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HCA 0-2 and AGS0

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haagen_dazs

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Hi all
I just wanted to get some furthur clarification.
I know that the HCA is meant as a tool to assist in weeding out not great diamonds.
Generally <2 on the HCA would be the boundary.

I have read that AGS0 gradings are strict.

I was wondering why this diamond graded AGS0 had a HCA of 2.7.

Is this normal/expected that the AGS0 diamonds can be graded with not a "fantastic" HCA score?
The score is not near 2. Its almost about 3.0

Thanks for your input

http://www.jamesallen.com/diamonds/H-SI1-Ideal-Cut-Round-Diamond-1260896.asp
 

kenny

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FWIW this one is right on the edge of the AGS0 range, that solid-white-lined shape below. (GIA's is the dotted line.)

I'd look for one closer to the center, but that's just me.

If you gave me 14 tools that spit out scores I'd try to find a diamond that scored high for every one.
Some people here do not like these tools.
They say trust your eyes.
Two problems with that:
1. The diamonds are thousands of miles away so I can't see them.
2. My eyes may not be experienced and educated.

I like these tools.

1111foiudfg.jpg
 

Lorelei

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Date: 9/25/2009 1:28:06 AM
Author:haagen_dazs
Hi all
I just wanted to get some furthur clarification.
I know that the HCA is meant as a tool to assist in weeding out not great diamonds.
Generally <2 on the HCA would be the boundary.

I have read that AGS0 gradings are strict.

I was wondering why this diamond graded AGS0 had a HCA of 2.7.

Is this normal/expected that the AGS0 diamonds can be graded with not a ''fantastic'' HCA score?
The score is not near 2. Its almost about 3.0

Thanks for your input

http://www.jamesallen.com/diamonds/H-SI1-Ideal-Cut-Round-Diamond-1260896.asp
It scored this way because of the crown and pavilion angles bordering around what we call the steep deep side, this happens sometimes. If you are interested in this diamond an Idealscope image would be the next step.
 

haagen_dazs

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Date: 9/25/2009 1:38:00 AM
Author: kenny
FWIW this one is right on the edge of the AGS0 range, that solid-white-lined shape below. (GIA''s is the dotted line.)


I''d look for one closer to the center, but that''s just me.


If you gave me 14 tools that spit out scores I''d try to find a diamond that scored high for every one.

Some people here do not like these tools.

They say trust your eyes.

Two problems with that:

1. The diamonds are thousands of miles away so I can''t see them.

2. My eyes may not be experienced and educated.


I like these tools.
I like these tools to help me too
Looks like a border line diamond.
Thanks for the input =)
 

Todd Gray

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Date: 9/25/2009 4:10:25 AM
Author: Lorelei
It scored this way because of the crown and pavilion angles bordering around what we call the steep deep side, this happens sometimes.
I have not looked at the specifics of the diamond referenced because forum rules prevent a dealer from commenting on a diamond offered by another dealer so there is no point for me to do so, however I want to provide some insight into the center range that you might want to focus on to increase the HCA score... I like to keep the pavilion angle between 40.6 - 40.9 degrees offset by a crown angle between 34.3 - 34.8 degrees with a total depth between 59 - 61.8% and a table diameter between 53 - 57% and a girdle thickness between thin and medium. Now there are other combinations of crown / pavilion angle that will yield similar visual performance and some experimentation with the HCA will provide insight into what those combinations are likely to be, I''m just trying to provide you with a good place to start your search regardless of which dealer is offering the diamond of potential interest.
 

haagen_dazs

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Date: 9/25/2009 1:20:43 PM
Author: Todd Gray

I have not looked at the specifics of the diamond referenced because forum rules prevent a dealer from commenting on a diamond offered by another dealer so there is no point for me to do so,
ahh that explains why no dealers were commenting on some of my posts
and i was really wanted some insights from all the experts
(and i just found out there is no private messaging system here to get expert help on issues)

what if images but no mention of vendor names or links posted.
can dealers make comments on pure those images and numbers then?
 

haagen_dazs

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wow
this diamond moved fast
1 day after i looked at it and posted and its gone!
 

kenny

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We see that a lot here.

That''s why when getting advice on a stone you should not link to it and don''t post enough info so someone can identify it.
I''d keep the weight color and clarity secret, and change the name on any pics you get from a vendor site to upload here.
The name may have the report number in it.

But we can all recognize by now which vendors many pics come from.
 

Lorelei

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Date: 9/26/2009 12:13:36 AM
Author: haagen_dazs
wow
this diamond moved fast
1 day after i looked at it and posted and its gone!
You will find another better than that one, don''t worry!
 

haagen_dazs

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Date: 9/25/2009 1:28:06 AM
Author:haagen_dazs
Hi all

I just wanted to get some furthur clarification.

