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Trying to understand the HCA just a little better....

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aljdewey

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Date: 11/10/2005 4:01:03 PM
Author: Rhino


This raises the question: First round of elimination for what? Ideal cuts? Please clarify.

I''ve done so multiple times already.....and in English, too....but ok. To eliminate diamonds with number relationships that suggest the diamond is likely to be a POOR performer. NOT to eliminate diamonds to the point where the only remaining diamonds will fit into AGS0 or GIAIdeal criteria.

Got a newsflash for ya.....some people are fine with AGS1 stones. Some like AGS2. While they aren''t AGS0, they still outperform a damn huge percentage of all available stones in the marketplace, right?

GET OFF the "ideal" terminology. That''s your problem. You keep wanting everyone else to conform to wanting the "creme de la creme"......not everyone wants that, and not everyone needs that. You keep wanting to limit discussion to ONLY AGS0 or GIA-Ideal possibilities.


Date: 11/10/2005 4:01:03 PM
Author: Rhino


Date: 11/9/2005 4:32:18 PM
Author: aljdewey

If you put one drop of red food coloring into an 4-oz glass of water, the color will change significantly....enough for me to notice. If you put one drop of red food coloring into *Lake Michigan*, there IS a measureable, infinitessimal alteration, but not one I can notice or appreciate. There is a difference between a ''measureable difference'' and an *appreciable difference*.

There''s been a lot of discussion recently about stones that score below 1 and how performance in such stones may not perform as well. HOW MUCH less well? Measureable or appreciable? If the difference means I''ll see 20% less light return in a majority of lighting conditions, that would potentially be meaningful to me....and likely appreciable to my eye.

If the difference means that I''ll only see 86.66667676767% light return instead of 86.66667676770% light return, should that matter? I don''t think so.
Good analogy and good point. Answer: Enough of a difference that the 2 most conservative labs don''t consider many of these under HCA <2 combinations to be ideal. That''s enough for most consumers to know.

I will reiterate what I said in my last post. The HCA is not a tool for determining Ideal cuts.
You are arguing a MOOT point. NO ONE has said diamonds that score under 2 on the HCA will conform to current day AGS0 or GIAIdeal standards. Why, WHY, WHY do you keep arguing a point that NO ONE is contesting? Neither did anyone say that the HCA is a tool for determining ideal cuts *according to AGS0 or GIAIdeal* parameters. That doesn''t negate its usefulness FOR ITS STATED INTENDED PURPOSE......"to eliminate known poor performers". What remains after that elimination may include both stones of exceptional cut and just above average cut.......but they are NOT "known poor performers". Capice?

Put another way.......a butter knife will never be called "the absolute sharpest instrument created by man", and it will never be able to cut a steel pipe in half. That doesn''t mean it won''t be useful FOR ITS INTENDED PURPOSE......to spread butter.




Date: 11/10/2005 4:01:03 PM
Author: Rhino

Good analogy and good point. Answer: Enough of a difference that the 2 most conservative labs don''t consider many of these under HCA <2 combinations to be ideal. That''s enough for most consumers to know.
No, it''s not enough for consumers to know. The big piece you''re missing here is what the CONSUMER can perceive as a difference.

Rich Sherwood made a VERY sage statement a few months back: "What is true "by definition" is not necessarily observable "in practice". It makes no difference to a person that a bullet drops six inches at a thousand yards when it has been fired at him from six feet. The nuance of the physics escapes him."

Look, I''m sure AGS and GIA can readily spot the nuances between a VS1 and a VS2......but *I* can''t, and most Joe Average Consumers can''t. I''m sure they can readily appreciate minute differences in light performance......but *I* can''t, and most Joe Average Consumers can''t. People at labs spend YEARS looking at thousands of stones.......they are experts. OF COURSE they are more likely to see infinitessimal differences. But that DOESN''T mean AVERAGE consumers will see them.

I just spent FIVE HOURS at Whiteflash last month; so did Mara. Faced with a wide array of stones, *we* couldn''t tell which stones were H&A and which were just shy of it. We couldn''t tell which stones were shallow pavilion angles and which weren''t. We couldn''t tell which stones had crowns over 35 and which didn''t. We couldn''t even ascertain with certainty which stones were which colors when all lined up in the tray.

