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Pavilion and crown angle advice

Discussion in 'RockyTalky' started by Andrew_Diamondsearch, Aug 19, 2019.

  1. Andrew_Diamondsearch
    Rough_Rock

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    by Andrew_Diamondsearch » Aug 19, 2019
    I’m looking at three different diamonds and would appreciate any assistance / advice. In particular, views on which proportions are best. I’m not sure how significant a difference between 2.8 and 3.8 on HCA tool really is for the average person.

    #1
    1.21 carat; F colour, VS2 clarity, HCA score of 2.8; Crown of 34, Pavilion of 41.2; Table 56% and depth 62.2; Girdle M - ST. No fluorescence

    #2
    1.31 carat; F colour, SI1 clarity, HCA score of 3.5; Crown of 36.5, Pavilion of 40.8; Table 57% and depth 62.8; Girdle M - ST. No fluorescence

    #3
    1.40 carat; F colour, SI1 clarity, HCA score of 3.8; Crown of 35.5, Pavilion of 41; Table 57% and depth 62.7; Girdle ST. No fluorescence

    Thanks for your help
    Andrew
     
    


    


  2. lovedogs
    Ideal_Rock

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    by lovedogs » Aug 19, 2019
    Reject any stones that score over 2 on the HCA. So I would not consider any of them. You can definitely find something much nicer!
     
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  3. lovedogs
    Ideal_Rock

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    by lovedogs » Aug 19, 2019
    If you tell us your budget we can help!
     
  4. tyty333
    Super_Ideal_Rock

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    by tyty333 » Aug 19, 2019
    Ditto @lovedogs ...the crown and pavilion angles are not complimentary and the depth on 2 of the stones is too high. You are most likely losing face up size.
     
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  5. Andrew_Diamondsearch
    Rough_Rock

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    by Andrew_Diamondsearch » Aug 19, 2019
    I have two other options, however this first one is about A$1,500 more than option one and option two, and A$300 more than option three

    Carat 1.33
    Colour F
    Clarity is VS2
    Depth 62.5%
    Pavilion angle 40.8
    Pavilion Depth 43%
    Crown angle 35
    Crown height 16%


    My other alternative appears to have great proportions, but it is strong blue fluorescence (it is therefore the cheapest) and I am concerned what it will look like in direct summer sun (UV index can get to about 12 here).

    Carat 1.30
    E colour
    VS1 clarity
    Pavilion angle 40.6
    Crown angle 34
    Depth 61.7%

     
  6. lovedogs
    Ideal_Rock

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    by lovedogs » Aug 19, 2019
    What is the HCA on these new ones? Under 2?
     
  7. Andrew_Diamondsearch
    Rough_Rock

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  8. lovedogs
    Ideal_Rock

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    by lovedogs » Aug 19, 2019
    Hmmm, I prefer the second one in terms of proportions (because 62.5 + steep crown angle of 35 is risky). But the second one is also a little risky because of the strong fluor and high color (which usually isn't a problem but sometimes can be in rare cases). The high color/strong fluor is usually fine, but easier if someone can confirm it in person.

    Can you get any advanced images (IS/ASET) of either, or can someone confirm that the second one isn't milky or hazy?
     
  9. sledge
    Ideal_Rock

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    by sledge » Aug 20, 2019
    Is it possible to get an ASET or IS image on either of the last 2 stones? That 35/40.8 combo worries me. While it fits in recommended ranges it seems to be hit and miss depending on the precision of the cut. So I see it as risky just going by proportions.

    The 34/40.6 is.combining a shallow crown and shallow pavilion. Normally you want an inverse relationship -- shallow crown/steep pavilion or steep crown/shallow pavilion. It seems shallow combos pull lower HCA scores and anything with HCA of < 1 is sometimes preferred for a pendant or earring. Scores of 1-2 are recommended for e-rings.

    Again, I'd want to see performance images on both stones before committing. Is there a reason why you are limited to these stones? We can likely find you better quality if you provide your budget, color, carat and clarity requirements.
     
