AGS 0 cut - HCA 1.2?

[Splodge2003]

Can anyone explain why this diamond scores AGS 0 for cut, but doesnt do so well on HCA?

http://www.bluenile.com/uk/diamond-search?elem=sub1&filter_id=0&pt=sig&track=rotator1#certViewer_cert_pid=LD03885211|cert_num=1

 

[JulieN]

1.2 is as good as it gets

 

[ChristineRose]

Anything below 2 is a perfect score on the HCA. The HCA is a fairly crude tool compared to the AGS grade. Grades from 0-2 are equal because the various performance factors start to contradict each other at this level.

 

[krisjon]

HCA only predicts possible performance. AGS 0 confirms it. You don't need HCA with an AGS 0 light report, but a 1.2 is a good score and is only further confirmation of ideal cut proportions.

 

[Splodge2003]

Hi all,

Sorry I should have explained a little better. I know a HCA score of 1.2 is good, but it only shows the light return as very good, and I thought AGS triple 0 was as good as it gets?

I'm not sure my link above works so here is the certificate:
http://www.bluenile.com/certs/104057696004.pdf?params=cHJvZHVjdD1CTlVLJnBob25lPTA4MDArMjA2KzExNjAmbGluaz1odHRwJTNBJTJGJTJGd3d3LmJsdWVuaWxlLmNvbSUyRnVrJTJGX0xEMDM4ODUyMTEmc2t1PUxEMDM4ODUyMTEmbGFiPWFnc2wmc2l6ZT0xNjAwJmN1cnJlbmN5PUdCUCY%3D

 

[ecf8503]

The HCA does that on darned near every stone I've ever seen input to it. Dunno.

But you are seriously overthinking this - you don't even need an HCA on an AGS0 because IT'S ALREADY BEEN PROVEN to have ideal light performance.

On GIA XXX that score 2.5 or lower the next step is an idealscope image to assess light return. This AGS has been evaluated by an ASET at AGS as well as their grader's eyes. You really have nothing to worry about.

 

[Gypsy]

Let me see if I can explain this a bit better for you.

The HCA 4 basic data points to make a rudimentary call on how the diamond "may" perform. It's a rough tool.

EACH stone that receives AGS0 has been examined in person and run through a number of tests.

It does not matter if the HCA is 10 on an AGS0.

The HCA is IRRELEVANT on an AGS0. The AGS0 has already confirmed light performance.

If you want to obsess about performance on an AGS0, the HCA is the exact WRONG thing to focus on.

Get an idealscope image of the stone to confirm performance. That's what you can focus on. So what you need is a way to check actual light performance of your actual stone.

That's what an idealscope image does. https://www.pricescope.com/wiki/diamonds/firescope-idealscope
It shows you how and where your diamond is reflecting light, how well it is going at it, and where you are losing light return. That is why you won't see us recommending Blue Nile, as they do not provide idealscope images for their diamonds. James Allen, GOG, BGD, HPD, ERD and WF do.

Although you don't even NEED an idealscope with an AGS0. It's still a better place to focus your attention if you're concerned about performance. Not the HCA.

Got it now?

 

[Splodge2003]

Sorry I didn't mean it to be a silly question, I just haven't looked at AGS stones much so it kind of threw me. I just thought it was weird that it came out different to some GIA stones that had excellent on everything HCA and a score of 0.7 if AGS ideal is supposed to be the best

 

[krisjon]

Also know that .7 isn't necessarily "better" than 1.2 HCA just because it's a lower number.

 

[Gypsy]

Also know that .7 isn't necessarily "better" than 1.2 HCA just because it's a lower number.

the HCA is a pass fail test.

Every score under 2 is the same as any other.

2 and under pass get an idealscope. 2.5 and under maybe, must have idealscope. 2.6 and over fail, don't bother with idealscope.

.7 is NOT better than 1.2. Period.

 

[ChristineRose]

It scores very good on light return because it scores excellent on fire and scintillation. Fire is splitting white light into colored light instead of returning it and scintillation is shifting patterns of dark (no light return) and light (excellent light return). If you want maximal light return, you buy a mirror. After a certain point you have to give up other factors to maximize any one factor.

 

[Gypsy]

It scores very good on light return because it scores excellent on fire and scintillation. Fire is splitting white light into colored light instead of returning it and scintillation is shifting patterns of dark (no light return) and light (excellent light return). If you want maximal light return, you buy a mirror. After a certain point you have to give up other factors to maximize any one factor.

I'm not entirely sure this is true.

the HCA is very harsh on depth. Often the "very good" on light return is because it's being (unduly) prejudicial on depth.

 

[ChristineRose]

Deep stones have more fire and scintillation. When the GIA surveyed people they often preferred the deep stones. Gary argues that the comparison was done under conditions that favored deep stones.

