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The HCA and the real world

Discussion in 'RockyTalky' started by Greentree, Feb 25, 2002.

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  1. Greentree
    Rough_Rock

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    by Greentree » Feb 25, 2002
    I have made two important (read expensive) diamond purchases in the last several years. In both cases, the manner in which the purchases was made pretty much precluded my use of the HCA..

    Here's the problem: The HCA does not allow the purchaser to evaluate stones on the spot. Both purchases were made in the merchant's store or office. The Internet isn't readily available in this environment. Additionally, in each case the merchant offered a limited number of stones (two, possibly three) for inspection. It's a pick one-or-the-other situation. I think this is done to prevent the customer from getting so involved inspecting stones that he becomes confused, then indecisive, and ends up buying nothing at all.

    The first stone was bought at a respected local jewelry store with my knowing nothing at all about diamonds.. I was pleased with it, but quickly discovered I had bought an "unbalanced" diamond.

    Here are the stats:
    1.03 carats
    6.56-6.68x3.92 mm
    depth percentage 58.7 - 59.8
    table percentage 66
    girdle thin to medium faceted
    culet small
    polish very good
    sym good
    clarity vvs-1
    color I
    flour. medium blue.

    One tutorial described this diamond to be "upside down" --excellent in the less important catagories and good to fair in the more important catagories.

    Before purchasing the second stone, I read all the tutorials on the Internet and resolved to do a better job of selecting a stone. I told the broker I wanted a "balanced" stone of about 2 cts, color no worse than I, clarity no worse than VS2, and a decent, but not necessarily ideal cut. A few days later he had two stones for me to look at. The one I picked was:

    2.04 carats
    8.18-8.13x5.01mm
    Total depth 61.4%
    Table width 59%
    Crown Height 15%
    Pavilion Depth 44%
    Girdle thin, faceted
    Polish VG
    Symmetry VG
    Culet none
    Clarity VS2
    Color I
    Flour. Very Slight

    Comments: "PREMIUM CUT" - The proportions of this diamond are within the tolerance of those of the Premium Cut, thus achieveing a harmonious balance between proportions & the display of brilliance.

    The old style GIA cert on the first stone did not have crown or pavillion data in either percent or degrees. The HCA couldn't tell me much about this stone. The second stone had a new EGL cert that did give crown and pavillion percentages and stated in the comments that the stone was regarded to be "premium cut". The HCA rated the first stone "do not buy" because of its 66% table. The second stone rated 4.2 which evidently Holloway considers to be just an "OK" cut and not a premium cut. Well, I -did- tell the broker it didn't necessarily have to be an ideal cut But I was hoping the HCA would grade it better than that. I really like the stone, though, and, besides, my wife doesn't know the HCA from the NBA!

    Suppose all certificates had the crown and pavilion angles listed and suppose the HCA program was made available for download into a PDA. I could have evaluated the stones in real-time and decided not to buy or argued for a better price. Nevertheless, I don't think either merchant would have been content to bring out stone after stone while I plugged their statistics into the PDA. I would have been politely escorted to the door.

    It looks more and more like GIA is going to have to rate cut just like it does clarity, color, and all the rest. AGA certed stones are not all that common and the EGL's cut evaluation is evidently too generous. Until then, recognizing a well cut stone will continue to depend upon the diamond buyer's experience. This level of experience is something a diamond consumer like myself can never hope to achieve. I have inspected perhaps a half dozen stones in my entire life!

    Cheers,
    :wink2:
     
    


    


  2. pricescope
    Ideal_Rock

    Messages:
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    by pricescope » Feb 25, 2002
    Hi GreenTree :)

    Good observations.

    Here's the problem: The HCA does not allow the purchaser to evaluate stones on the spot

    Ideal-Scope is the easiest solution to this problem.

    We also have a desktop version. Would you buy it? :)) Next version of DiamondCalc ($280) will allow to analyze diamond performance such as light leakage, light return, contrast and in the future fire and scintillation.

    The first stone was bought at a respected local jewelry store with my knowing nothing at all about diamonds.. I was pleased with it, but quickly discovered I had bought an "unbalanced" diamond.

    What is “unbalanced” diamond? :-o Sounds like another Fred Q. term… I believe it is all the matter of personal taste and whether you feel comfortable with the 4C of your diamond.

    Comments: "PREMIUM CUT" - The proportions of this diamond are within the tolerance of those of the Premium Cut, thus achieveing a harmonious balance between proportions & the display of brilliance.

