HCA correlation to light performance?

[rstillin]

Okay to Mr. Halloway. I''ve been using the HCA on pricescope to look at a number of diamonds. I particullarly interested in diamonds which score excellent in BR-FR-SC.

My first question:

Are you conducting studies to validate the results of the HCA for Br-Fr-Sc against other tools like Brilliance Scope?

My second question:


Here is a stone that rates ex-ex-vg (the posting by GOG which states ex-vg-vg) and HCA of 1.5

I would expect this stone to not perform as well as ex-ex-ex analysis from HCA. However the Brilliant scope results are VH-VH-VH... a relative rarity according to GoG.

The results of the two seem contradictory.

 

[rstillin]

0.84 G VS2
1.5-EX ex-vg-vg-vg
ags 0
H&A 60.7% 56.5% 34.6° 40.9° 1.11% id id neg 6.106x6.124x3.710 AGS

 

[rstillin]

Factor Grade
Light Return Excellent
Fire Excellent
Scintillation Very Good
Spread
or diameter for weight Very Good
Total Visual Performance 1.5 - Excellent
within TIC range


a second stone:

1.24 E VS1 0.9-EX
ex-ex-ex-vg 0
H&A 61% 55.9% 34.4° 40.7° 1.69% id id mb 6.935x6.964x4.236 AGS

and this one scores H-VH-H on the Brilliantscope score according to GoG.


Lower HCA score, with better predicted results, but not scoring as well on Brilliantscope.

 

[chagall]

I am not a diamond expert, but I was under the impression that HCA is really a rough tool in determing light performance. So a stone that''s < 2.0 will be good, but HCA 0.1 is not necesssary better than 2.0. The Bscope is based on direct real light and is probably more realistic.

 

[belle]

Date: 1/26/2006 12:48:35 PM
Author:rstillin

My first question:

Are you conducting studies to validate the results of the HCA for Br-Fr-Sc against other tools like Brilliance Scope?

hca makes predictions based on known proportions. there are a multitude of factors that can effect the overall performance of a diamond including, but not limited to, minor facets, girdle treatments and deviations in optical symmetry. measurement devices such as bs give reading according to the methodologies imposed by their designer and no two are going to give the same results. to try and validate a tool such as the hca using these programmed devices would be futile.

Date: 1/26/2006 12:48:35 PM
Author:rstillin

My second question:


Here is a stone that rates ex-ex-vg (the posting by GOG which states ex-vg-vg) and HCA of 1.5

I would expect this stone to not perform as well as ex-ex-ex analysis from HCA. However the Brilliant scope results are VH-VH-VH... a relative rarity according to GoG.

The results of the two seem contradictory.

again, there are factors involved in diamond performance that are not factored by the hca. also, keep in mind that the results from bs are not guaranteed repeatable. you could run the stone multiple times and get different results because bs only claims to be accurate +/-5% that in itself could be considered contradictory.

 

[rstillin]

Okay, I buy all that... especially the repeatability of BS.
I have to also be warry of BS results then... I could run the stone three times and get different results e.g. H-VH-VH vs. H-H-VH.

So I see why there is an HCA "score"?
By having a score it implies that the HCA is measuing some subjective quality. 0.9 is closer to the baseline than 1.5 is.

However I do not see why there is a rating of BR-FR-SC if the HCA "score" cannot predict actual light performance.

so the statement:

"The HCA is designed to aid a novice consumer or an experienced trade buyer in selecting unseen diamonds as though each diamond were lined up side-by-side. It describes in simple words how each diamonds appearance to a buyer in a retail sales lighting environment. HCA demerits diamonds with sub-optimal performance, such as light loss out the pavilion, excessive head-shadowing or fisheye effects etc".

This implies that I can compair HCA scores and it''s anagolous to compairing diamonds visual performance.

But what what you''re telling me is that the BR-FR-SC scores are estimations of the visual performance and they may or may not correlate to the actual visual performance?

 

[belle]

Date: 1/26/2006 2:06:34 PM
Author: rstillin

Okay, I buy all that... especially the repeatability of BS.
I have to also be warry of BS results then... I could run the stone three times and get different results e.g. H-VH-VH vs. H-H-VH.

So I see why there is an HCA 'score'?
By having a score it implies that the HCA is measuing some subjective quality. 0.9 is closer to the baseline than 1.5 is.

However I do not see why there is a rating of BR-FR-SC if the HCA 'score' cannot predict actual light performance.

the hca looks at crown angle/table (derived from pavilion and overall depth) to estimate fire.
light return is overall proportions, specifically crown and pavilion angles.
spread is simple weight ratio.
the purpose of hca is not, and will never be, to pick one diamond with good proportions over another. the purpose is, basically, to seperate the wheat from the chaff... to help consumers find stones with proven proportion combinations that are likely to perform well.