Now, it''s possible that Brian, you, Garry, Dave, every member of AGS and every member of GIA could appreciate *some* minute performance differences.......but most consumers won''t be able to see such subtle differences.




Date: 11/10/2005 4:01:03 PM
Author: Rhino


This is AGS and GIA''s opinion so if you want to argue you can take it up with them.
I''m not arguing with their opinions; I''m saying that their opinions don''t dictate how much distinction a CUSTOMER''S eyes WILL see. It only dictates what the LAB sees.

The labs'' opinions is important because it narrows down what *pricing* is appropriate diamonds based on how close they come to the labs'' definitions of PERFECTION.
The CUSTOMER''S opinion is the one that determines how HE sees a diamond perform.

Thus, the labs'' opinion that my stone is an SI2 is meaningful because of its effect on the pricing of my stone. However, the fact that the lab designated my stone SI2 doesn''t mean it will look different to ME than an SI1 or a VS1......and it doesn''t. They can appreciate the difference, but I can''t.

I just don''t know how to explain this any clearer.
 

pricescope

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Date: 11/10/2005 4:01:03 PM
Author: Rhino
Ok... sticking to the informational content of this thread. Alj, please do not take my questions/comments on the information personally. They are not directed at *you* but at the information presented.

What I see happening on this forum to my dismay (and moreso to Leo''s) is that the HCA is being presented as a tool to identify beautiful diamonds. ...
emsmileo.gif
Leo doesn''t follow ... presented by who? what''s the buzz?

ALL the tools and grading systems avalailable today are not perfect. we have to deal with it.
 

aljdewey

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Date: 11/10/2005 6:06:23 PM
Author: Rhino

'A diamond scoring under a 2.0 on the HCA is ideal so there no need to worry about any other details'. (these may not have been the exact words but the message was identical, even using the word 'ideal').
Oh, most assuredly those aren't the exact words, NOR was the message identical. Not by a LONG-shot. Of course, if someone hadn't requested the removal of that thread
20.gif
, we'd be able to go back and prove that.....but alas, it is gone (but not forgotten).

First, it is important to stage the context. The person in question was confused by information overload and was FRUSTRATED. Belle's response said (not verbatim): "If you're looking to simplify it, just stick to considering stones that score under 2.0 and they'll be ideal." NOT "they'll achieve an AGS0 or GIA Ideal status". Just that they will be ideal....as in generic term ideal----SMALL letter I, not Capital letter I.

It would be like me telling you to get a band-aid. Band-aid in that context doesn't mean "Band-Aid" brand; it means any adhesive bandage GENERICALLY REFERRED TO AS A BANDAID.

Belle never asserted that as long as he stuck to less than 2.0, he would end up with an AGS0 or GIAIdeal stone. Just an "ideal" one....as in "SWEET".





Date: 11/10/2005 6:06:23 PM
Author: Rhino

In my postings however you do not see me stressing anyone's need for it or instilling fear purposely for the sake of instilling fear itself. Yes I realize that it does but let me make it clear that this is not my motives and intent here.

I don't believe you do it for the sake of instiling fear itself. I believe you do it because you want to create a problem that only *you* have the solution for, and that opinion hasn't changed.

Further, by your own admission, you realize that your delivery DOES have that effect, and yet you do nothing to mitigate it. If you know people become confused and hopeless and FEARFUL by your delivery, and you do nothing to change it, doing nothing to change it is no better than intending it in first place.
 

aljdewey

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Date: 11/10/2005 8:18:33 PM
Author: Pricescope


ALL the tools and grading systems avalailable today are not perfect. we have to deal with it.

A rousing AMEN. And no ONE tool is the be-all, end-all.
1.gif
 

Kaleigh

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Are we done now?? I need some Advil or Ibuprofen. Just kidding, but does make a point that no tools are perfect and we will have to live with that as Leonid just articulated.
 

pricescope

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And what Irina got out of all Rhino''s dissertations is that for being sure a stone is Excellent by GIA or AGS0 one needs just that - a report from a lab.

