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EXPERT OPINION PLEASE!!

Discussion in 'RockyTalky' started by RICHIII, Jul 11, 2001.

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  1. RICHIII
    Rough_Rock

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    by RICHIII » Jul 11, 2001
    I'm interseted in a RBC GIA graded 1.67 F SI1. The specs are as follows:
    TD=61.3%
    CA=34.4
    CH=15.4%
    PA=40.9
    PD=43.2%
    C=.3
    T=55.3%
    G=1.5%
    7.678(7.64-7.71mm)I beleive 1.8 X,VG,VG,VG is what the cut advisor shows!?
    Is this much of a difference from X,X,X,X because for the amount of money I'm looking to spend I would like the most well-rounded stone, appearance wise possible. Thank you for your replies.
     
    


    


  2. pricescope
    Ideal_Rock

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    by pricescope » Jul 11, 2001
    Hi RICHIII,Based on the data above, there is nothing wrong with this diamond. The stone should be very nice - close to ideal Tolkowsky proportions.Diamonds scoring less than 2 HCA are excellent stones - less than 3% of all diamonds cut in the world.The reason you didn't get all Xs is because slightly deep pavilion. It would score better if pavilion would be 40.5 degrees. However, you might not be able to see the difference.
     
  3. RICHIII
    Rough_Rock

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    by RICHIII » Jul 11, 2001
    Leonid,Thanks for your quick response, that is what I was wondering if to my eye I could tell a difference between the grades on the cut advisor, and I'm sure I can some but if I get a good deal I won't lose any sleep over it. Thanks again
     
  4. pricescope
    Ideal_Rock

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    by pricescope » Jul 11, 2001
    RICHII,HCA < 2 just indicates that there is a very good chance you found an excellent looking diamond.Diamonds with the same HCA score can still look different because of other factors e.g. symmetry.Some people can see the difference after certain practice and time spent staring at their stones [​IMG] It all depends how much obsessed one can get about it [​IMG]If you've got a good deal, please don't loose any sleep but enjoy your diamond! [​IMG]
     
    


    


  5. RICHIII
    Rough_Rock

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    by RICHIII » Aug 5, 2001
    Leonid,
    Same Diamond different rating on the cut advisor. Just by switching to pavillion %(which in this case is 43.2) the advisor reads 1.6 ex,ex,vg,vg. Is this just because all the readings are actually right on the border line of vg & ex? Thanks for all your help and this great site, Rich
     
  6. pricescope
    Ideal_Rock

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    by pricescope » Aug 5, 2001
    RICHIII,Angles are measured more accurately by Sarin. Besides, the girdle can have a different thickness in different points.It is recommended using angles if possible although there is still an error of +/-0.1 degree.Consider HCA as a preliminary filter and once you've got HCA < 2, don't try to split hairs too much. [​IMG]
     
  7. RICHIII
    Rough_Rock

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    by RICHIII » Aug 5, 2001
    Leonid,

    Are all angles read by the machine subject to +/-.1 or only the pavilion? How about table? depth? What if there are averages on the Sarin report in parenthesis does that mean they read the stone multiple times or is it each of the 8 angles read and then averaged? How do I understand all the numbers? I appreciate all your help and patience, Thanks Rich
     
  8. pricescope
    Ideal_Rock

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    by pricescope » Aug 6, 2001
    Rich... good questions [​IMG]+/- 0.1 is for the pavilion angle. Crown angle measurements are less accurate.However pavilion angle is 4-5 times more important because light should be reflected at least twice from the pavilion facets in order to return back to your eyes. If you are interested to learn more about it, check these links: www.cutstudy.com/cut/english/document4.htm , www.diamond-cut.com.au , www.cutstudy.com/cut/english/faceting/ , www.gia.edu/giaresearch/diamond-cut-archive.cfm .
    Another thing is that table, crown and pavilion angles you see in the grading reports are averages from several measurements. Here is an example of the Sarin report: [​IMG] Another example: [​IMG] As you can see, table measurements are taken 4 times, crown and pavilion - 6 times for 6 crown and 6 pavilion facets.In reality each facet can have bad angles but average angle can look good - it is a problem that can be solved only when analyzing measurements for each facet, which may be done in the future. Now you can use HCA as a preliminary filter to separate good from bad. We believe it is still better than systems based on the tolerance to Tolkowsky.
     
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