HCA not agreeing with GIA rating - what's going on with this diamond?

[areorui]

I was seriously considering this diamond: https://www.jamesallen.com/loose-di...-color-vvs2-clarity-excellent-cut-sku-4466861



Its cut is rated Excellent by IGI, and HCA gives it a score of 0.8. However, when I put in the angles into GIA/AGS cut estimator, it gives a rating of Very Good. It looks like the crown angle is too shallow.


Here're the numbers:
Size: 2.13 carat
Color: I
Clarity: VVS2
Depth: 59.6
Table: 58
Crown: 32.9
Pavilion: 40.7

My question is: why does HCA give it such a good rating when GIA/AGS would not? Do you think the shallow crown angle in this diamond would negatively affect its light performance (I know it would be more brilliance and less fire, but is it even ideal for brilliance?)

 

[flyingpig]

You see AGS and GIA grading are different. Likewise, HCA is different from AGS and GIA. In general (over simplified generalization), GIA favors deep stones and HCA favors shallow stones and AGS sits somewhere in between. You can see this in the diagram you posted. The stone you posted is a bit shallow and should excel in light return but suffer in fire and sparkle, in theory, though it should still be a beautiful diamond. I generally recommend a stone whose proportions are GIA X, AGS0 AND HCA less than 2.0.

 

[areorui]

Thanks flyingpig. Give that this stone is too shallow to qualify for GIA X or AGS0, would you not recommend buying it?

 

[flyingpig]

I am ok with shallow stones. In fact, the stone may have a chance for GIA X, depending on the actual angles and how they are rounded. But it is the combination with other factors that make me less thrilled about the stone.
1. It is IGI graded.
2. It is shallow
3. The symmetry is not perfect.
4. VVS is an overkill
5. The price is decent, but not too attractive considering #1 and #2 and #3.

It is still a beautiful stone.

 

[OoohShiny]

when I put in the angles into GIA/AGS cut estimator, it gives a rating of Very Good.

Ooh, I've not heard of that diamondscreener website - looks like it's a Big Data-mining tool, including general pricing history and even individual diamonds!

Very useful, thank you for posting!

 

[areorui]

Ooh, I've not heard of that diamondscreener website - looks like it's a Big Data-mining tool, including general pricing history and even individual diamonds!

Very useful, thank you for posting!

No problem! Glad to help.

 

[areorui]

I am ok with shallow stones. In fact, the stone may have a chance for GIA X, depending on the actual angles and how they are rounded. But it is the combination with other factors that make me less thrilled about the stone.
1. It is IGI graded.
2. It is shallow
3. The symmetry is not perfect.
4. VVS is an overkill
5. The price is decent, but not too attractive considering #1 and #2 and #3.

It is still a beautiful stone.

Hi flyingpig, can you please elaborate on the symmetry? What are you looking for when judging whether the symmetry is perfect or not?

 

[gm89uk]

There is some inconsistent illumination of the arrows, they are not all deep black, but two are slightly lighter. This could photography issue/or symmetry. The table reflections at around 10oclock are not very symmetrical (black bits between the arrows). There is some asymmetry in the half pavilion mains.

But it's not that bad!

 

[areorui]

There is some inconsistent illumination of the arrows, they are not all deep black, but two are slightly lighter. This could photography issue/or symmetry. The table reflections at around 10oclock are not very symmetrical (black bits between the arrows). There is some asymmetry in the half pavilion mains.

But it's not that bad!

Thank you! That's super helpful

 

[Garry H (Cut Nut)]

HCA is the only garding system that gives a bonus for larger spread.

 

[areorui]

HCA is the only garding system that gives a bonus for larger spread.

Thanks Gary. I think it's smart to do that. For the weight, this diamond has a much larger diameter than others, which I really like. What do you think about the shallowness of this stone? Should it deter me from buying, balanced against its good attributes?

 

[Garry H (Cut Nut)]

Thanks Gary. I think it's smart to do that. For the weight, this diamond has a much larger diameter than others, which I really like. What do you think about the shallowness of this stone? Should it deter me from buying, balanced against its good attributes?

When you look closely at the stone it will go darker than deeper stones. If that worries you dont get too close!
But why an off color and totally invisible inclusions - why not jump up to +G and VS2?

 

[areorui]

Great graphic! Thanks for that insight. I bet my girl will be looking at it pretty close all the time, so this worries me.

To answer your question about the color vs cut: I didn't intentionally choose a VVS2 stone. It's just that the better colored stones seem to increase in color a lot. I haven't found an eye clean H/G with the same price...

 

[Garry H (Cut Nut)]

Great graphic! Thanks for that insight. I bet my girl will be looking at it pretty close all the time, so this worries me.

To answer your question about the color vs cut: I didn't intentionally choose a VVS2 stone. It's just that the better colored stones seem to increase in color a lot. I haven't found an eye clean H/G with the same price...

Test her eye sight - if she can focus from 8 inches 20cm or less it could be an issue.
If not from closer than 10-12 inches 25-30cm no problem
I dont have such a problem with IGI, but you will find a big difference droping the clarity. And why is there a big color $$$$ jump - because YOU CAN SEE THE YELLOW