I know that the HCA is meant as a tool to assist in weeding out not great diamonds.

Generally <2 on the HCA would be the boundary.


I have read that AGS0 gradings are strict.


I was wondering why this diamond graded AGS0 had a HCA of 2.7.


Is this normal/expected that the AGS0 diamonds can be graded with not a 'fantastic' HCA score?

The score is not near 2. Its almost about 3.0


Thanks for your input


http://www.jamesallen.com/diamonds/H-SI1-Ideal-Cut-Round-Diamond-1260896.asp

hmm to follow up on my original post
here is an example where a diamond (with platinum grading report)
indicates a AGS0 cut grade (including light performance, polish and symmetry)

however it scored a 4.4 on the HCA
(way outside the HCA AGS boundary)

AGS 01040369570005
1.212ct

what gives?



side note, i cannot even see arrows on the computer generated aset image .....
 

Lorelei

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Date: 9/28/2009 2:30:22 AM
Author: haagen_dazs



Date: 9/25/2009 1:28:06 AM
Author:haagen_dazs
Hi all

I just wanted to get some furthur clarification.

I know that the HCA is meant as a tool to assist in weeding out not great diamonds.

Generally

I have read that AGS0 gradings are strict.


I was wondering why this diamond graded AGS0 had a HCA of 2.7.


Is this normal/expected that the AGS0 diamonds can be graded with not a 'fantastic' HCA score?

The score is not near 2. Its almost about 3.0


Thanks for your input


http://www.jamesallen.com/diamonds/H-SI1-Ideal-Cut-Round-Diamond-1260896.asp

hmm to follow up on my original post
here is an example where a diamond (with platinum grading report)
indicates a AGS0 cut grade (including light performance, polish and symmetry)

however it scored a 4.4 on the HCA
(way outside the HCA AGS boundary)

AGS 01040369570005
1.212ct

what gives?



side note, i cannot even see arrows on the computer generated aset image .....
I will look up the report, back shortly.

http://www.agslab.com/reportTypes/pldqr.php?StoneID=01040369570005&Weight=1.212&D=1

It is scoring low because of the steep pavilion angle, images such as Idealscope or ASET are a must with this stone, not often we see AGS0 score that way.
 

Stone-cold11

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Date: 9/28/2009 2:30:22 AM
Author: haagen_dazs
side note, i cannot even see arrows on the computer generated aset image .....
Yap, definitely need an IS/ASET image for that. Where do you see the computer generated ASET image?
 

haagen_dazs

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Date: 9/28/2009 5:36:21 AM
Author: Stone-cold11
Date: 9/28/2009 2:30:22 AM

Author: haagen_dazs

side note, i cannot even see arrows on the computer generated aset image .....

Yap, definitely need an IS/ASET image for that. Where do you see the computer generated ASET image?
isnt the computer generated aset image on the platinium report?
its in the middle lower half

i know the HCA is pretty reliable.
why is it that AGS gave this diamond a 0 ??
that means in their opinion its an excellent diamond!
 

FancyDiamond

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Bumping this thread. I want to know the answer, too. I understand HCA is not an exact prediction, as it is based on only 4 input parameters, assuming perfect symmetry and accurate measurements (small measuement variations across entire stone and small measurement errors). Therefore, I can expect a great performing gem that slightly fails the HCA<2 criterion, but an AGS0 stone that scores over 4 for HCA! Is AGS0 stone not to be trusted as "perfect", as in the case of GIA ExExEx stone?

Dreat find, haagen_dazs!
 

strmrdr

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Interesting diamond.
Remember that a diamond can get ags0 if the performance is there no matter what the numbers.
The problem is not all lighting is taken into account so its not a given it is a great diamond when the system is gamed.

As to why the generated ASET looks better than the number indicate you have to remember that it is the lower half/girdle facets that leak not the mains which is the 41.4 the lowers angle is not given.
Change the lowers angle and you can eliminate the leakage.
That is exactly what was done with this diamond.
80% lgf and some painting of the lowers half facets.
See my article here for more information:

http://journal.pricescope.com/Articles/68/1/Do-the-pavilion-mains-drive-light-return-in-the-modern-round-brilliant.aspx

The cutter of this stone was an absolute genius to game the AGS system in this way. If you go to far with the lower modification AGS will kick it down so balancing the pavilion angle and how much to modify the lowers and still get the grade was hard.
I am impressed they made an AGS4 score 0.

This is in reference to this one:
http://www.agslab.com/pdf_sync_reports/1040369570005-PLDQR.PDF
 

Regular Guy

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Hey, Karl,

I'm a little confusted by what you're saying. I think I'm just not reading you straight, and that you mean only one thing...but to all appearances...you're saying two different things...that...


