Paging Garry Holloway: HCA Question

[kenny]

About 2 months ago this round was graded AGS 0, yet the HCA is 3.4.

Also on the HCA chart you designed, the X is plotted far outside the AGS 0 range, which I thought was that solid white shape.
(The dashed one being GIA's Excellent range.)

Has AGS changed (lowered) their cut standards to include deeper diamonds to compete with GIA's Excellent cut grade, meaning your HCA chart's white AGS outline needs an update?
Have you recently changed the math in the HCA?

Could the specs on the AGS report be typos?
What's up?

Here's the stone: http://www.jamesallen.com/diamonds/I-VS1-Ideal-Cut-Round-Diamond-1493112.asp

 

[Garry H (Cut Nut)]

Interesting Kenny,
the specs check out / line up with the images - Ideal-scope leakage and weak light return from the outer facets in the realistic photo.
Will ask Peter and Jason over at AGSL.

 

[Danielc118]

Same deal with this stone?
http://www.jamesallen.com/diamonds/I-VS1-Ideal-Cut-Round-Diamond-1493112.asp

 

[kenny]

Same deal with this stone?
http://www.jamesallen.com/diamonds/I-VS1-Ideal-Cut-Round-Diamond-1493112.asp

Exact same stone.

Garry invented the HCA and may not have time to open every thread so I started a new thread with Garry's name in the Subject line.
Something may be amiss here, and PS is nice in that we have access to some experts.

 

[Danielc118]

whoops

Cheers mate!

 

[kenny]

No worries.

 

[Garry H (Cut Nut)]

I have a response from Jason Quick, research scientist at AGS Lab:

I double checked our report and there were no typos – the parameters printed on the document are correct and the stone scored a 0.

While this proportion set isn’t included in the 0 range of the AGS cutting guideline charts, it isn’t uncommon for stones with these proportions (41.1/35.2) to receive an AGS 0 cut grade. Because the AGS light performance grade is determined by ray tracing the 3-dimensional scan of the stone, it isn’t possible to generate charts that are 100% predictive. A stone’s parameters can fall within the AGS ideal range and fail to receive an ideal cut grade and vice versa, as in the case of this stone. In short, the ideal ranges in the AGS cutting guideline charts represent the proportion sets that are most likely to receive an ideal light performance grade and thereby serve as useful guidelines for cutters who are seeking ideal cut grades.

Hopefully these comments are useful for clearing up any confusion regarding the AGS cutting guideline charts and their limited applicability for predicting AGS cut grades.

I should add that my more recent understanding is that diamonds with these proportions can have more table fire in the minor facet area's. And that HCA is based on monoscopic study and when people with 2 eyes look at a diamond some areas of leakage on either side just inside the table (on the left and right) can have a good flash seen by one eye. This registers in the mind as good vs the dark zone we would see in a monoscopic view.
So I think it is time I employed a research assistant to redo some of the HCA data.

However I would not be happy with this stone as an HCA excellent because of the weak upper girdle facets.

 

[kenny]

Thank you Garry for pursuing this and reporting back.

May this thread advance cut quality tools and our understanding of good cut.

Danielc118, the round diamond you have on hold at James Allen may prove an historic diamond in the advancement of the technology of cut quality evaluation.

 

[TitanCi]

I had a stone with nearly identical #s (GIA XXX), and I am really not kidding anyone: As I pulled the stone further from my face, I did see black under the table, the "ring of death" if you will. I spent hours upon hours reading all the articles here, GOG's site, Mr Holloway's analysis of stereoscopic views, and I couldn't let those articles fool me: I really did see it. I am left eye dominant, so perhaps that has something to do with it as the stone was probably shifted towards my left eye as I was pulling it away.

I had hundreds of the same pics of the stone and I swear, the middle of the stone acted funny vs the rest of the stone. I've looked up 56 tables with the same CA/PA combo and it gets an AGS 3-4 I believe... This is an interesting discussion!