Oops, other toys go where HCA goes...
 

aljdewey

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Date: 11/10/2005 8:53:15 PM
Author: Pricescope

And what Irina got out of all Rhino''s dissertations is that for being sure a stone is Excellent by GIA or AGS0 one needs just that - a report from a lab.

Hahahaha - that''s BEAUTIFUL. Irina, hats off for coming up with the most simple answer of all.

Can you please forward it to poor Big Toque?
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If he hasn''t run into the night screaming, never to return?
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aljdewey

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Date: 11/10/2005 4:01:03 PM
Author: Rhino





Date: 11/9/2005 4:32:18 PM
Author: aljdewey

If you put one drop of red food coloring into an 4-oz glass of water, the color will change significantly....enough for me to notice. If you put one drop of red food coloring into *Lake Michigan*, there IS a measureable, infinitessimal alteration, but not one I can notice or appreciate. There is a difference between a 'measureable difference' and an *appreciable difference*.

There's been a lot of discussion recently about stones that score below 1 and how performance in such stones may not perform as well. HOW MUCH less well? Measureable or appreciable? If the difference means I'll see 20% less light return in a majority of lighting conditions, that would potentially be meaningful to me....and likely appreciable to my eye.

If the difference means that I'll only see 86.66667676767% light return instead of 86.66667676770% light return, should that matter? I don't think so.
Good analogy and good point. Answer: Enough of a difference that the 2 most conservative labs don't consider many of these under HCA <2 combinations to be ideal.

If a consumer is coming to these boards to try to find what the most conservative labs consider to be the best looking diamonds they will not find it by going to the HCA. As a matter of fact the better the HCA score the greater the possibilities the diamond is going to be a dud and a non ideal.
Let's look at some DATA.

I just did a "Search by Cut quality Search" using the following criteria: .5 to 2.5 ct., F-H color; VS1-SI2; scores 2.0 or less. Results returned 254 diamonds.

Of those 254, 50 of them scored 0.4 through 0.9 on the HCA.

Of those 50, 31 had older or no grading reports. That left 19 stones......all of which scored 0.4-0.9 and all of which were graded under NEW AGS0 system.

15 of the 19 diamonds STILL made AGS0 grading! I'd suggest the "duds" aren't as widespread as previously suggested.
1.gif


Based on this......let's just agree that we aren't going to agree. We aren't. I believe it has some value for its intended use, and you don't. You make your recommendations as you see fit, and I'll provide my consumer opinion as I see fit. This argument has become circular, for sure, and I've lost interest.

 

Garry H (Cut Nut)

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Date: 11/10/2005 9:19:13 PM
Author: aljdewey

Let''s look at some DATA.

I just did a ''Search by Cut quality Search'' using the following criteria: .5 to 2.5 ct., F-H color; VS1-SI2; scores 2.0 or less. Results returned 254 diamonds.

Of those 254, 50 of them scored 0.4 through 0.9 on the HCA.

Of those 50, 31 had older or no grading reports. That left 19 stones......all of which scored 0.4-0.9 and all of which were graded under NEW AGS0 system.

15 of the 19 diamonds STILL made AGS0 grading! I''d suggest the ''duds'' aren''t as widespread as previously suggested.
1.gif


Based on this......let''s just agree that we aren''t going to agree. We aren''t. I believe it has some value for its intended use, and you don''t. You make your recommendations as you see fit, and I''ll provide my consumer opinion as I see fit. This argument has become circular, for sure, and I''ve lost interest.
Thanks for doing that reseach Aljd.

Now if we can have my thread back.
People were asking about how to use HCA.
So yet again I post this chart for some sensible comment.

Please give up on your debate Aljd and Rhino.
It is dead.

If anyone wants to make comments on the obvious need for a change in wording on the HCA results than please feel free to make postive suggestions. For example - should this image go up with a simple directive?
Is this chart useful? Does anyone (other than GIA) challenge the information that is included on it?

Has anyone been able to find the 25 dergee crown diamond that Brad and Jan posted that proves the MSU, HCA, GIA, AGS proven relationship between crown and pavilion angles?

