I am looking at certs for a antique cushion cut and some of them have Good for either symmetry or polish. I was wondering how important this is and how it affects light performance. If anyone knows more about this I would love to hear!
Are you looking for actual antiques or new antique-cut stones?
This video highlights the symmetry difference with AVCs and another antique cushion. I'm not sure about more subtle differences, though (good vs. very good). http://www.youtube.com/watch?v=RtFh3Agx3gU
It's all about light performance. Generally in modern / recently cut stones (of either modern or antique flavor) the more concerned they are about cutting for light performance, the more concerned they will be in the quality of the polish and symmetry as well. It's rare to see an ideal cut stone with not-so-good polish and symmetry.
thanks...I have been in touch with Perry but he sent me some stones with just "good" symmetry or polish so I was wondering how important that is or if I should just trust his judgement?
As I understand it, symmetry has to do more with how the facets meet at the corners and less to do with the symmetry across the stone to it's corresponding facet.
If Perry says they are nice I'd believe him. I've never heard of anyone being dissatisfied with a stone from them.
Personally speaking, I would say symmetry is less important than polish. As long as the outline of the diamond isn't "out-of-cushion" shape and you don't detect any glaring issues with your naked eye, it's ok to go down even as low as Good for symmetry.
I can handle "good" on an antique stone, but I expect fine quality newly cut ones to have excellent polish and symmetry, personally. I might consider very good if the cut of the stone was outstanding, though.
I agree with ds, if it's a true antique cushion i'd be ok with a good sym, happy with a vg. But on a new cut cushion, sym has to be vg or better. Though finding an ex sym cushion is not easy.
Polish... unless it's a fair, i'm not to worried about it. Polish is a lot harder to loupe than sym deviations. Plus worse comes to worse you get the stone re-polished, shave off .001 cts off the stone and turn a g into an ex polish. Can't do that on a good sym.