in HP reports with very strict thresholds.
So all( may be 99,99% diamonds ) with HP EX grade will receive GIA EX ( symmetry grade) and even many HP VG diamonds will also receive GIA Ex grade.
we did it several years ago. I think now cutters use more soft thresholds in HP( 1st thresholds HP version was to strict because we had not real statistic )/
GIA EX grade system and HP EX grade system are not same. We did not use any information from GIA to develop it.( except diamonds with GIA EX and GIA VG symmetry grades)

Serg,
Thank you for the insight on how you developed the reports regarding GIA grades and your thresholds.

As I understand it GIA is using your helium scanner. Are they using your reports also, or just the measurements derived from the scan and their own proprietary reports? What data are they parsing and how are they using it?

We know that they have a specific penalty for painting and digging out. Are there other deviations that will result in scan driven downgrade? And if so, how do they state it on a report it if everything else qualifies for EX?

Bryan,
I have not rights to publish information about GIA internal methods. You have to ask GIA directly.
I can share only some information about OctoNus work.

I understand Serg. Thank you.

I do notice that in there website explanation of Facetware, in their section on the reasons why the lab grade may differ from the estimate made by the Facetware tool, they mention 137 measurements. It does not specify which ones they are or how it might relate to faceting precision.

And other than the downgrade for painting and digging out which I have seen on reports, I am not familiar with any other downgrades that would relate to issues that trump the rounded averaged basic measurements such as precision problems resulting from large variances. You certainly see some dramatic precision issues in the light performance images of many GIA Triple Ex stones.

 

[Karl_K]

Rhino,

Do you have the measurements or sarin data on that AGS ideal ASET that you posted by any chance?

That particular one is all AGS Ideal with proportions of 35.6/41.0 with a 57.9 table. I posted that in response to your request for an AGS Ideal with leakage.

All the best,
Rhino

What is more interesting is why that combo gets AGS0.
Patterns are not graded and leakage is weighed as part of contrast.
Get the right ratio of contrast to red and it gets the grade as long as it doesn't hit any of the other dedications like spread, painting, digging etc.