How to use HCA2.jpg
 

strmrdr

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ok Garry,

Ill get back to what you want to talk about.

Whose opinion do those shapes represent?
Yours alone or others?

Can you explain why you put the cutoffs where you did?

not sure how to word this one:
Can such shapes actually reflect the best ranges?
for example the ags0 range is a jagged box on the chart they seem to have found some areas that are close together on the chart that didn''t meet their standards.
 

Garry H (Cut Nut)

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Date: 11/10/2005 11:33:11 PM
Author: strmrdr
ok Garry,

Ill get back to what you want to talk about.thanks
36.gif


Whose opinion do those shapes represent?
Yours alone or others? mine alone

Can you explain why you put the cutoffs where you did? I used an '0' text character in Adobe Fonts. Rotated it and stretched it out - to about where I thought we would cover a good effective range.

not sure how to word this one:
Can such shapes actually reflect the best ranges? The AGS jagged boxes represent their steps of studied proportions with no averaging. Sergey ahs suggested the gaps and spaces etc indicate errors in logic. I think ovals are better representations of what happens in nature.
for example the ags0 range is a jagged box on the chart they seem to have found some areas that are close together on the chart that didn't meet their standards.
I have uploaded the earliest published work from MSU (Sergey and Yuri 1999?) - it seems to support the oval idea.

MSUQandTSmall.jpg
 

belle

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Date: 11/10/2005 10:47:07 PM
Author: Garry H (Cut Nut)

If anyone wants to make comments on the obvious need for a change in wording on the HCA results than please feel free to make postive suggestions. For example - should this image go up with a simple directive?
Is this chart useful? Does anyone (other than GIA) challenge the information that is included on it?

Has anyone been able to find the 25 dergee crown diamond that Brad and Jan posted that proves the MSU, HCA, GIA, AGS proven relationship between crown and pavilion angles?
no, no directives needed. it is very self explanatory.
well, except for the ''younger people'' and ''older people'' descriptors
11.gif


if brad/jan indeed posted this information on ps, it is no longer available.
 

Garry H (Cut Nut)

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I should add that the HCA chart includes a weighting for spread. i.e. diamonds in the lower left of the chart get less penalty, so HCA for pure optical performance, without the spread, an HCA chart has the red zone up a bit higher.

This is somewhat similar to a discussion we are having elsewhere about spread
34.gif
.

I decided to include spread in the HCA scores; a Tolkowsky stone gets a HCA 0.5 penalty.

You could argue that I should set Tolkowsky at 0.0 for spread - and there should be no benefit for bigger spreads.

If anyone wants to debate that with me I am happy to consider opinions.
It means that HCA would accept some stones with steeper deeper crown pavilion angles.
e.g HCA for C 35.1 P41 would be 2, as compared to currently HCA 2 = C34.9 P41 currently.
 

Garry H (Cut Nut)

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Date: 11/10/2005 11:56:10 PM
Author: belle


Date: 11/10/2005 10:47:07 PM
Author: Garry H (Cut Nut)

If anyone wants to make comments on the obvious need for a change in wording on the HCA results than please feel free to make postive suggestions. For example - should this image go up with a simple directive?
Is this chart useful? Does anyone (other than GIA) challenge the information that is included on it?

Has anyone been able to find the 25 dergee crown diamond that Brad and Jan posted that proves the MSU, HCA, GIA, AGS proven relationship between crown and pavilion angles?
no, no directives needed. it is very self explanatory. I mean this text that appears on the search page Belle - I copied it below:
well, except for the 'younger people' and 'older people' descriptors
11.gif


if brad/jan indeed posted this information on ps, it is no longer available. They posted oit on DT about 2 years back. I referred to it before with this graphic
This is the text from the HCA page that comes up under the results:

Even though HCA grades cut more effectively than systems like the AGS, it does not yet factor in symmetry and minor facets. Having found a diamond that scores well, you should employ an expert appraiser to examine the stone. If you decide not to, then at least compare the diamond to others and/or view it through an ideal-scope.