Date: 9/28/2009 1:00:06 PM
Author: strmrdr
Interesting diamond.

a) Remember that a diamond can get ags0 if the performance is there no matter what the numbers....

and

b) The problem is not all lighting is taken into account so its not a given it is a great diamond when the system is gamed.
noting further that...


Change the lowers angle and you can eliminate the leakage.

but...

The cutter of this stone was an absolute genius to game the AGS system in this way.

and finally

I am impressed they made an AGS4 score 0.
So, I'm like...do you like it?

Would you pay either a fair or discounted price for it, all things being equal, including the fact that you were otherwise shopping for a diamond with those characteristics?
 

Stone-cold11

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maybe, I would have to see it personally. I think the cut is substituting contrast of the main arrows with leakage of the lower halves here.
 

strmrdr

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Date: 9/28/2009 1:47:15 PM
Author: Regular Guy
Hey, Karl,


I'm a little confusted by what you're saying. I think I'm just not reading you straight, and that you mean only one thing...but to all appearances...you're saying two different things...that...



Date: 9/28/2009 1:00:06 PM

Author: strmrdr

Interesting diamond.


a) Remember that a diamond can get ags0 if the performance is there no matter what the numbers....


and


b) The problem is not all lighting is taken into account so its not a given it is a great diamond when the system is gamed.
noting further that...



Change the lowers angle and you can eliminate the leakage.


but...


The cutter of this stone was an absolute genius to game the AGS system in this way.


and finally


I am impressed they made an AGS4 score 0.
So, I'm like...do you like it?


Would you pay either a fair or discounted price for it, all things being equal, including the fact that you were otherwise shopping for a diamond with those characteristics?
RG - I admire the cunning that went into its cutting but it still has the other disadvantages of a deep pavilion.
I would be much happier with a real ags0 without the games
The ags0 cut grade doesn't measure all aspects of diamond performance.
 

Garry H (Cut Nut)

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Date: 9/28/2009 1:00:06 PM
Author: strmrdr
Interesting diamond.
Remember that a diamond can get ags0 if the performance is there no matter what the numbers.
The problem is not all lighting is taken into account so its not a given it is a great diamond when the system is gamed.

As to why the generated ASET looks better than the number indicate you have to remember that it is the lower half/girdle facets that leak not the mains which is the 41.4 the lowers angle is not given.
Change the lowers angle and you can eliminate the leakage.
That is exactly what was done with this diamond.
80% lgf and some painting of the lowers half facets.
See my article here for more information:

http://journal.pricescope.com/Articles/68/1/Do-the-pavilion-mains-drive-light-return-in-the-modern-round-brilliant.aspx

The cutter of this stone was an absolute genius to game the AGS system in this way. If you go to far with the lower modification AGS will kick it down so balancing the pavilion angle and how much to modify the lowers and still get the grade was hard.
I am impressed they made an AGS4 score 0.

This is in reference to this one:
http://www.agslab.com/pdf_sync_reports/1040369570005-PLDQR.PDF
The pavilion facets must be painted and the scan reported numbers do not seem right.
 

haagen_dazs

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AGS#: 10402603
Cut Grade: AGS Ideal 0
Carat Weight 1.175

yet another example of a AGS0 scoring HCA = 3.5

sigh


it says Girdle: Faceted, 1.6% to 4.2%

is this diamond cut to game the system too?
 

haagen_dazs

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AGS#: 10402605
Cut Grade: AGS Ideal 0
Carat Weight 1.293
Light Performance: 0
Polish: Ideal
Symmetry: Ideal

hmmmmm another one with HCA 4.4
 

Lorelei

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Date: 9/30/2009 12:32:13 AM
Author: haagen_dazs
AGS#: 10402603
Cut Grade: AGS Ideal 0
Carat Weight 1.175

yet another example of a AGS0 scoring HCA = 3.5

sigh


it says Girdle: Faceted, 1.6% to 4.2%

is this diamond cut to game the system too?
This one has steep deep angles hence the score but there are things the cutters can do as above to minimize leakage, also as Karl states there are disadvantages to such deep pavilions, images are always a must such as Idealscope to evaluate these diamonds properly. Girdle is fine at thin to medium.

http://www.agslab.com/reportTypes/pldqr.php?StoneID=10402603&Weight=1.175&D=1

Same again with the second diamond, another steep deep, clever cutting again can mimimize leakage in some cases.

http://www.agslab.com/reportTypes/pldqr.php?StoneID=10402605&Weight=1.293&D=1

Images are needed if these are considered for purchase.
 

strmrdr

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As long as cut grading systems have existed there has always been someone pushing the edges and trying to game the system for $$$$.
AGS plat because of the way the grade is calculated is more resistant to this than AGS gold or GIA EX but it is not perfect.
There is no perfect diamond grading tool which is why multiple tools are used.
 

