How to get ctw of a colored mounted stone?

[ger100]

Hi,

Can someone point me to a site which shows how to get the ctw of a colored mounted stone? (without removing it from mounting).
I know how to do a diamond from Matlins guide.
Is there anyway to use a percent of the SG of the stone and relate it to that of diamond, perhaps??

Thanks
Ger

 

[colormyworld]

Try this link.

http://www.asia-gems.com/gemstone-weight-calculator.php

 

[ger100]

Looks good. Thanks.