ASET and IS question

[Audreyxcalvin]

Hi,
If a round brilliant diamond has a great ASET and IS images (lots of reds, minimal leakage) does it mean that it is excellent/ideal cut, proportioned and will perform well?
Thanks.

 

[skypie]

Not necessarily. It may perform well but not meet certain criteria to be classified as excellent or ideal cut.

 

[Audreyxcalvin]

Im confused so what if it’s only a good cut or very good cut pper GIA, can it still have great aset and IS?

 

[ringo865]

Probably wouldn't have "great" images. No.

 

[rockysalamander]

GIA has a set of ranges for the angles of cutting that diamonds must meet to be considered Excellent. They are looking for an even pattern of bright and dark. The grading also includes design and "craftsmanship". They are not using an ASET like AGS does. So, this is a visual determination of a bunch of factors and the stone must be within specific numeric ranges to get Excellent, VG, etc.

ASET and IS are showing you light return. For good light return, you need balanced angles. You can find stones that are GIA Very Good that still give you good light return. Why? Because they have correctly balanced proportions to align the facets for good light return, but they don't fall within GIA Excellent range. They may have a steep crown and well-paired pavilion angle to compensate.

FYI...Neither ASET or IS tell you anything about the kind of light return...if the stone is brilliant (white light) or firey (colored small flashes).

Maybe one of trade members can chime in. @Karl_K @oldminer @Texas Leaguer @Wink or others.

 

[Karl_K]

I think you covered it very well rockysalamander.
The other consideration would be if it had contrast issues for use in a ring but if the stone is in hand that is simple to check.
Beyond around 1/2 arm length for averaged sized arms are the arrows sill noticeably dark?(grayish is ok around that point but should soon change) If so it might be better in an earring or pendant.