A score below 2 (Excellent) means you have eliminated known poor performers (more than 95% of all diamonds). Your own personal preference may be for a diamond with an HCA score of 1.5 more rather than one with a lower score of say 0.5.

Many diamonds with excellent scores may not be traditional 'ideal cuts' but we believe their value will rise once the GIA establishes its cut standard.
This system is being continually fine-tuned and results may change without notice.


Garry Holloway FGAA DDT
The red area on this chart represents the lowest HCA scores.

Stones near the center of the red region, those with the lowest scores, are often the least affected by small symmetry variations.

A shallower stone, on the lower part of the chart, will look darker when viewed from close up, they are not for everyone. Shallow stones have the advantage of a bigger spread. They are better suited for use as pendants and earring stones where they are not usually viewed from very close proximity (a close observers head obstructs light sources that would otherwise be returned).

Deeper proportioned stones, near the upper part of the red area, have more leakage. Leakage means reduced light return. A limited amount of reduced light return can contribute to a diamonds contrast. Diamonds with a large area of partial leakage table, seen as a pale pink area with an Ideal-Scope, are best set in open backed rings so light can get in the bottom or pavilion of the diamond. It is possible for light entering the pavilion to leak back out the top as firey dispersed colored flashes. Deeper diamonds that have perfect or hearts and arrows grade symmetry, with scores around 2, will often perform far better than diamonds of lesser symmetry.



Jans BIC2.jpg
 

belle

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are you saying you''re not considering changing the older/younger people rings verbage?
39.gif


what about the pendant/earring stone disclaimer?
 

Garry H (Cut Nut)

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Go back and read the (now) blue writting Belle - that is what is on the page at present.

What do
35.gif
you
35.gif
thik should be written there?
What would be best as warnings to newbies and good ways to use HCA.
 

valeria101

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Date: 11/11/2005 12:10:01 AM
Author: Garry H (Cut Nut)



Even though HCA grades cut based on the same principles as the AGS system more effectively than systems like the AGS, it does not yet factor in symmetry and minor facets. These details are considered by more advanced cut grading systems to various degrees, but never instead on the important parameters taken into account by the HCA. The grading method behind the HCA is compatible with the majority of diamond cut grading tools on the market today. However, the HCA has the advantage of giving valuable advice about the potential of a diamond based on very scarce information. This makes the Cut Adviser useful for making a choice when comparable cut quality grades are available for all (or any) of the diamonds considered.


The HCA gives an educated guess of diamond cut quality. It cannot guess buyers' taste and does not void any other expert opinion based on more information (aside table, depth, crown and pavilion angles). Having found a diamond that scores well, you should employ an expert appraiser to examine the stone. If you decide not to, then at least compare the diamond to others and/or view it through an ideal-scope.

A score below 2 (Excellent) means you have eliminated known poor performers (more than 95% of all diamonds). Your own personal preference may be for a diamond with an HCA score of 1.5 more rather than one with a lower score of say 0.5.

Many diamonds with excellent scores may not be traditional 'ideal cuts' but we believe their value will rise once the GIA establishes its cut standard.
This system is being continually fine-tuned and results may change without notice.




Garry Holloway FGAA DDT
The red area on this chart represents the lowest HCA scores.

Stones near the center of the red region, those with the lowest scores, are often the least affected by small symmetry variations.

A shallower stone, on the lower part of the chart, will look darker when viewed from close up, they are not for everyone. Shallow stones have the advantage of a bigger spread. They are better suited for use as pendants and earring stones where they are not usually viewed from very close proximity (a close observers head obstructs light sources that would otherwise be returned).

Deeper proportioned stones, near the upper part of the red area, have more leakage. Leakage means reduced light return. A limited amount of reduced light return can contribute to a diamonds contrast. Diamonds with a large area of partial leakage table, seen as a pale pink area with an Ideal-Scope, are best set in open backed rings so light can get in the bottom or pavilion of the diamond. It is possible for light entering the pavilion to leak back out the top as fiery dispersed colored flashes. Deeper diamonds that have perfect or hearts and arrows grade symmetry, with scores around 2, will often perform far better than diamonds of lesser symmetry.

The color markings say: gray is out, orange in.