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  10. Andrew_Diamondsearch
    Rough_Rock

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  11. Andrew_Diamondsearch
    Rough_Rock

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  12. headlight
    Brilliant_Rock

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    by headlight » Aug 20, 2019
    The photo of the 1 with SBF looks pretty (although I don’t know what it’s optical symmetry is based on a casual photo - diamonds are not easy to photograph - although having “perfect” optical symmetry isn’t life or death for me: sparkle, fire, small table, high crown, none or slight Fluor, where lab report was from, and colorless were my priorities... but I personally would stay away from an E when SBF. I have an E and you are paying a lot for it so why risk it. I know there have been studies, “etc, etc.”, that dispute the issue (yet it was conducted by GIA which I find interesting that anyone here takes stock in it given the distaste here for the GIA research that yielded their Cut Grade System which everyone here thinks yields poor performance and poor makes. So why risk it, don’t go there.
    Also, that stone is mounted... is there a reason? Is a private party selling it (which isn’t a deal breaker).. or was it already mounted by the jeweler? There is a tool (viewer) for which the jeweler can use to assess any negative issues with regard to the SBF. If you really love this stone maybe that would put your mind at ease. Or you can keeep looking, although I do know that finding a nice E that isn’t either with SBF or an undesirable inclusion(s) isn’t so easy to find (hence E color diamonds rarity are less than 1% of all diamonds).
    And yes, I wound also stay away from an HCA of less than 1... everyone says they are more suited for pendants and earrings, yet for me why would you want to limit yourself... I’ve reset many stones and I wouldn’t want to be limited by the potential that it wouldn’t be as desirable in a ring at some point.
    Do you have an IRL photo of the one that had the slightly deeper cut? I’m referring to the 1.33ct. With the HCA score of 1.5.
     
  13. sledge
    Ideal_Rock

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    by sledge » Aug 20, 2019
    I'm not necessarily advocating to ditch a stone because it scores < 1 on the HCA, but rather to be aware of WHY it happens, the true cut quality of the stone and if you are okay with it all.

    I actually bought my wife a BGD stone that scored a 0.7 HCA for her e-ring. Granted, at the time I knew much less about proportions and diamond geometry, and how that plays into the "personality" of a stone. In my case, the stone was cut great and has no problems doing the sparkle bomb dance.

    https://www.briangavindiamonds.com/diamonds/diamond-details/0.867-h-vs2-round-diamond-ags-bl-104098623002

    Capturehca.PNG

    However, looking at the proportions of the stone you can see it has a larger table, shallower crown and medium pavilion which all contribute to the lower HCA score. While these proportions worked on this particular stone, it may not work on another stone with the same proportions. Why? Because WHO cuts the stone and the quality of that cut is equally important. Super ideal vendors like BGD, WF, HPD, VC, etc can get away with pushing typical boundaries because they deal in precision, and push themselves to produce some of the most beautiful stones we've seen. There is a difference when a stone is cut for beauty vs it being cut for weight/profit. But that being said, even within the ideal range it's still that -- a range. Consequently, within a range you end up with variation, personalities, etc.

    My wife's stone had excellent ASET, IS and H&A images to prove the cut is awesome. That said, it's still a personality type. The proportions of this stone means it sizes up very well for the carat weight -- at 6.18 x 6.21 it sizes more like a 0.90+ carat stone. But it also means it favors a little more white light return as well.

    When we eventually upgrade her, we will likely go to D-F color and will seek a small 54-55 table with 62 or less depth and 34.5/40.7, 34.5/40.8 or 35/40.6 combo with 76-77 LGF's and of course H&A precision from a trusted vendor with all the images to give us the warm fuzzies before pulling the trigger. Such a stone will have a "much" different personality in the fact it will favor bigger & bolder rainbow flashes, but come at the expense of that increased dimension for the weight advantage and also a loss of some white light return. Such a stone will probably fall within the 1.3 to 1.7 HCA range as well.

    But in all honesty, when you have actual performance & symmetry images to base your judgement upon, those easily supersede a calculated & estimated HCA score.

    Regardless of the diamond personality you decide upon, I would encourage you to stay within ideal cut proportions and utilize the HCA as a guide. Better yet, if you can get ASET, IS or H&A images then I'd use that data to help make a final decision. Without that data it's just a gamble. For instance I saw a stone last week with near perfect proportions that had leakage showing up in the ASET. The only way that happens is from piss poor cutting. Yet, without those images, one would have been proud to own a stone with those particular proportions.

    So have fun shopping, but do so wisely. :cool2:

    Ideal proportions to target:
    • 54-57 table
    • 60-62.4 depth (prefer < 62)
    • 34-35 crown (maybe 35.5, if paired with a 40.6 pavilion)
    • 40.6-40.9 pavilion (maybe 41, if paired with a 34 crown)
    • 75-80 LGF's
    • Inverse relationship between the crown/pavilion
    • HCA score of 0-2, maybe 2.5-3 if very precisely cut
     
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