 

[Garry H (Cut Nut)]

I had a stone with nearly identical #s (GIA XXX), and I am really not kidding anyone: As I pulled the stone further from my face, I did see black under the table, the "ring of death" if you will. I spent hours upon hours reading all the articles here, GOG's site, Mr Holloway's analysis of stereoscopic views, and I couldn't let those articles fool me: I really did see it. I am left eye dominant, so perhaps that has something to do with it as the stone was probably shifted towards my left eye as I was pulling it away.

I had hundreds of the same pics of the stone and I swear, the middle of the stone acted funny vs the rest of the stone. I've looked up 56 tables with the same CA/PA combo and it gets an AGS 3-4 I believe... This is an interesting discussion!

I better change my AKA name. Maybe I am not so nutty?

 

[Karl_K]

I had a stone with nearly identical #s (GIA XXX), and I am really not kidding anyone: As I pulled the stone further from my face, I did see black under the table, the "ring of death" if you will. I spent hours upon hours reading all the articles here, GOG's site, Mr Holloway's analysis of stereoscopic views, and I couldn't let those articles fool me: I really did see it. I am left eye dominant, so perhaps that has something to do with it as the stone was probably shifted towards my left eye as I was pulling it away.

I had hundreds of the same pics of the stone and I swear, the middle of the stone acted funny vs the rest of the stone. I've looked up 56 tables with the same CA/PA combo and it gets an AGS 3-4 I believe... This is an interesting discussion!

I am strongly right eye dominant and I believe you.
Some people don't fit the norm of vision.

 

[TitanCi]

I had a stone with nearly identical #s (GIA XXX), and I am really not kidding anyone: As I pulled the stone further from my face, I did see black under the table, the "ring of death" if you will. I spent hours upon hours reading all the articles here, GOG's site, Mr Holloway's analysis of stereoscopic views, and I couldn't let those articles fool me: I really did see it. I am left eye dominant, so perhaps that has something to do with it as the stone was probably shifted towards my left eye as I was pulling it away.

I had hundreds of the same pics of the stone and I swear, the middle of the stone acted funny vs the rest of the stone. I've looked up 56 tables with the same CA/PA combo and it gets an AGS 3-4 I believe... This is an interesting discussion!

I better change my AKA name. Maybe I am not so nutty?

^Cut Guru, Mr Holloway!

 

[TitanCi]

I had a stone with nearly identical #s (GIA XXX), and I am really not kidding anyone: As I pulled the stone further from my face, I did see black under the table, the "ring of death" if you will. I spent hours upon hours reading all the articles here, GOG's site, Mr Holloway's analysis of stereoscopic views, and I couldn't let those articles fool me: I really did see it. I am left eye dominant, so perhaps that has something to do with it as the stone was probably shifted towards my left eye as I was pulling it away.

I had hundreds of the same pics of the stone and I swear, the middle of the stone acted funny vs the rest of the stone. I've looked up 56 tables with the same CA/PA combo and it gets an AGS 3-4 I believe... This is an interesting discussion!

I am strongly right eye dominant and I believe you.
Some people don't fit the norm of vision.

The eyes don't lie! What they say in the diamond business is true: nothing beats one's eyes in determining if a stone is beautiful or not, but one has to know what to look for. Although I may not know everything about stones, all the technical aspects...but at least I know what to look OUT for!

 

[Karl_K]

The eyes don't lie! What they say in the diamond business is true: nothing beats one's eyes in determining if a stone is beautiful or not, but one has to know what to look for. Although I may not know everything about stones, all the technical aspects...but at least I know what to look OUT for!

Yep, the eye is always the final judge.
The data gets you one with the potential but until you or your loved one live with a diamond for a couple days in your environment you cant be sure it is the one for you or your loved one.
This is true if buying online and true if buying in a local store.

 

[Danielc118]

Thank you very much for chasing this up guys.

I am currently sorting through 100's of alternative's and using the HCA tool more extensively this time.

I'm sure I will put another thread up soon with my choices!

Just waiting to select the diamond before production on the ring can begin