Grading an old cut diamond

[omc111]

I'm sure this question has been asked and answered many times over but I can't seem to find it. Can an oec be evaluated by the same measurements as a modern round brillant? In terms of crown and pavilion? I'm specifically concerned about light leakage. I don't know if this even makes sense but I hope so.

 

[GemFever]

Hi,

Old cuts don't get the same grades for light performance as modern round brilliants do, but certainly all the angles can be measured. Those measurements won't be helpful in determining precise light performance though. You may be able to find out if the stone is too shallow or too deep, that's about it in my understanding.

But, I believe an old cut is treated like a fancy cut, and those can be tested using an ASET tester. You may be able to find more info here (ASET is discussed closer to the bottom of the page):

http://www.goodoldgold.com/Technologies/ReflectorTechnologies/TheVariousReflectorsontheMarketToday/

Also, the old cut experts here have pretty well trained eyes for judging photographs of old cuts. If you have a very good photo of the faceting structure, it may be possible to see whether the stone has the fish-eye or nailhead effect.

I hope this helps!

 

[ruby59]

https://www.pricescope.com/journal/screening_chart_old_european_cut_diamonds

I agree that an old european cut diamond cannot be judged solely by the numbers, and that you need to see some Oec's in person to train your eye. However, the above chart can offer some guidelines.