VG vs EX RB

[SHOWBIZ]

If a RB diamond is GIA graded VG where would that be on the AGS scale?

Just wondering if a VG diamond with HCA score under 1 is worth considering or if GIA VG is too poor of a cut compared to those on the AGS scale.

 

[krisjon]

You don't see many AGS stones beyond a 2 in cut - even thought the scale is 0-10. Most all are 0-1. AGS has the tightest cut specs in the industry, so it's more of and all or nothing approach when a stone is sent their way. Anything that's predictable to be off that 0-1 typically goes to GIA or other labs.

GIA EX is already very broad (and not in a good way) and VG is below that. Comparing that to an AGS ideal is apples and oranges.

Don't sacrifice on cut. And don't rely solely on a HCA score if you can. If you go AGS 0, you don't need HCA, either. It already has proven ideal light return and performance.

 

[c-k]

If a RB diamond is GIA graded VG where would that be on the AGS scale?

Just wondering if a VG diamond with HCA score under 1 is worth considering or if GIA VG is too poor of a cut compared to those on the AGS scale.

Cut is king, the most important part of a beautiful diamond. I would only consider AGSL Ideal cut stones and GIA Ex stones that have Ideal cut angles.

You can compromise on clarity and color, but don't do it on the cut.

 

[diamondseeker2006]

If a RB diamond is GIA graded VG where would that be on the AGS scale?

Just wondering if a VG diamond with HCA score under 1 is worth considering or if GIA VG is too poor of a cut compared to those on the AGS scale.

Cut is king, the most important part of a beautiful diamond. I would only consider AGSL Ideal cut stones and GIA Ex stones that have Ideal cut angles.

You can compromise on clarity and color, but don't do it on the cut.

+1 Not all GIA Excellents are stones I'd buy.

 

[ChristineRose]

GIA cut grade considers many more features than does the HCA. There's a GIA cut estimator. You may find that the estimator gives an excellent and that there was something that knocked your stone down to a VG. For example, poor girdles, large culets, and poor finish would knock a diamond down to VG even though everything in the HCA points a GIA EX.

 

[teobdl]

You need exact numbers. Not all AGS0's fall into GIA Ex. https://www.pricescope.com/tools/hca <--see lower right hand white outline, which represents the AGS 0 candidates for the given table (57%). This area not overlap with the GIA Ex.

Some GIA VG stones could, in fact, qualify as AGS 0. Not likely, but they could.

 

[c-k]

You need exact numbers. Not all AGS0's fall into GIA Ex. https://www.pricescope.com/tools/hca <--see lower right hand white outline, which represents the AGS 0 candidates for the given table (57%). This area not overlap with the GIA Ex.

Some GIA VG stones could, in fact, qualify as AGS 0. Not likely, but they could.

A GIA VG stone qualify for AGS Ideal? Please give details

 

[teobdl]

If you push "go" on the HCA tool, you'll see the graphic. For that table % (and assuming a decent girdle and symmetric cut), the bottom right hand corner of the white outline shows AGS 0 stones that do not overlap with GIA Ex stones (dotted outline).

 

[SHOWBIZ]

thanks everyone, I was always wondering what those shapes were on the HCA graph, now I know. One is for AGS Ideal and one is GIA EX.

The reason I was asking, is cause I found a round GIA VG with these proportions:
0.90ct
VG cut, EX polish, EX symmetry
G color
SI1
62.2% depth, 55% table
35.00 crown angle, 40.6 pavilion angle
slightly thick-thick
no cutlet, no fluorescence
HCA 0.9 and falls within the AGS Ideal white box

 

[teobdl]

That could be a nice stone at a great price. It probably got GIA VG rather than Ex because it has a thick girdle. Note that because the girdle is carrying extra mass, the diamond will not face up as well as an equivalent weight diamond with those same table/pav/crown numbers but thin-medium girdle. In other words, that .9 ct probably has a similar diameter to to a .85 ct diamond or a spready .80.

What is the asking price? It may be priced closer to a .80 ct anyway because of the cut grade.

Can you get an idealscope image? That will help predict light performance.

 

[SHOWBIZ]

it's around $5,000:
http://www.jamesallen.com/loose-diamonds/round-cut/0.90-carat-g-color-si1-clarity-very-good-cut-sku-144473

 

[c-k]

If you push "go" on the HCA tool, you'll see the graphic. For that table % (and assuming a decent girdle and symmetric cut), the bottom right hand corner of the white outline shows AGS 0 stones that do not overlap with GIA Ex stones (dotted outline).

The HCA is a rejection tool to investigate further stones that fall 2.5 - 2 or below. You can't use it to grade diamonds,

 

[krisjon]

Could be a needle in the haystack and worth checking out further. They're few and far between, but they're out there.

 

[John P]

That could be a nice stone at a great price. It probably got GIA VG rather than Ex because it has a thick girdle.

Bingo.

A GIA VG stone qualify for AGS Ideal? Please give details

The center of each system is in a different place. GIA favors deeper combinations and will not award EX to diamonds with PA <40.6. The AGSL system is stricter but its center is shallower than GIA's. Some combinations that can earn AGS 0, depending on overall specifics, will still be excluded from GIA EX if they have <40.6 PA.

 

[SHOWBIZ]

That could be a nice stone at a great price. It probably got GIA VG rather than Ex because it has a thick girdle.

Bingo.

Is there anything really bad about a thick girdle other than it's appearance from close up?

Just want to say thanks again to all the experts for their input. I'm learning so much that I feel like I should open up my own shop soon

 

[krisjon]

Is there anything really bad about a thick girdle other than it's appearance from close up?

You probably won't notice a thicker girdle unless you really scrutinize it, but what it does do is hold extra carat weight in the middle where it doesn't do you any good. But if the price is right and the stone is great otherwise, it's an easy tradeoff.

 

[c-k]

That could be a nice stone at a great price. It probably got GIA VG rather than Ex because it has a thick girdle.

Bingo.

A GIA VG stone qualify for AGS Ideal? Please give details

The center of each system is in a different place. GIA favors deeper combinations and will not award EX to diamonds with PA <40.6. The AGSL system is stricter but its center is shallower than GIA's. Some combinations that can earn AGS 0, depending on overall specifics, will still be excluded from GIA EX if they have <40.6 PA.

I will have to see if I can find the charts of GIA that I thought were current, I sure thought they went as far as 40.2 PA with Cr up in the 35.5 - 36.0 range for an EX. On that same chart I thought that AGSL only went down to 40.4 for AGS0...was I looking at their old system? I may be thinking of something else...thanks