Regular Guy

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Date: 9/28/2009 3:58:34 PM
Author: strmrdr
RG - I admire the cunning that went into its cutting but it still has the other disadvantages of a deep pavilion.
I would be much happier with a real ags0 without the games
The ags0 cut grade doesn''t measure all aspects of diamond performance.
Maybe it would be helpful to name these (other disadvantages).

Obviously, the lower facets manipulation causes some kind of repair.

Is this a paper repair, or real? It''s probably not paper...since we think primarily the measure is of reflector images, no?

If real, what is repaired, and what is not repaired, such that the 0 is positively earned in these cases.

You know...if the only advantage of platinum is the more precise measures, and we only trust good proportions of the major facets, we really don''t need platinum at all, and can just stick with proportion based measures that are satisfactory, and continue to require the more precise non-rounded measures that we have come to expect from AGS.
 

strmrdr

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Date: 9/30/2009 9:45:42 AM
Author: Regular Guy
Date: 9/28/2009 3:58:34 PM

Author: strmrdr

RG - I admire the cunning that went into its cutting but it still has the other disadvantages of a deep pavilion.

I would be much happier with a real ags0 without the games

The ags0 cut grade doesn't measure all aspects of diamond performance.
Maybe it would be helpful to name these (other disadvantages).


Obviously, the lower facets manipulation causes some kind of repair.


Is this a paper repair, or real? It's probably not paper...since we think primarily the measure is of reflector images, no?


If real, what is repaired, and what is not repaired, such that the 0 is positively earned in these cases.


You know...if the only advantage of platinum is the more precise measures, and we only trust good proportions of the major facets, we really don't need platinum at all, and can just stick with proportion based measures that are satisfactory, and continue to require the more precise non-rounded measures that we have come to expect from AGS.
It is real as far as eliminating leakage.
The other effects are many.
1: color entrapment begins to be an issue in that range.
2: can increases the effect of dirt on the diamond
3: has an impact on ETAS and scintillation.
4: has an impact on fire which is related to 5.
5: the largest impact is on contrast patterns.

The largest areas of both white light and fire scintillation are the pavilion mains going from obstruction to returning light.
The deep mains are resistant to obstruction.
In other words the contrast patterns are totaly changed which effects the dynamic contrast and fire.
This change can be seen here:

aset-copy-from-report.jpg
 

Regular Guy

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A wire?

Maybe you could say #5 a little more slowly, Karl.



Date: 9/30/2009 9:58:44 AM
Author: strmrdr

5: the largest impact is on contrast patterns.

The largest areas of both white light and fire scintillation are the pavilion mains going from obstruction to returning light.
The deep mains are resistant to obstruction.
In other words the contrast patterns are totaly changed which effects the dynamic contrast and fire.
This change can be seen here:
Also, the graphic you included...also included on the AGS report...was used...wasn't it?...to establish the zero. Yes?

Also...maybe you can contextualize the value of the purported reduction in leakage...with respect to these other 5 issues you point to. How much concern should we have about these remaining issues, overall?
 

strmrdr

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RG,
To put it simply.
In my opinion the trick cutting that makes it get the ags0 score does not raise it to the same level of the diamonds that we like around here even if it gets the same score from AGS they do.
An Infinity, ACA, gog h&a and other well cut diamonds with no tricks will have eye visible better performance in a lot of lighting.
That is one reason the lab grades are just the starting point around here for selection and not the final answers.
 

Regular Guy

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Karl,

What can I say...you''re lovely to take time out of your day and talk here with me. Would that others might join in here, too, as I raised in response to Judah''s article pinned at the top of the page.

If we were a place that favored the ends vs the means, or the product vs the process, we could tell our readers to fuggedabout it, represent that the pro retailers you have mentioned know how to do their job, thank you very much, so why are you bothering me anyway.

But, traditionally, it''s not how we do things here, really.

I don''t have the original text, but the angle of the HCA...and Pricescope altogether...back when...was as a means to save a little money and get a primo option to boot. Probably we can still do all this.

We''d just like to understand what the heck we''re doing a little better than we do...and not necessarily just leave it to the professionals. Increase the DIY...do it yourself option, ya know...

Regards,
 

strmrdr

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RG, I am not sure what you are looking for.

You wanted an answer and I gave a complex and a very simplified one.
I just listed the diamonds I did because they are a familiar reference and are cut to sweet spots in the AGS0 range rather than being tricked out just to get the grade or pushing the bad side of the grade.
If you clarify what you want to know maybe I can help.

I am a huge fan of diy and always have been :}
 
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