Is an GIA Triple EX with proportions that fall AGS Ideal range guaranteed to be AGS 000 quality?

[dumbo]

In looking at diamonds, so many are graded by GIA and not AGS. With that said, using the AGS ideal table charts, we can see which diamonds would qualify for AGS Ideal cut standards. Doing so opens up a lot more choices for diamond shopping; even many of the best cut stones seem to get graded by GIA for whatever reason. Probably because consumers won't appreciate the more stringent AGS rating, even if the same stone were rated AGS 000.

Obviously GIA uses different cut guidelines, but assuming the symmetry and polish on a GIA stone are EX, is there any reason that a GIA with AGS Ideal cut number wouldn't be an AGS Ideal cut rated stone if graded by AGS?

Asking a different way, are there other factors besides cut angles and symmetry/consistency of those angles that AGS uses when evaluating cut?

 

[MissGotRocks]

With AGS, you got accurate angle percentages. GIA rounds their numbers. Now that the two labs have merged, you get cut numbers from GIA which are rounded, and an AGS light performance report. Therefore, you can’t use the old AGS ideal table charts. AGS may have had a 34.8 crown angle which is now rounded to 35 by GIA. Many GIA diamonds with 34.5 crown and 40.8 pavilion angles for example, are not those actual numbers but have been rounded. The AGS light performance grade gives you some assurance about a diamond’s light performance but GIA crown/pavilion angles are just rounded numbers. I would always want to see an IS or ASET image (hopefully both) for any diamond I was considering purchasing. I would never just blindly assume.

 

[DejaWiz]

^ MissGotRocks said it all - the proportions listed on a GIA report are averaged and rounded in a manner differently than what AGS did (not to mention the added 3D assessment of light performance performed), so great numbers on a report don't guarantee AGS000 equivalent cut precision and optical performance.

 

[tyty333]

And just to be clear about AGS000, there are AGS000 stones out there that dont past the muster IMO.

A quick example...this is a 34.2/40.7. Hopefully its just a matter of making sure the angles are a more complementary
combination...

4.64 Carat round diamond

This 4.64 carat round diamond H color si1 clarity has Ideal proportions and a diamond grading report from AGS

www.jamesallen.com

 

[dumbo]

OK, thanks for the guidance!

So:

Narrow it down with measurements but know that GIA measurements can be rounded and may not be accurate

Get a ASET or Idealscope image to confirm light performance

 

[denverappraiser]

AGSL is no longer in business. They have licensed some of their system to GIA who are offering a 'supplemental' report that they call 'AGS Ideal Report by GIA'. It's similar, but not identical, to what AGS would have told you pre-2022, including a digitally generated ASET image. The differences are in some of the outliers. 000, as AGSL did it, was not a subset of xxx, nor was it intended to be. In the new system it is. To be eligible for the supplemental GIA report, a stone must first be xxx.

AGS Ideal® Report by GIA

AGS Ideal^® Report by GIA

www.gia.edu