Seduced by the HCA

[JHChin]

I''d like begin by thanking the PS community! Everyone here seems extra nice and extra helpful. It''s great to have this forum as an available resource for making the best possible purchasing decisions.

So for the topic at hand...

I''ve heard a lot of people say, "Use the HCA as an elimination tool, not a selection tool." I''d to hear some insight that explains this axiom a little bit further. Because the truth is... It''s really easy to get seduced by the HCA! I mean, you plug in the 4 simple metrics (5 if you have a culet) and BAM you get a score that grades your diamond! How easy is that?

Sure, that doesn''t mean I''ve left out the 4C''s, but beyond the 4C''s and the HCA, is there anything meaningful left taking into consideration?

So lets say you take two diamonds that have the same 4C''s (as per GIA reports):

Carot: 1.5ct
Color: G
Clarity: VS1
Cut: Excellent

Then the other more obvious metrics are also the same:
Finish: Excellent
Symmetry: Excellent
Fluorescence: None
Culet: None

Now diamond A gets an HCA score of 1.5 and diamond B gets an HCA score of 1.7. With all the other previously mentioned metrics being equal, why would you not take diamond A every time? Is there something else I''m missing? I''ve now selected A instead of B because of the HCA -- thus defying our favorite axiom!

Sure ultimately, I''d want to see both diamond A and B next to each other for the sake of comparison... What really beats that? But pragmatically speaking, in the age of Internet diamond purchasing, are we really at the liberty of being able to see both diamonds next to each other?

As one last parting question... I''d also like to hear some feedback on what people think of the differences between H & G colors, and VS1 & VS2 clarity.

Thanks in advance!
-Jordan

 

[Lorelei]

Date: 7/7/2009 3:20:01 PM
Author:JHChin
I'd like begin by thanking the PS community! Everyone here seems extra nice and extra helpful. It's great to have this forum as an available resource for making the best possible purchasing decisions.

So for the topic at hand...

I've heard a lot of people say, 'Use the HCA as an elimination tool, not a selection tool.' I'd to hear some insight that explains this axiom a little bit further. Because the truth is... It's really easy to get seduced by the HCA! I mean, you plug in the 4 simple metrics (5 if you have a culet) and BAM you get a score that grades your diamond! How easy is that?

Sure, that doesn't mean I've left out the 4C's, but beyond the 4C's and the HCA, is there anything meaningful left taking into consideration?

So lets say you take two diamonds that have the same 4C's (as per GIA reports):

Carot: 1.5ct
Color: G
Clarity: VS1
Cut: Excellent

Then the other more obvious metrics are also the same:
Finish: Excellent
Symmetry: Excellent
Fluorescence: None
Culet: None

Now diamond A gets an HCA score of 1.5 and diamond B gets an HCA score of 1.7. With all the other previously mentioned metrics being equal, why would you not take diamond A every time? Is there something else I'm missing? I've now selected A instead of B because of the HCA -- thus defying our favorite axiom!

Sure ultimately, I'd want to see both diamond A and B next to each other for the sake of comparison... What really beats that? But pragmatically speaking, in the age of Internet diamond purchasing, are we really at the liberty of being able to see both diamonds next to each other?

As one last parting question... I'd also like to hear some feedback on what people think of the differences between H & G colors, and VS1 & VS2 clarity.

Thanks in advance!
-Jordan

Because a lower score isn't better! The aim is to score below 2 in most cases, then such diamonds are considered worth further evalutation. That is when images such as ASET and Idealscope come into play as far as " seeing and comparing" as the next stage. The HCA is also working on limited info and it cannot physically see the stone.

H &G colours...I can't tell the difference between these if GIA or AGS graded, and VS clarities, if eyeclean and in the majority of cases these will be, I can't tell a difference with the naked eye either, even some eyeclean SI clarities come to that.

 

[jet2ks]

What the HCA does is give a basic outline of the diamond based on the averages of just a few of the 57 facets. How much variation there is in the numbers that are being averaged can have a large impact in diamond performance, as can the "minor" facets that aren't taken into consideration by the HCA.

What this tool does is increase your odds, not give a definite answer. The vast majority of stones scoring under 2 are going to be good performers. Some stones scoring 2-3 are also going to be good performers, just not as high a percentage in relation to the whole. There will even be some diamonds that would score over 3 that will be good in person, but it is a much lower percentage yet. What the HCA does is allow you to eliminate groups of diamonds where your odds of finding a good one are lower and leaves you with a group (those scoring under 2) that will have high odds of finding a good stone. Like any tool, the HCA can be misused if applied in the wrong way.