    Premium cut is EGL term – very questionable. EGL also have very wide range for “Tolkowsky Ideal”.

    44% pavilion depth sounds deep and will allow quite a bit of the light leakage penalizing by HCA. However, using pavilion and crown depth % is not accurate especially when they’re rounded as on EGL or HRD reports.

    It looks more and more like GIA is going to have to rate cut just like it does clarity, color, and all the rest. AGA certed stones are not all that common and the EGL's cut evaluation is evidently too generous. Until then, recognizing a well cut stone will continue to depend upon the diamond buyer's experience. This level of experience is something a diamond consumer like myself can never hope to achieve. I have inspected perhaps a half dozen stones in my entire life!

    GIA is going provide more information on cut and will come up with cut grading system in the future. We’ll see how good it’ll be.

    :)
     
  3. buttercup
    Rough_Rock

    Messages:
    87
    Joined:
    Feb 19, 2002
    by buttercup » Feb 25, 2002
    a palm version of the HCA...great idea!
    garry?

    or even better...a palm version of diamcalc

    hey, if i can have the entire Physician's Desk Reference on my Palm, with every single prescription drug made and the appropriate dosing for particular disease states, I think it's totally possible to make a palm program for the diamond-obsessed!

    oh...look what i found...too funny.
    http://arctic.pda.tucows.com/palm/preview/47769.html
     
  4. pricescope
    Ideal_Rock

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    by pricescope » Feb 25, 2002
    Garry is traveling now arround the world :)

    We should meet and ski in Whistler at the end of March.

    Good idea about palm version though - maybe one day when I'll have nothing else to do :tongue:
     
    


    


  5. pricescope
    Ideal_Rock

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    by pricescope » Feb 25, 2002
    BC, did you try this price calculator? Great idea indeed!..
     
  6. Greentree
    Rough_Rock

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    Feb 24, 2002
    by Greentree » Feb 25, 2002
    Oh, I see what you mean, Leonid. If I reduce the pavilion percentage to 42 and increase the crown percentage to 16, I get an HCA rating of 1.0, which is very good. The program must be very sensitive to small changes in crown and pavilion percentages. I think this is because of round-off errors occurring when you do the trigonometry to change the percentages to angles. An error of just a fraction of a percent can make a big difference. No wonder you prefer the measurements expressed as angles. Hmm, the IdealScope looks like a good alternative although it can't give you the quantitative result of the HCA. Also, it requires some practice to understand just what you're looking at. The HCA is just plug and chug.

    DiamondCalc looks like an interesting program. Trouble is I've already blown my budget on gems for this year. Don't know when I'll be in the market again.:))
     
  7. buttercup
    Rough_Rock

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    by buttercup » Feb 25, 2002
    greentree-
    i'm glad you brought up the whole angles percentages thing. i've had a question about that i've been meaning to ask.
    i don't understand why angles are better, is it solely the rounding thing, or is there something else to it?

    leonid-
    could you do me a HUGE favor and show me what the idealscope might look like for this AGA 2A?

    1.89ct
    8.04-7.94x4.84
    Depth: 60.6%
    Table: 58%
    Crown: 13.4%
    Pav: 42.8%
    Cul: none
    HCA 0.3 Ex

    now these crown and pavilion numbers aren't rounded, would angles be that much more accurate still? in playing with the HCA a little, the only difference seems to be if I change the crown to 13.3, then it becomes a BIC instead of a TIC. Will it really make that much of a difference visually? i thought the pavilion made more of a difference than the crown.

    One more idealscope, if you don't mind:
    another AGA 2A

    1.62ct
    7.74-7.79mm x 4.51mm
    Girdle: thin 2.5% faceted
    Culet: pointed
    Table Width(%): 60
    Crown height(%): 13
    Crown angle: 34
    Pavilion Depth(%): 42.5
    Pavilion angle: 40.5
    Depth(%): 58.1
    HCA 0.4 TIC

    Neither of these stones are 'ideal' but if they are cut symmetrically, do you think it might be possible to see arrows with the naked eye? I know nice arrows only happens with certain crown/pavilion/table relationships, but i don't remember where i saw that.
    Thanks so much!!!!!
     
  8. Garry H (Cut Nut)
    Super_Ideal_Rock
    Trade

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    by Garry H (Cut Nut) » Feb 25, 2002
    sleeples flight to HK :(

    I will not do the first stone unless you get angles. Trust me please.
    The second stone looks good - but the crown angle is 13.5% not 13%. Dont use %, especially for pavilon.

    Rcky HK.jpg
     
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