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 Post subject: Old Mine cut diamond weight estimations
PostPosted: Mon Apr 09, 2018 4:10 pm 
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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?


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 Post subject: Re: Old Mine cut diamond weight estimations
PostPosted: Mon Apr 09, 2018 4:17 pm 
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Hi Rachelle.
I moved your topic to a more appropriate category.


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 Post subject: Re: Old Mine cut diamond weight estimations
PostPosted: Mon Apr 09, 2018 8:17 pm 
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Thank you...:)


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 Post subject: Re: Old Mine cut diamond weight estimations
PostPosted: Tue Apr 10, 2018 2:48 am 
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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


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 Post subject: Re: Old Mine cut diamond weight estimations
PostPosted: Tue Apr 10, 2018 11:14 am 
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Thank you Peters...I will give that a try. (yes...my mistake for including the SG twice)

Brilliant!


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 Post subject: Re: Old Mine cut diamond weight estimations
PostPosted: Tue Apr 10, 2018 12:24 pm 
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Also, a lot has to do with experience.
Estimating, visually, exactly how deep (or shallow) the diamond may be and making corrections.
Good luck!


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 Post subject: Re: Old Mine cut diamond weight estimations
PostPosted: Thu Apr 12, 2018 6:46 pm 
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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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