Wondering while looking at HCA-results

[Paul-Antwerp]

Yesterday, I saw a thread in which a consumer posted two stones with their HCA-results, and this got me wondering. Now, it has been a long time since I learned about HCA, and I might have forgotten how it is designed to give a score on fire and scintillation. So, here I am, somewhat bewildered, and maybe Garry can give some info.

Stone number 1 had the following figures:

Depth = 58.9%
Table = 56%
Crown Angle = 31.5
Pavillion Angle = 40.4
HCA Grade = 1.5 (BIC type)
EX fire, scintillation, & spread; VG light return

Stone number 2 had these figures:

Depth = 61.5%
Table = 56%
Crown Angle = 34
Pavilion Angle = 41
HCA Grade = 1.3 (Excellent – TIC)
EX light return, fire; VG scintillation, spread

I was surprised that both scored EX on Fire, although there is an enormous difference in crown angle.
At the same time, I see one stone scoring VG on scintillation, and the other EX, and I have the faintest idea what this could be based upon.

Please enlighten me.

 

[Regular Guy]

bumping in support of teesers.

 

[jayreneepea]

I''ve been curious about these HCA scores myself. What I found curious is that it was determined without seeing pics or any other information on the stones that they should be passed up on. Now, I understand that the HCA is used to weed out bad stones, but if one can tell by looking at the numbers whether a stone is worthy or not, whether or not it scored well on the HCA, why do we need the HCA?

 

[Cehrabehra]

Date: 11/7/2006 8:33:37 PM
Author: jayrenay9
I''ve been curious about these HCA scores myself. What I found curious is that it was determined without seeing pics or any other information on the stones that they should be passed up on. Now, I understand that the HCA is used to weed out bad stones, but if one can tell by looking at the numbers whether a stone is worthy or not, whether or not it scored well on the HCA, why do we need the HCA?

ease? I dunno, the more I learn about diamonds the more I thinkt he old fashioned way (eyes) is best!

 

[Regular Guy]

Probably a bad example...but if someone were to tell me you could know 41 was a factor of 2952 by doing division, I would tend to believe them. In principle, you might call the system of division something like the HCA. It doesn''t mean the answer is correct by the statement, (or, importantly, the answer obvious until you do the division) even if it is believable at the outset. Turns out in this case, it is true. Also, if the result was misstated, and 41 was really a factor of 2962, it wouldn''t necessarily make the system of division bogus...just the application wrong.

Not sure if anyone would like to challenge the substance of the principles upon which an HCA exists, or for that matter, the logic that AGS use to use, etc. Maybe they would. Interpreting the data correctly may or may not present challenges. Paul''s question seems primarily based on questioning some output, and the imputed basis for it.

 

[JulieN]

Date: 11/7/2006 8:33:37 PM
Author: jayrenay9
I''ve been curious about these HCA scores myself. What I found curious is that it was determined without seeing pics or any other information on the stones that they should be passed up on. Now, I understand that the HCA is used to weed out bad stones, but if one can tell by looking at the numbers whether a stone is worthy or not, whether or not it scored well on the HCA, why do we need the HCA?

it''s like Diamond Cut for Dummies

 

[strmrdr]

Good question Paul, Further without knowing the lgf%, star%, upper girdle angle and girdle type,, not to mention the range its pretty hard to classify fire, light return and scint.

What I use the hca for is to tell if the average crown angle might work well with the average pavilion angle and thats it.
Its a quick and dirty filter that I can further narrow down from there.
Garry has a love affair with shallow stones that I dont share so thats why I said might instead of will.
For stones in the "normal" range.. 34-34.9/40.7-40.9 and low 34s with 41, I usualy dont bother running it.
But for example if I see a 33.5/41.1 id run it through the HCA.

 

[lojack_ii]

Date: 11/7/2006 8:33:37 PM
Author: jayrenay9
I''ve been curious about these HCA scores myself. What I found curious is that it was determined without seeing pics or any other information on the stones that they should be passed up on. Now, I understand that the HCA is used to weed out bad stones, but if one can tell by looking at the numbers whether a stone is worthy or not, whether or not it scored well on the HCA, why do we need the HCA?

Personally, I think the HCA is one of the best little grading systems I have found for weeding out bad stones. Just plug in the numbers and out comes a good estimate of how that diamond will return light. It''s quick and informative.