Maybe a basketball analogy. You have to place a wager on an NBA player making a lay-up, a three pointer or a full court desperation type shot. You will win the same exact amount of money no matter what shot you wager on, so which do you want him to shoot? Whether the lay up is from 1 1/2 ft or 2 ft won't really change the odds. (Sorry, there are no slam dunks in diamonds

)

 

[Regular Guy]

JH I might have (and did!) say the same thing 2 - 4 years ago.

HCA is linearistic, but not practically linear. That is...that is sort of linear is sort of obvious.

As you get closer to 0...the interpretation gets complicated at least...and therefore, both observations, and Garry''s formula yield...when it''s below 2, results that are more challenging to interpret. That goes to just the philosophical underpinnings.

Beyond that...there''s the question of measurement precision. Even if HCA is singing, the diamond''s proportions a) may not perfectly present as what''s presented and b) the minor facets, also a part of the totality, are not being accounted for, however, using the same principles, c) both AGS and GIA use the same metric concepts to describe quality, with most believing AGS''s model more, and with AGS platinum measuring those additional parts (minor facets)

Finally, there''s what''s not accounted for in cut in what the HCA is designed to measure...and likewise, with IS and ASET reflector technology, there are some qualities not presented that you might be interested in anyway. For example, although IS trumps HCA, it is not supposedly sensitive to Fire, even though fire is in the presentation of metrics included in the HCA.

Some thoughts...

 

[Rockdiamond]

There have been many cases where observiers pick a stone with an HCA score higher than 2 after comparing with stones earning scores less than 2.
Of course there have been loads of cases where observers did pick the stone with the lower HCA score.

I agree with Ira. It really depends on what you''re looking for...and there are no slam dunks here.

 

[whatmeworry]

The reason you don''t take the 1.5 every time is because of your own personal preference. Most cut grades have a scoring system. The HCA is 2 parts brightness, 1 part fire, 1 part scint. Your''s might differ, say equal parts brightness, fire, and scint. It''s hard to compare virtual diamonds side by side, but that doesn''t prevent you from looking at diamonds in person so you can find out what your preference is (not just cut but the other C''s) before you purchase on the internet.

 

[Todd Gray]

The HCA results are based on the limited input required which is based on the average measurements that appear on the lab report, the next step is to obtain a computerized proportions analysis showing the facet-by-facet structure of the diamond and the high and low measurements which are the basis for the average measurements.

The HCA is not an indicator of optical symmetry, thus it is also necessary to compare ASET, Ideal Scope, H&A images of the diamonds being compared in order to make an accurate comparison and an educated decision...

The HCA does what it is intended to do which is weed out "potential" top performers from diamonds which are likely to exhibit less light return... That''s it. I think Regular Guy did bring this up a few years back, it made for an interesting thread and debate as I recall.

 

[Regular Guy]

Date: 7/7/2009 6:01:46 PM
Author: Todd Gray


The HCA does what it is intended to do which is weed out ''potential'' top performers from diamonds which are likely to exhibit less light return... That''s it. I think Regular Guy did bring this up a few years back, it made for an interesting thread and debate as I recall.

Hi, Todd. Yes, there were many many many. Could have been this one you were thinking about. In it...

a) we do revisit some of the same core topics as JHChin, along with some other ones we haven''t heard from for a while.
b) we get a history and creation lesson on the text used to accompany the read out on the HCA
c) we see where, at least at that time, several times when I composed a post, Garry time after time confused me with Karl, aka Storm...

Fun bedtime reading...

 

[strmrdr]

Date: 7/7/2009 11:22:48 PM
Author: Regular Guy

Date: 7/7/2009 6:01:46 PM

Author: Todd Gray



The HCA does what it is intended to do which is weed out 'potential' top performers from diamonds which are likely to exhibit less light return... That's it. I think Regular Guy did bring this up a few years back, it made for an interesting thread and debate as I recall.

Hi, Todd. Yes, there were many many many. Could have been this one you were thinking about. In it...


a) we do revisit some of the same core topics as JHChin, along with some other ones we haven't heard from for a while.

b) we get a history and creation lesson on the text used to accompany the read out on the HCA

c) we see where, at least at that time, several times when I composed a post, Garry time after time confused me with Karl, aka Storm...


Fun bedtime reading...

Reading that thread makes me feel old.
We have came a long way in understanding diamond cut since that thread 4 years ago.
Some of it is outdated, some of it we understand much more.

 

[Garry H (Cut Nut)]

You have 2 diamonds to choose from
A is H Flawless
B is D VS2

Both cost exactly the same.
Which is best?

 

[oldminer]

The title of this thread alone "Seduced by the HCA" was enough to get Garry''s interest.

Since the the HCA alone does not predict optical symmetry it is quite possible that some diamonds which score low (better), would not rate as Ideal Cut under the accepted systems. However, does anyone have a physicl example of a low (better) scoring HCA diamond which actually possessed only "good" or "fair" symmetry? Would a cutter allow such a potentially fine example of cutting be cut in an adverse manner? How would such a diamond look? Would it still be a worthy contender in appearance at "good" or would it fail at "fair" to look acceptable?

