Stone with HCA score under 1.0 tends to have very poor performance. Is this true?!

[oceanbeach]

I was told by a vendor that stones that score under 1.0 (HCA) tend to have very poor real life performance. Is this true?! I''m currently considering a stone which has HCA score of 0.6, and now I''m concerned about the low HCA score... The respected vendor who has the stone tells me that it is a beautiful stone, and the Ideal Scope pic looks good too. Should I be concerned about the low score?

 

[strmrdr]

they can sometimes be a problem but a good vendor can weed out the problem stones.

What are the crown and pavilion angles?

 

[oceanbeach]

Date: 8/7/2006 10:45:13 PM
Author: strmrdr
they can sometimes be a problem but a good vendor can weed out the problem stones.


What are the crown and pavilion angles?

Crown angle is 34.3, and pavilion angle is 40.6. thanks!

 

[strmrdr]

Date: 8/7/2006 10:46:49 PM
Author: oceanbeach

Date: 8/7/2006 10:45:13 PM
Author: strmrdr
they can sometimes be a problem but a good vendor can weed out the problem stones.


What are the crown and pavilion angles?

Crown angle is 34.3, and pavilion angle is 40.6. thanks!

that is one id likely pass on but it might be a nice diamond,,,, it depends on whats in the 40.6 average and the optical symmetry.

 

[oceanbeach]

Date: 8/7/2006 11:00:03 PM
Author: strmrdr

Date: 8/7/2006 10:46:49 PM

Author: oceanbeach

Date: 8/7/2006 10:45:13 PM

Author: strmrdr

they can sometimes be a problem but a good vendor can weed out the problem stones.



What are the crown and pavilion angles?

Crown angle is 34.3, and pavilion angle is 40.6. thanks!

that is one id likely pass on but it might be a nice diamond,,,, it depends on whats in the 40.6 average and the optical symmetry.

humm..... It''s tough! I have no idea what''s good and what''s not other than looking at the ideal cut table. Well, I guess it''s the best if I look at it in person?! Thank you for your opinion!

 

[strmrdr]

a in person look would be a good idea.. check it up close if its a problem stone it will look too dark close but great from 3 feet.

 

[aljdewey]

Date: 8/7/2006 10:43:21 PM
Author:oceanbeach

I was told by a vendor that stones that score under 1.0 (HCA) tend to have very poor real life performance. Is this true?!

No, it''s not true as stated.

It is true that *some* stones that score under 1.0 may not be top-shelf performers....but it''s totally not true of ALL stones that score less than 1.0. It''s absolutely, unequivocally UNTRUE that "stones that scores under 1.0 tend to have very poor real life performance." That''s an absolute statement, and it''s incorrect and misleading. Shame on that vendor.

If I''d have listened to the vendor who said that to you, I''d have missed out on a TOTAL beauty. My e-ring scored a 0.9......and my respected appraiser with more than 25 years experience vouched for my diamond as "blazing" with exceptional light performance.

Sometimes, in the haste to caution, people can sometimes overstate, and I think that''s what happened in this situation. It''s fair and good to advise you to be mindful that *some* stones scoring below a 1.0 *might not* perform very well. (The concern, by the way, is a potential lack of contrast.)

It''s a notable warning, but it''s not absolute. I hate these kind of Chicken-Little-Beware-of-This-or-That statements.

They don''t help anyone, and they undermine the credibility of the one uttering them.

 

[Garry H (Cut Nut)]

Bolocks.

A tolkowsky with 56% table and thin (not too thin) girdle is HCA 0.8

 

[oceanbeach]

Date: 8/8/2006 1:09:50 AM
Author: Garry H (Cut Nut)
Bolocks.


A tolkowsky with 56% table and thin (not too thin) girdle is HCA 0.8

Good to hear this! Thank you,

 

[oceanbeach]

Date: 8/7/2006 11:26:13 PM
Author: strmrdr
a in person look would be a good idea.. check it up close if its a problem stone it will look too dark close but great from 3 feet.

Well, I think I will check it out in person. I would assume that an appraiser can easily tell me if that is a problem stone, not a great performer, correct? ...luck of contrast etc...


aljdewey, thanks for your comment; this is helpful!!

 

[Regular Guy]

Dear Oceanbeach,

Here's a couple ideas for you, I say, while drawing with a twig in the sand:

1) This thread may be helpful in general, but difficult to apply in particular

2) Though I'd recommend taking your diamond to a qualified appraiser, my own guess is that most will be hard pressed to give you the kind of nuanced analysis you're looking for here.

3) That is, perhaps, with the exception of one gemologist, who happens to be in Long Island, and may be one technically sophisticated enough to discern the differences you'd be interested in.

4) If he happens to be the same vendor who even gave you the warning, voila. See #5

5) I just created this...if you go this far, be our venturer, and modify in a way that will help you the most.

Consider creating a document that will allow him and you to work together peaceably, efficiently, and to your benefit:

I, so & so, will get your help to appraise this diamond, providing the technical analysis I need to make a purchase decision. In getting this help, we agree I will:

a) not be able to purchase a diamond from you;

b) not be able to purchase a diamond from you within 100 days;

c) not be able to purchase a diamond from you within 35 days;

d) thank you for your services, regardless of the outcome

Signed, so & so.

-----------------

Just some thoughts,

 

[Dee*Jay]

Ocean, you can use all the wonderful programs in the world, but your best tool is your own eye.

