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Old Mine cut diamond weight estimations
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Author:  Rachelle Carswell [ Mon Apr 09, 2018 4:10 pm ]
Post subject:  Old Mine cut diamond weight estimations

Hello Gem experts! Could someone suggest the best formula for estimating the carat weight of old mine cut diamonds where the diamond is set in a closed-back setting?
The diamond is somewhere between a wonkey cushion shape and a slight oval. I took diametres at 4 different points across. The girdle is not visible. Is it best to stick to (average Diametre)squared x Depth(estimated at 61.9% diametre) x SG x 0.0061?

Author:  Barbra Voltaire [ Mon Apr 09, 2018 4:17 pm ]
Post subject:  Re: Old Mine cut diamond weight estimations

Hi Rachelle.
I moved your topic to a more appropriate category.

Author:  Rachelle Carswell [ Mon Apr 09, 2018 8:17 pm ]
Post subject:  Re: Old Mine cut diamond weight estimations

Thank you...:)

Author:  Peters [ Tue Apr 10, 2018 2:48 am ]
Post subject:  Re: Old Mine cut diamond weight estimations

Hi,
It seems your formula incorporate twice SG (also in coefficient - 0,0061):
correct one:
D*D*H*SG*0,00175 (for RB)

for old mine coeficient usually is slightly higher: 0,00185 - 0,0019

Peters

Author:  Rachelle Carswell [ Tue Apr 10, 2018 11:14 am ]
Post subject:  Re: Old Mine cut diamond weight estimations

Thank you Peters...I will give that a try. (yes...my mistake for including the SG twice)

Brilliant!

Author:  Barbra Voltaire [ Tue Apr 10, 2018 12:24 pm ]
Post subject:  Re: Old Mine cut diamond weight estimations

Also, a lot has to do with experience.
Estimating, visually, exactly how deep (or shallow) the diamond may be and making corrections.
Good luck!

Author:  thomas.adamas [ Thu Apr 12, 2018 6:46 pm ]
Post subject:  Re: Old Mine cut diamond weight estimations

Barbra Voltaire wrote:
Also, a lot has to do with experience.
Estimating, visually, exactly how deep (or shallow) the diamond may be and making corrections.
Good luck!


Thanks, Barbra. That is exactly the reason why I insist on inspecting an old mine cut diamond before I provide a loss estimate. I want to look at the pavilion and crown angles, table diameter, chipping and dimensions. I tried the formula thing decades ago and found it was usually inaccurate.

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