... you can probably tell I haven't written a disclaimer until now. I hope the idea is pretty clear as is, if anything I wish I had some much shorter and clearer wording for it.
 

Dancing Fire

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Date: 11/10/2005 9:19:13 PM
Author: aljdewey

Date: 11/9/2005 4:32:18 PM
Author: aljdewey
Let''s look at some DATA.

I just did a ''Search by Cut quality Search'' using the following criteria: .5 to 2.5 ct., F-H color; VS1-SI2; scores 2.0 or less. Results returned 254 diamonds.

Of those 254, 50 of them scored 0.4 through 0.9 on the HCA.

Of those 50, 31 had older or no grading reports. That left 19 stones......all of which scored 0.4-0.9 and all of which were graded under NEW AGS0 system.

15 of the 19 diamonds STILL made AGS0 grading! I''d suggest the ''duds'' aren''t as widespread as previously suggested.
1.gif


Based on this......let''s just agree that we aren''t going to agree. We aren''t. I believe it has some value for its intended use, and you don''t. You make your recommendations as you see fit, and I''ll provide my consumer opinion as I see fit. This argument has become circular, for sure, and I''ve lost interest.
Alj
are you crying UNCLE?
31.gif
this would be the second time in PS history
9.gif
11.gif
 

KristyDarling

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It's classic PS threads like this one that make my head spin. Good golly!!!!
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All I know is, I love my shiny new sparkler even though it has an HCA score of 2.8. It is still pretty darned blinding.
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(and interestingly, my independent appraiser Nancy Stacy actually picked mine over another AGS0 that had a 1.1 HCA. Said it had better light performance. Go figure! Aahhh, the mysteries of diamond.)
 

Dancing Fire

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Garry
what do you mean by OLDER people ring?
33.gif
how old do you have to be?
34.gif
 

Paul-Antwerp

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Date: 11/11/2005 2:31:07 AM
Author: Dancing Fire
Garry
what do you mean by OLDER people ring?
33.gif
how old do you have to be?
34.gif
Probably, mid-life-crisis can be described as the point in time, when your wife (getting older) does not like the proportions of her stone anymore, and it is high time to find a younger girlfriend.

Could this be it, Garry?
 

Dancing Fire

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Date: 11/11/2005 3:21:39 AM
Author: Paul-Antwerp




Date: 11/11/2005 2:31:07 AM
Author: Dancing Fire
Garry
what do you mean by OLDER people ring?
33.gif
how old do you have to be?
34.gif
Probably, mid-life-crisis can be described as the point in time, when your wife (getting older) does not like the proportions of her stone anymore, and it is high time to find a younger girlfriend.

Could this be it, Garry?
Paul
the next time when you do a "custom cut" for me,i'll make sure to order the "YOUNG MISTRESS CUT" by Infinity.
2.gif
 

Regular Guy

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I''ll just share a few points:


Date: 11/10/2005 10:47:07 PM
Author: Garry H (Cut Nut)

Now if we can have my thread back.
So, point #1:

Actually, as you pointed out a bit earlier:

"Exactly Alj, and this is why i migrated the discussion to this old Ira thread."

Your idea, my thread. OK.

And Garry, while you''re clarifying nits in language on the HCA tool, you might turn your attention to the first post in this thread, if you care to want to clarify any further than you have, if you can, those 3 views of the HCA, examples of which we can attribute each to yourself, as well. Or you can forgetaboudit. Frankly, even beyond your clarifying today''s language in the HCA tool, you have bigger fish to fry for tomorrow; see below.

Point/Question #2


Date: 11/10/2005 10:47:07 PM
Author: Garry H (Cut Nut)
Is this chart useful? Does anyone (other than GIA) challenge the information that is included on it?
Can you say more about how HCA and GIA are counter to each other?

Earlier, based on comments from Paul and others, I was led to believe the new GIA "best" may represent 50% of what they get their hands on. More recently, particularly with Rhino''s comments, there is a suggestion their system has more teeth. Garry, how do you see their standards different than yours?

Suggestion #3

HCA''s helpfulness lies in it''s simplicity. Making demands for the reader to Figure out with the new annotated chart where a diamond aligns with age and such does not help a lot, overall, so I''d say keep at as a backup resource.

