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HCA 0-2 and AGS0

Discussion in 'RockyTalky' started by haagen_dazs, Sep 24, 2009.

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  1. haagen_dazs
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    by haagen_dazs » Sep 24, 2009
    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
     
    


    


  2. kenny
    Super_Ideal_Rock

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    by kenny » Sep 24, 2009
    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
     
  3. Lorelei
    Super_Ideal_Rock

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    by Lorelei » Sep 25, 2009
    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.
     
  4. haagen_dazs
    Brilliant_Rock

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    by haagen_dazs » Sep 25, 2009
    I like these tools to help me too
    Looks like a border line diamond.
    Thanks for the input =)
     
    


    


  5. Todd Gray
    Brilliant_Rock
    Trade

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    by Todd Gray » Sep 25, 2009
    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.
     
  6. haagen_dazs
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    by haagen_dazs » Sep 25, 2009
    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?
     
  7. haagen_dazs
    Brilliant_Rock

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    by haagen_dazs » Sep 25, 2009
    wow
    this diamond moved fast
    1 day after i looked at it and posted and its gone! [​IMG]
     
  8. kenny
    Super_Ideal_Rock

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    by kenny » Sep 25, 2009
    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.
     
  9. Lorelei
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    by Lorelei » Sep 26, 2009
    You will find another better than that one, don''t worry!
     
  10. haagen_dazs
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    by haagen_dazs » Sep 27, 2009

    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?[​IMG][​IMG][​IMG]


    side note, i cannot even see arrows on the computer generated aset image .....[​IMG][​IMG][​IMG]
     
    


    


  11. Lorelei
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    by Lorelei » Sep 28, 2009
    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.
     
  12. Stone-cold11
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    by Stone-cold11 » Sep 28, 2009
    Yap, definitely need an IS/ASET image for that. Where do you see the computer generated ASET image?
     
  13. haagen_dazs
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    by haagen_dazs » Sep 28, 2009
    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!
     
  14. haagen_dazs
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  15. FancyDiamond
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    by FancyDiamond » Sep 28, 2009
    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!
    [​IMG]
     
    


    


  16. strmrdr
    Super_Ideal_Rock

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    by strmrdr » Sep 28, 2009
    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
     
  17. Regular Guy
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    by Regular Guy » Sep 28, 2009
    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...


    noting further that...


    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?
     
  18. Stone-cold11
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    by Stone-cold11 » Sep 28, 2009
    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.
     
  19. strmrdr
    Super_Ideal_Rock

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    by strmrdr » Sep 28, 2009
    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.
     
  20. Garry H (Cut Nut)
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    by Garry H (Cut Nut) » Sep 28, 2009
    The pavilion facets must be painted and the scan reported numbers do not seem right.
     
  21. haagen_dazs
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    by haagen_dazs » Sep 29, 2009
    AGS#: 10402603
    Cut Grade: AGS Ideal 0
    Carat Weight 1.175

    yet another example of a AGS0 scoring HCA = 3.5

    sigh
    [​IMG][​IMG]

    it says Girdle: Faceted, 1.6% to 4.2%

    is this diamond cut to game the system too?
     
  22. haagen_dazs
    Brilliant_Rock

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    by haagen_dazs » Sep 29, 2009
    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
     
  23. Lorelei
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    by Lorelei » Sep 30, 2009
    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.
     
  24. strmrdr
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    by strmrdr » Sep 30, 2009
    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.
     
  25. Regular Guy
    Ideal_Rock

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    by Regular Guy » Sep 30, 2009
    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.
     
  26. strmrdr
    Super_Ideal_Rock

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    by strmrdr » Sep 30, 2009
    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
     
  27. Regular Guy
    Ideal_Rock

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    by Regular Guy » Sep 30, 2009
    A wire?

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



    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?
     
  28. strmrdr
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    by strmrdr » Sep 30, 2009
    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.
     
  29. Regular Guy
    Ideal_Rock

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    by Regular Guy » Sep 30, 2009
    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,
     
  30. strmrdr
    Super_Ideal_Rock

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    by strmrdr » Sep 30, 2009
    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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