Date: 1/26/2006 2:06:34 PM
Author: rstillin

so the statement:

'The HCA is designed to aid a novice consumer or an experienced trade buyer in selecting unseen diamonds as though each diamond were lined up side-by-side. It describes in simple words how each diamonds appearance to a buyer in a retail sales lighting environment. HCA demerits diamonds with sub-optimal performance, such as light loss out the pavilion, excessive head-shadowing or fisheye effects etc'.

But what what you're telling me is that the BR-FR-SC scores are estimations of the visual performance and they may or may not correlate to the actual visual performance?

i am saying that if you want to try and correlate an 'excellent' using one metric against a 'very high' or 'stupendous' or 'higest of high' on another, you are not necessarily going to get the same results. there are just too many other variables. using these proportions, hca CAN predict shallow diamonds, it CAN predict a fish-eye and those factors effect actual visual performance. what it can't do is predict what you will pick as 'beautiful' from an equal line up of well cut stones and it shouldn't be used as such.

 

[valeria101]

The HCA comes from a different line of research about diamond optics than the Brilliance Scope or Isee2.

The closest connection you may find are the AGS cut grades.

There should be a good bunch for you to read about what exactly this background is on Ideal-Scope.com and the OctoNus website.

As far as I know, there is no comparable open research available about the Brilliance Scope or Isee2 - quite easy to understand because of the commercial-only nature of these tools.

Perhaps the commercial bend of the HCA is not totally zero either, but this in only a pretty darn small tip of a rather large Iceberg. So... it can be free of charge. You'll see what I mean...

The question 'how do these grading standards relate' is nothing new... and you may find it takes a while to get to a conclusion. Not surprising, since there seems to be quite a bit of professional effort involved in adding complexity to these grading methods.

Here's another question: does one really need to get to the bottom of this just to buy a diamond? Hopefully not. Some informed executive decision may help in the way. Time has a price too - unless you make a minor 'hobby' of it (like myself).

My 2c

 

[rstillin]

Sorry if I’m being dense or causing frustration. I will not correlate HCA''s excellent to BS''s VH or try to correlate any other tool to HCA analysis. But what I’m getting at is that the HCA score is of 1.5, 2.2, 0.9 etc is not subjective. For a given Pavilion angle, crown angle, total depth, etc there will always be one HCA score. That is because the score is derived from these angles.

However the HCA also tells me on a scale the Brilliance, Fire, and Scintillation of the stone. It rates them by Excellent, Very Good, etc. I realize that these might never be correlated to other tools. I.e. Excellent will not always equal Very High on BS when it comes to Fire. But it seems that I cannot trust that a Excellent brilliance result in the HCA is always better than a Very Good result in the HCA.

Maybe it’s just a misunderstanding on my part, but both tools have relative grading. Very good should always be a step below Excellent. High should always be a step below Very High. But I see stones which rate at the top metric in BS that do not get top in HCA metric for brilliance and vice versa. The reversal in trends leads me to believe that either one or both methodologies for assessing Brilliance are suspect, or the accuracy and precision of the results are suspect.

Belle I looked for your name in the Who''s Who but found nothing. Are you affiliated with the HCA tool somehow? How is it that you are so knowledgeable (and the only person whom ever tries to help me understand this issue I’ve brought up in various different forms)?

 

[rstillin]

I guess to be more succinct, if you are measuring one quality (brilliance) with two different tools (HCA and BS) there should be a correlation, no? I''m not sure how brilliance is defined, but the definitions should be the same for both tools. It would be a ratio of reflected light from a facet, therefore High may not equal Very Good, but High to the 0.7 power = Very Good, or 1.3*High = Very Good.

 

[ecf8503]

This is a tough, deep subject - one not esily answered.

The BS is a tool that some people like, some don''t. It measures light performance under one lighting condition only. And it gives you a result (not always 100% repeatable based on exactly where the bar falls on the sliding scale), but repeatable enough I understand to separate a M/M/M from a H/H/H, for example. The stone may be slightly tilted, etc which can skew the results.

The brilliancescope favors cuts of a certain "style" or "flavor" - whoce facets play nicely with the machinery. Now if they don''t, it doesn''t mean it is a beautiful stone - just that the machine doesn''t favor it.

It''s like food - you may like certain proportions of spices, etc in a dish - and it may not be what someone else does. If you found a "recipe Brilliancescope" somewhere that favored someone else''s taste preferences, would you question yourself about your own ability to taste? Or doubt the preferences of the "recipe BS"?

