HCA score vs. GIA cut grade?

[kittygirl]

I saw two GIA "very good" (not excellent) cut grade diamonds that look nice to the eyes and score .8EEEVG and 1.1EEEVG on HCA. Should I put more weight on the HCA score or the GIA cut grade?

 

[Brilyant]

I am about as green as you can get, but I think cut is most important.

 

[Regular Guy]

Date: 12/12/2007 2:00:26 PM
Author: Brilyant
I am about as green as you can get, but I think cut is most important.

This is of course the question...but in substance, and fairness...only restates the question.

Buried in the recent wacky thread on the unauthorized tutorial is an alternative answer to the one usually given here.

The GIA grade IS intended to be a cut grade. But...many here think it was not wisely conceived...and that the HCA does, comparably, a better job. My point...one (GIA) is based on clinical trials...and the other, HCA, is perhaps more primarily based on expectations of preference, based on mapping the expectation of how light performs.

Now really...which even sounds better?

Look a second time...the GIA excellent is very big. But...so too is HCA's value of 0 - 2. It is HUGE.

We do have vendors here, very respected...who would I think broadly consider voting for GIA excellent over HCA 0 - 2...but I would prefer to let them speak for themselves on this.

Minimally...because you do have 2 options for considerations of "best looking," you can at least triangulate...compare yourself (i.e., get a GIA excellent and compare...see which you prefer...and vwala...you have either the GIA cut grade, or HCA score to lean on, to argue for your preference. But...if you want to do better than triangulate...there are other resources referred to here. Careful though...as some are simply based on what underpins HCA anyway...so you're just doubling up on your data points.

Regards,

 

[CaptAubrey]

Date: 12/12/2007 1:42:09 PM
Author:kittygirl
I saw two GIA 'very good' (not excellent) cut grade diamonds that look nice to the eyes and score .8EEEVG and 1.1EEEVG on HCA. Should I put more weight on the HCA score or the GIA cut grade?

If you've seen them, I would put more weight on what your eyes tell you.

 

[JohnQuixote]

The Cap'n speaks the truth.

As for PS, there are several cut assessment systems that have teeth here (GIA, AGSL, HCA and AGA).

You'll find that there's a robust area of approval/overlap in the systems, but they don't always agree. You can use pavilion angle to identify where the ‘center’ of the different metrics lies: For 53-58% tables, pavilion angles 40.6-41.0 have the greatest approval cross-system. The AGS cut guidelines suggest most 0 candidates right in that range. The HCA and AGA prefer the shallow side of that - and a bit lower. The GIA system prefers the steeper side - and higher.

This is why the HCA gives thumbs-up to shallow diamonds the GIA system doesn't give EX to, and the GIA places steep diamonds in EX which the HCA rejects. In a general sense you're safe with slightly above 2 on the HCA but it's nice to have as many details as possible on any combo, including an ideal-scope image - which tells far more than numbers do.

Ira makes salient points. Also, if you're interested, here is a similar thread from a while ago.

 

[strmrdr]

what is the table% and cown and pavilion angles?
These stones are a case by case basis...

 

[kittygirl]

H SI2 T: 56% D: 61.5% CA: 34.0 PA: 40.8
H SI2 T: 55% D: 61.5% CA: 36.0 PA: 40.2
These are GIA certs, so numbers are not that precise