What amount of optical assymetry would create a visual problem is an HCA 1.5 diamond which would cause it to look unacceptable? Any examples or guidance would be of interest.

Garry, do you have a low scoring HCA example diamond that we might use as a demo of symmetry defect still with a low HCA score?

 

[JHChin]

Date: 7/8/2009 12:11:40 AM
Author: Garry H (Cut Nut)
You have 2 diamonds to choose from

A is H Flawless

B is D VS2


Both cost exactly the same.

Which is best?

Here is my personal belief... And I might catch some flack for this... But neither one is better than the other. Here its left entirely up to personal choice. Some people want the colorless diamond and care very little for the possibility that 1 in 100 might see inclusions by the naked eye. Others might carry around a magnified glass with them and like to look at inclusions for fun -- and enjoy looking at flawless diamonds.

So as for a matter of taste, I would go with diamond B.

 

[oldminer]

Personal taste will always be a major component of diamond selection. For that the diamond industry should give thanks. If personal taste had nothing to do with the process, diamonds would be able to become a pure financial commodity. This would surely take a great deal of the magic away from diamonds as both a romantic and an important gift.

No matter how we develop tools to screen or to grade diamonds, the subjective decision of which one is the right one to purchase overrides all the screening and grading we might do. The screening and grading is highly important to forming an intelligent choice of what to buy, but it does not necessarily dictate an identical final choice for every consumer. The total of the knowledge provided adds up in a personal way for each buyer. I think this ends up being a good thing so long as the information the buyer uses is given in a fair and objective manner.

Consumers do need to be protected from less than fair advice or from biased sources. Education is the best way to give yourself the benefit of the best possible deal.

 

[Modified Brilliant]

And once upon a time....before the invention of cut grading systems....consumers actually
relied upon vision only to find their perfect diamond. Imagine that!
(And that''s why grandma''s and great-grandma''s diamond kinda looked lumpy or way too spready)
Better to use the tools available and understand their positive aspects but also their limitations.

www.metrojewelryappraisers.com

 

[Lorelei]

Date: 7/8/2009 10:38:51 AM
Author: Modified Brilliant
And once upon a time....before the invention of cut grading systems....consumers actually
relied upon vision only to find their perfect diamond. Imagine that!
(And that's why grandma's and great-grandma's diamond kinda looked lumpy or way too spready)
Better to use the tools available and understand their positive aspects but also their limitations.

www.metrojewelryappraisers.com

In other words.....

* To the tune of Greensleeves*

In days of old.....
When diamonds were sold....
Before cut grades were invented....

Consumers would buy...
Just with their eye....
And walk away contented.....

 

[oldminer]

In days of old.....
When diamonds were sold....
Before cut grades were invented....
Consumers would buy...
Just with their eye....
And walk away contented.....


True enough! There was a lot more happiness overall when there was nothing but trust, love, tradition and good vision involved.
Hard to imagine now, but I had 55 years without a cell phone interrupting my driving or daily life. I find life more hectic, more pressured and more fragmented today, but, on balance, work and living has become more "efficient" and our friends can be in touch more easily and often. We create the tools which lead us both to destruction and added creativity. In the end, we must be the ones who decide how to live our lives or even what diamonds to buy.

 

[Abril]

Once you get below 2 on the HCA, the lower the score the shallower the diamond tends to be. For example, a diamond that scores 0.6 is usually shallower than one that scores 1.9. Which one you choose depends on your personal preference, and this is where your eyes come in.

 

[John P]

Date: 7/8/2009 10:43:57 AM
Author: Lorelei

In other words.....

* To the tune of Greensleeves*

In days of old.....
When diamonds were sold....
Before cut grades were invented....

Consumers would buy...
Just with their eye....
And walk away contented.....

(and the chorus)

BUT. NOW. We have the 'net
The shopper can't see the diamond yet...
HELP! HELP! Here's the HCA
And scopes and numbers (I'm dizzy).

Sorry, but it's my favourite carol and I couldn't leave it hanging.

 

[Lorelei]

Date: 7/8/2009 11:30:04 AM
Author: John Pollard

Date: 7/8/2009 10:43:57 AM
Author: Lorelei

In other words.....

* To the tune of Greensleeves*

In days of old.....
When diamonds were sold....
Before cut grades were invented....

Consumers would buy...
Just with their eye....
And walk away contented.....

(and the chorus)

BUT. NOW. We have the ''net
The shopper can''t see the diamond yet...
HELP! HELP! Here''s the HCA
And scopes and numbers (I''m dizzy).

Sorry, but it''s my favourite carol and I couldn''t leave it hanging.

BRILLIANT!!!!!!