Thought #4

I like Ana''s attempt at revisionist language, but let''s look more closely at the detail in the revised first paragraph:

"Even though HCA grades cut based on the same principles as the AGS system more effectively than systems like the AGS, it does not yet factor in symmetry and minor facets. These details are considered by more advanced cut grading systems to various degrees, but never instead on the important parameters taken into account by the HCA. The grading method behind the HCA is compatible with the majority of diamond cut grading tools on the market today. However, the HCA has the advantage of giving valuable advice about the potential of a diamond based on very scarce information. This makes the Cut Adviser useful for making a choice when comparable cut quality grades are available for all (or any) of the diamonds considered."

Ana''s text in yellow above does a good acknowledgement to GIA''s cut grading system just around the corner, and the second set of highlighted text is in agreement that, for those diamonds with no certificate, and with just table and depth, pavilion, and crown angle info, it will help a great deal. What will helpful to put into perspective, in some consideration of question #3 and observation #4, is the degree to which HCA remains a more descriptively predictive tool than the new GIA, particularly in consideration of the additional minor facet variables GIA''s new system ostensibly will begin to engage as well.
 

strmrdr

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Garry,
I think your proposed change in wording more accuratly reflects the visual performance of the diamonds themselves and is a good step.

As for the chart it looks good to me there are some areas where some combos are in slightly different places than Id put them but I dont know if its enough to matter.

Its a lot to think about because there is a ton of information in just 2 stretched 0''s on a chart.
 

valeria101

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Date: 11/11/2005 6:49:13 AM
Author: Regular Guy
I''ll just share a few points:

...the degree to which HCA remains a more descriptively predictive tool than the new GIA, particularly in consideration of the additional minor facet variables GIA''s new system ostensibly will begin to engage as well.

Thanks !
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I am afraid I don''t understand what a ''descriptive prediction'' is. If the core of the question is "How much does the HCA miss for not including minor facets''", THAT I would love to know myself.

More data is probably a good thing, but ... it doesn''t make things more straight forward this time. Perhaps GIA''s system had to be innovative and restrict bootleg use etc. but let''s forget these guys need a certain type of channel to promote research findings. Probably no cut grading system is spared the same communication bias - all better reason to question what does what.

Not that this thread needs more digression.
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There could easily be another if anyone finds the question useful.
 

aljdewey

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Date: 11/11/2005 2:22:34 AM
Author: valeria101


Date: 11/11/2005 12:10:01 AM
Author: Garry H (Cut Nut)





Even though HCA grades cut based on the same principles as the AGS system more effectively than systems like the AGS, it does not yet factor in symmetry and minor facets. These details are considered by more advanced cut grading systems to various degrees, but never instead on the important parameters taken into account by the HCA. The grading method behind the HCA is compatible with the majority of diamond cut grading tools on the market today. However, the HCA has the advantage of giving valuable advice about the potential of a diamond based on very scarce information. This makes the Cut Adviser useful for making a choice when comparable cut quality grades are available for all (or any) of the diamonds considered.


The HCA gives an educated guess of diamond cut quality. It cannot guess buyers' taste and does not void any other expert opinion based on more information (aside table, depth, crown and pavilion angles). Having found a diamond that scores well, you should employ an expert appraiser to examine the
The color markings say: gray is out, orange in.

... you can probably tell I haven't written a disclaimer until now. I hope the idea is pretty clear as is, if anything I wish I had some much shorter and clearer wording for it.

I'd change to "The HCA gives an educated opinion of expected diamond cut quality. It cannot predict buyers' taste and
 

JohnQuixote

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I've been away from the internet for a few days, but took some time to look through this thread this morning.

I believe the point you frequently make about rejection over selection should be up-front, and some of the tweaks suggested by others are nice sauce for the goose, but not a lot has to change. Ultimately it is your creation, so say what you want to say, on your terms.

