Interesting question on Crown and Pavilion Angles...

[bearcub907]

I have spent a lot time reading and learning about diamonds on this forum. Appreciate everyone who has ever posted. I'm purchasing a ring soon and trying to learn as much as I can. So here is my question:

I understand that we want ideal Crown angle 34-34.9 and Pavilion angle 40-40.9. BUT this is an average of the 8 sides. So for example, a diamond can have the pavilion angle = 40.8 on the GIA report, but if this is an average, then some can be well over 40.8 and also under as long as the average is 40.8; like 4 sides 41.8 and 4 sides 39.8 which would average out to 40.8 and appear as the ideal dimension on the GIA report. If this happens, then the diamond would be a dud.
So how do you know without having the idealscope or ASET images? and is this why Symmetry is even more important?

Thank you to everyone!

 

[ecf8503]

You don't knwo - that's precisely why you need the idealscope / ASET images.

Symmetry has to do with meet points of facets, not symmetry of facets across a stone.

 

[Michael_E]

The location of the culet relative to the table, as in centering, is one of the key determinants of visual symmetry and that location is dependent on how close the main pavilion angles are to each other. The example given by the OP would have the culet being noticeably off center in any top down view and this would be obvious in a well done picture. While idealscope and ASET images help with showing symmetry, or angular differences, they really aren't needed to determine that, a good picture will do or louping the stone is good enough for that. Their real use is in telling one where the light is coming from that gets back to your eyes, which is determined by the combination of both crown and pavilion angles and how they interact.