What percentage of excellent GIA cut diamonds are AGS 0

[treasurehunter]

or within the Ideal proportion ranges

 

[SirGuy]

Well, that's an interesting one. The vast majority of stones are only graded once. Those that are graded twice are often re-graded by the same lab. (Example, having a GIA stone graded in 1989 and sending it back in for a re-certification.) Very few are graded by both GIA and AGS.

I will say GIA "excellent" covers a wider range than AGS0. Some postulate that GIA excellent could be like AGS 0 to 1.0 or 1.5. I can't speak to that sort of comparison. They grade cut differently anyway. AGS uses 3D ray tracing to account for the performance of each individual facet and how they work with each other.

It can be difficult to draw comparisons or conclusions without hard data.

 

[teobdl]

I think trade people like Rhino or Texas Leaguer would have a good handle on this kind of question.

 

[Rhino]

Most are not and there are quite a number, even that fall within the proportional range that do not make Ideal light performance. In AGS' three dimensional cut grading system you can have a 34.5/40.8 crown pavilion combo not make ideal.

 

[treasurehunter]

Rhino, Is that due to factors such as girdle thickness,stars and halves, symmetry , or other factor I cant think of right now

 

[Lorelei]

I think trade people like Rhino or Texas Leaguer would have a good handle on this kind of question.

Absolutely.