For what it's worth, here's my 2 cents (also incorporating some coinage from others) on the first part, as long as we're tossing pennies into the HCA wishing well.
1.gif








IMPORTANT NOTES: The HCA is best used to identify and reject poor performers, not for final selection among excellent diamonds. A score below 2 (Excellent) means you have eliminated known poor performers (more than 95% of all diamonds). Scores below 2 may be treated equally in overall terms. Your own personal preference may be for a diamond with an HCA score of 1.5 rather than one with a lower score of say 0.5.

The HCA score is an educated opinion on diamond cut quality. It cannot predict buyers' taste, and does not void any other expert opinion based on information beyond depth, table, crown and pavilion angles. Even though HCA grades cut effectively it does not yet factor in symmetry and minor facets. These details are considered in other systems to varying degrees, but never in place of the prime measurements incorporated into the HCA. The HCA has the advantage of giving valuable advice about a diamond’s potential based on only 5 measurements. Having found a diamond that scores well, you should employ an expert appraiser to examine the stone. If not, then at least compare the diamond to others and/or view it through an ideal-scope.

Many diamonds with excellent scores may not be traditional 'ideal cuts' but we believe their value will rise once the GIA establishes its cut standard.

This system is being continually fine-tuned and results may change without notice.

 

strmrdr

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"A shallower stone, on the lower part of the chart, will look darker when viewed from close up, they are not for everyone. Shallow stones have the advantage of a bigger spread. They are better suited for use as pendants and earring stones where they are not usually viewed from very close proximity (a close observers head obstructs light sources that would otherwise be returned)."

thats the part that needs to be added and ill be happy.
not all stones under 2hca are well suited for all uses, they may be the best for their niche but not the best for some uses.
 

belle

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Nov 19, 2004
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leaning heavily on what is already out there, here is my draft:



IMPORTANT NOTES: The HCA is best used to identify and reject poor performers based on relative proportion combinations. it is not intended for use in final selection among excellent diamonds. A score below 2 (Excellent) means you have eliminated known poor performers and therefore more than 95% of all diamonds. Scores below 2 may be treated equally in overall terms and lower scores should not be considered better. Your own personal preference may be for a diamond with an HCA score of 1.5 rather than one with a lower score of say 0.5.

The HCA score is an educated opinion on diamond cut quality. It cannot predict buyers'' taste, and does not void any other expert opinion based on information beyond depth, table, crown and pavilion angles. Even though HCA grades cut effectively it does not yet factor in symmetry and minor facets. These details are considered in other systems to varying degrees, but never in place of the prime measurements incorporated into the HCA. The HCA has the advantage of giving valuable advice about a diamond’s potential based on only 5 measurements. Having found a diamond that scores well, you should consider the advice of an expert to examine the stone. If not, then at least compare the diamond to others and/or view it through an ideal-scope.


Many diamonds with excellent scores may not be traditional ''ideal cuts'' but we believe their value will rise once the GIA establishes its cut standard.



This system is being continually fine-tuned and results may change without notice.
 

strmrdr

Super_Ideal_Rock
Joined
Nov 1, 2003
Messages
23,295
IMPORTANT NOTES: The HCA is best used to identify and reject poor performers based on relative proportion combinations. it is not intended for use in final selection among excellent diamonds. A score below 2 (Excellent) means you have eliminated known poor performers and therefore more than 95% of all diamonds.
The HCA score is an educated opinion on diamond cut quality. It cannot predict buyers'' taste, and does not void any other expert opinion based on information beyond depth, table, crown and pavilion angles. Even though HCA grades cut effectively it does not yet factor in symmetry and minor facets. These details are considered in other systems to varying degrees, but never in place of the prime measurements incorporated into the HCA. The HCA has the advantage of giving valuable advice about a diamond’s potential based on only 5 measurements. Having found a diamond that scores well, you should consider the advice of an expert to examine the stone. If not, then at least compare the diamond to others and/or view it through an ideal-scope.

Many diamonds with excellent scores may not be traditional ''ideal cuts''.
Some diamonds that score in the lower ranges may be better suited for pendants and earrings. Some cut grades do not consider these to be ideal cuts because there are better combos available for all around use. They can however be the best combos for their intended use which is why they are included in the top 5%.

This system is being continually fine-tuned and results may change without notice
 
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