 

[John P]

The VG from HCA in light return is because the 59% Table and 33.1 CA combine for a slightly lower crown than some folks find optimal for balanced brightness and dispersion. If you enter a 58% Table instead, the slight increase in crown height geometry results in 4 EXs. Or change the crown angle to 33.3. Or change the pavilion angle to 40.8 to compensate down there. Viola. It's slight give and take in a metric that does not account for many data points...

What of the 40 minor facets (of 57 total) which are unaccounted-for? How tight is the cut-consistency? What's the degree of 3D optical precision? Was it fashioned with normal indexing? ~ None of this information is present. The HCA is imagining a "chalk outline" of averaged (sometimes rounded) Table, Crown and Pavilion data, and providing you with good information that is intended to be helpful, but not ultimate.

HCA usage warnings here: https://www.pricescope.com/wiki/diamonds/holloway-cut-advisor

In Context

Just imagine that you're trying to get to know someone's looks and personality...

An HCA score is merely like having a chalk outline of the person.
Grading report numbers are like having the person's height, weight and clothing measurements.
An ASET or Ideal-Scope (for RB) image is like having a still photo of the person.
An AGS Platinum "0" in performance is like a panel of judges confirming that the person's personality and looks are solid.
A 3D scan in sophisticated cut-calculation software is like having a video interview with the person.

Eventually, it's a lot of great information. All told it's enough for an experienced cut-specialist to make very detailed performance predictions. But in the end, a live date (dinner & a movie?) will be how you finally judge total personality and looks as you, individually, perceive them.

For this diamond: When you fill in the missing information: Minor facets, cut consistency, optical precision, indexing, etc. there's enough robust 3D geometry that it wasn't penalized in the AGS Platinum Metric, which is quite strict, relatively speaking. Though it remains somewhat wide for certain pedantic folks (cough cough)

I hope this is helpful.

 

[c-k]

John, can I call that a 'Paradox of analysis'....it depends on who is buying dinner

anyway I think your explanation is a great one...thanks

 

[Regular Guy]

LIke


Ira Z.

 

[Gypsy]

HCA information here: https://www.pricescope.com/wiki/diamonds/holloway-cut-advisor

In Context

Just imagine that you're trying to get to know someone's looks and personality...

An HCA score is merely like having a chalk outline of the person.
Grading report numbers are like having the person's height, weight and clothing measurements.
An ASET or Ideal-Scope (for RB) image is like having a still photo of the person.
An AGS Platinum "0" in performance is like a panel of judges confirming that the person's personality and looks are solid.
A 3D scan in sophisticated cut-calculation software is like having a video interview with the person.

Eventually, it's a lot of great information. All told it's enough for an experienced cut-specialist to make very detailed performance predictions. But in the end, a live date (dinner & a movie?) will be how you finally judge total personality and looks as you, individually, perceive them.
.

 

[Roxy]

The VG from HCA in light return is because the 59% Table and 33.1 CA combine for a slightly lower crown than some folks find optimal for balanced brightness and dispersion. If you enter a 58% Table instead, the slight increase in crown height geometry results in 4 EXs. Or change the crown angle to 33.3. Or change the pavilion angle to 40.8 to compensate down there. Viola. It's slight give and take in a metric that does not account for many data points...

What of the 40 minor facets (of 57 total) which are unaccounted-for? How tight is the cut-consistency? What's the degree of 3D optical precision? Was it fashioned with normal indexing? ~ None of this information is present. The HCA is imagining a "chalk outline" of averaged (sometimes rounded) Table, Crown and Pavilion data, and providing you with good information that is intended to be helpful, but not ultimate.

HCA usage warnings here: https://www.pricescope.com/wiki/diamonds/holloway-cut-advisor

In Context

Just imagine that you're trying to get to know someone's looks and personality...

An HCA score is merely like having a chalk outline of the person.
Grading report numbers are like having the person's height, weight and clothing measurements.
An ASET or Ideal-Scope (for RB) image is like having a still photo of the person.
An AGS Platinum "0" in performance is like a panel of judges confirming that the person's personality and looks are solid.
A 3D scan in sophisticated cut-calculation software is like having a video interview with the person.

Eventually, it's a lot of great information. All told it's enough for an experienced cut-specialist to make very detailed performance predictions. But in the end, a live date (dinner & a movie?) will be how you finally judge total personality and looks as you, individually, perceive them.

For this diamond: When you fill in the missing information: Minor facets, cut consistency, optical precision, indexing, etc. there's enough robust 3D geometry that it wasn't penalized in the AGS Platinum Metric, which is quite strict, relatively speaking. Though it remains somewhat wide for certain pedantic folks (cough cough)

I hope this is helpful.

I just liked this analogy so much that I wanted to "repeat" it !