 

[Cehrabehra]

Date: 11/7/2006 10:38:43 PM
Author: lojack_ii

Date: 11/7/2006 8:33:37 PM
Author: jayrenay9
I''ve been curious about these HCA scores myself. What I found curious is that it was determined without seeing pics or any other information on the stones that they should be passed up on. Now, I understand that the HCA is used to weed out bad stones, but if one can tell by looking at the numbers whether a stone is worthy or not, whether or not it scored well on the HCA, why do we need the HCA?

Personally, I think the HCA is one of the best little grading systems I have found for weeding out bad stones. Just plug in the numbers and out comes a good estimate of how that diamond will return light. It''s quick and informative.

I think for the majority of purchasers, that''s accurate. I think that the more you learn the more you realize that it is a tool that isn''t perfect. I bet a lot of *wonderful* stones have been passedup on because they "failed" the hca.

 

[Garry H (Cut Nut)]

Paul I am on vacation - Drena will only let me out of her sight for a few minutes at a time

The very shallow stones have a lot of extinction which allows them to show a lot of fire.

I invite all of you who have access to a varity of diamonds to test it.l

 

[Paul-Antwerp]

Date: 11/8/2006 8:58:07 PM
Author: Garry H (Cut Nut)
Paul I am on vacation - Drena will only let me out of her sight for a few minutes at a time

The very shallow stones have a lot of extinction which allows them to show a lot of fire.

I invite all of you who have access to a varity of diamonds to test it.l

So, shallow stones have excellent fire, Tolkowsky-proportions or thereabout also have excellent fire, and then, there still is the Fiery Ideal Cut, with steeper crown angle, which also has excellent fire.

This confuses me.

Live long,

 

[Garry H (Cut Nut)]

This raw data has not been changed much Paul - and it has been on display here for about 6 years.

It is not a secret.
http://diamond-cut.com.au/12_fire.htm

 

[Ellen]

Date: 11/9/2006 10:33:56 AM
Author: Paul-Antwerp

So, shallow stones have excellent fire, Tolkowsky-proportions or thereabout also have excellent fire, and then, there still is the Fiery Ideal Cut, with steeper crown angle, which also has excellent fire.

This confuses me.

Live long,

Paul, this thread sheds some (colored) light on things.

https://www.pricescope.com/community/threads/1-01-k.52723/=

 

[Regular Guy]

Date: 11/9/2006 10:33:56 AM
Author: Paul-Antwerp

So, shallow stones have excellent fire, Tolkowsky-proportions or thereabout also have excellent fire, and then, there still is the Fiery Ideal Cut, with steeper crown angle, which also has excellent fire.

This confuses me.

Paul, still confused?

 

[Paul-Antwerp]

Date: 11/11/2006 8:52:02 AM
Author: Regular Guy

Date: 11/9/2006 10:33:56 AM
Author: Paul-Antwerp

So, shallow stones have excellent fire, Tolkowsky-proportions or thereabout also have excellent fire, and then, there still is the Fiery Ideal Cut, with steeper crown angle, which also has excellent fire.

This confuses me.

Paul, still confused?

It is very clear now.

BIC (see example above) has Excellent Fire.
TIC (see example above) has Excellent Fire
FIC logically has Excellent Fire

Deduction, any IC has Excellent Fire.

Live long,

 

[lojack_ii]

Date: 11/8/2006 2:01:37 AM
Author: Cehrabehra

Date: 11/7/2006 10:38:43 PM

Author: lojack_ii

Date: 11/7/2006 8:33:37 PM

Author: jayrenay9

I''ve been curious about these HCA scores myself. What I found curious is that it was determined without seeing pics or any other information on the stones that they should be passed up on. Now, I understand that the HCA is used to weed out bad stones, but if one can tell by looking at the numbers whether a stone is worthy or not, whether or not it scored well on the HCA, why do we need the HCA?

Personally, I think the HCA is one of the best little grading systems I have found for weeding out bad stones. Just plug in the numbers and out comes a good estimate of how that diamond will return light. It''s quick and informative.

I think for the majority of purchasers, that''s accurate. I think that the more you learn the more you realize that it is a tool that isn''t perfect. I bet a lot of *wonderful* stones have been passedup on because they ''failed'' the hca.

You''re probably right, but if you can''t see the stone in person before you buy and you don''t have access to every little bit of information that is humanly possible then this is a good helpful grader. I''d rather miss some good stones than pick a possibly terrible one because I didn''t know about the effects of crown & pavilion angles, etc.