Some stones are cut for lots of colored light return, big flashes of light, and diminished scintillation - that will show as a "not favorable combination" of bar graph locations in some people''s opinions on the BS. Other people prefer a stone with lots of pinpoint flashes of light - that stone may have a "better" scintillation location on the BS bar graph, but if you don''t like the way it looks what difference does it make? Some cutters also cut for "contrast leakage" - they PLAN for some light leakage under the table for those people who prefer contrast in their stones that is caused by this effect.

I don''t know if this helps or not, as it has taken me years to understand this concept better (there is more to it - stars, LGF''s, etc). I used to be one of those people who looked for across the board VH''s and good symmetery in all light views - to me, that visual was equal to perfection. So I bought one that had that optical signature. Now - having seen an 8* that I love (and whose BS would not look like that at all) side to side with mine, I realize that what my eye perceives as beautiful and what the BS machine does are 2 different things.

Bottom line: You really need to see them. If you can''t, then look at the gem files on GOG''s site for stones with different BS results. Call GOG and have them take some side-by-side pics of differently styled stones so you can get a better feeling of the differences.

Hope that helps -

 

[Regular Guy]

Ross,

I''m putting my light saber down now.

Listen to the force, Ross.

 

[rstillin]

Thank you... there are so many things that I don''t understand in this field. I''m seeing that the definition of brilliance is not necessarily defined the same, or at least the meausurement of it isn''t. Thanks to all who indulge me and try to educate me a little more, it''s not always a trivial excercise

. Please feel free to continue to weigh in on the subject though.

 

[valeria101]

Date: 1/26/2006 5:07:19 PM
Author: rstillin

Thank you... there are so many things that I don't understand in this field. I'm seeing that the definition of brilliance is not necessarily defined the same, or at least the measurement of it isn't.

True. If all those grading systems would agree among themselves, would they still be good for branding and product differentiation?

Well...

Luckily, there seems to be some discernible 'truth' based on tractable science behind the whole mess. It may not be obvious, and for someone like myself with only some limited an unrelated background of applied math & modeling, it has been quite a ride with more dead ends than I would have wished. It would be a serious second job to get to the bottom of these things. And no surprisingly, since there is indeed the professional work of many to generate this information.

My 2c

 

[belle]

Date: 1/26/2006 3:57:42 PM
Author: rstillin

Belle I looked for your name in the Who''s Who but found nothing. Are you affiliated with the HCA tool somehow? How is it that you are so knowledgeable (and the only person whom ever tries to help me understand this issue I’ve brought up in various different forms)?

am i affiliated with hca!? ha! i invented it! ...hca..baloney! it used to be ''bca'' until that aussie rat stole the idea.

hehehe...just kidding of course

i am in no way affliated with hca, i have just spent many an hour (too many an hour!) learning about it for myself. you have ira to thank for laying the ground work on that.

ecf summed it up very well, and you are right...part of the problem is that there is no inherent definition of ''brilliance'' just as there is not one for ''beauty'' and there never will be. hca, of which i have no affiliation

, is a useful tool. it''s not the only tool... there is no ONE device that can tell you what diamond will appeal to your eyes. take each one for what it is without making any one more than what they are capable of.

 

[Garry H (Cut Nut)]

Date: 1/26/2006 3:57:42 PM
Author: rstillin


Belle I looked for your name in the Who''s Who but found nothing. Are you affiliated with the HCA tool somehow? How is it that you are so knowledgeable (and the only person whom ever tries to help me understand this issue I’ve brought up in various different forms)?

Dear Rstillin,

Please read this page thororughly
http://diamonds.pricescope.com/ideal.asp it will give you what you should have read first.

And then if you want to know more please read this http://www.diamond-cut.com.au/ (but that will take a long time).

Please use HCA for rejection (narroewing down selections) and not for any other purpose.

BTW Belle, what time was dinner tonight?

 

[belle]

Date: 1/26/2006 7:48:38 PM
Author: Garry H (Cut Nut)

Dear Rstillin,

Please read this page thororughly
http://diamonds.pricescope.com/ideal.asp it will give you what you should have read first.

And then if you want to know more please read this http://www.diamond-cut.com.au/ (but that will take a long time).

Please use HCA for rejection (narroewing down selections) and not for any other purpose.

BTW Belle, what time was dinner tonight?

same as last night dahling...don't forget to bring that heady cab that you know i love so much

just kidding rstillin!
garry has no idea what kind of wine i like

there is no affiliation


seriously.. those links are required reading. take time to look them over.

 

[Garry H (Cut Nut)]

Date: 1/26/2006 8:06:39 PM
Author: belle

garry has no idea what kind of wine i like

Not true Belle
I know your favorite whine

"no, no, no! Not big enough; you know I like BIG diamonds"