I recently came across a stone that I liked A LOT in person but when I came home and put the specs in the HCA it scored ONLY .6 (gasp!). How could that be? How could I *like* a stone with only a .6 score? Was I blind? Was I stupid? Were all these hours (and belive me there have been MANY!) on Pricescope been for not?

NO!

I ended up buying this stone and it's gorgeous. So much so, as a matter of fact, that I'm having a hard time giving it up in terms of a trade to a larger diamond, which was the ultimate goal.

Go see it. If you love it, buy it!

 

[strmrdr]

Date: 8/8/2006 6:25:22 AM
Author: oceanbeach

Date: 8/7/2006 11:26:13 PM
Author: strmrdr
a in person look would be a good idea.. check it up close if its a problem stone it will look too dark close but great from 3 feet.

Well, I think I will check it out in person. I would assume that an appraiser can easily tell me if that is a problem stone, not a great performer, correct? ...luck of contrast etc...


aljdewey, thanks for your comment; this is helpful!!

yes an appraiser who is used to dealing with ideal cut diamonds can tell you if its an issue in 10 seconds flat as can the better PS dealers.

 

[strmrdr]

Date: 8/8/2006 8:01:37 AM
Author: Regular Guy
Dear Oceanbeach,

Here''s a couple ideas for you, I say, while drawing with a twig in the sand:

1) This thread may be helpful in general, but difficult to apply in particular

2) Though I''d recommend taking your diamond to a qualified appraiser, my own guess is that most will be hard pressed to give you the kind of nuanced analysis you''re looking for here.

3) That is, perhaps, with the exception of one gemologist, who happens to be in Long Island, and may be one technically sophisticated enough to discern the differences you''d be interested in.

4) If he happens to be the same vendor who even gave you the warning, voila. See #5

5) I just created this...if you go this far, be our venturer, and modify in a way that will help you the most.

Consider creating a document that will allow him and you to work together peaceably, efficiently, and to your benefit:

I, so & so, will get your help to appraise this diamond, providing the technical analysis I need to make a purchase decision. In getting this help, we agree I will:

a) not be able to purchase a diamond from you;

b) not be able to purchase a diamond from you within 100 days;

c) not be able to purchase a diamond from you within 35 days;

d) thank you for your services, regardless of the outcome

Signed, so & so.

-----------------

Just some thoughts,

Dont add hogwash.
This one is into the terrotory where it can be an issue and an appraisser or vendor used to dealing with ideal cut diamonds can tell quickly if its an issue.

 

[strmrdr]

Date: 8/8/2006 9:20:08 AM
Author: Dee*Jay
Go see it. If you love it, buy it!

excellent advice.

 

[Regular Guy]

Date: 8/8/2006 10:13:29 AM
Author: strmrdr

Date: 8/8/2006 6:25:22 AM
Author: oceanbeach

Date: 8/7/2006 11:26:13 PM
Author: strmrdr
a in person look would be a good idea.. check it up close if its a problem stone it will look too dark close but great from 3 feet.

Well, I think I will check it out in person. I would assume that an appraiser can easily tell me if that is a problem stone, not a great performer, correct? ...luck of contrast etc...


aljdewey, thanks for your comment; this is helpful!!

yes an appraiser who is used to dealing with ideal cut diamonds can tell you if its an issue in 10 seconds flat as can the better PS dealers.

Storm,

Our appraisers even on this board have so rarely entered these discussions to even acknowledge the territory of this issue...

This is a problem in and of itself, if you want their comment.

Second, that their analysis would be black & white, problem or not, I do not believe it.

Third, without the reference to one (or more, as would be availabie with a vendor) reference stones, that also do and do not have the sort of problems descrribed, I am hard pressed to visualize the assistance an appraiser would routinely provide on this.

But, I''d like to be better informed, and welcome the opportunity for that.

 

[fire&ice]

Well, I have a stone that scores under 1 HCA. It''s a kickin ball of fire. Also, keep in mind that HCA has a margin of error and with it some absolutes that most programs have.

See - if it speaks to you - don''t worry about it.

 

[aljdewey]

Date: 8/8/2006 9:20:08 AM
Author: Dee*Jay
Ocean, you can use all the wonderful programs in the world, but your best tool is your own eye.

I recently came across a stone that I liked A LOT in person but when I came home and put the specs in the HCA it scored ONLY .6 (gasp!). How could that be? How could I *like* a stone with only a .6 score? Was I blind? Was I stupid? Were all these hours (and belive me there have been MANY!) on Pricescope been for not?

NO!

I ended up buying this stone and it''s gorgeous. So much so, as a matter of fact, that I''m having a hard time giving it up in terms of a trade to a larger diamond, which was the ultimate goal.

Go see it. If you love it, buy it!

A hearty, hearty AMEN to this comment by Dee Jay.

The numbers are a *guideline*, but they shouldn''t replace your eye, and they aren''t gospel.

 

[Rhino]

I''d agree with Alj''s comments. If a vendor/person made a blanket statement that all stones under 1.0 are poor visual performers this is a misleading comment. It is a known fact however that there are quite a few angle combinations that score under a 1.0 on the HCA make neither AGS nor GIA ideal cut grades and should be approached with more caution than stones that fall between 1.0 and 2.0.

40.6 is a threshold angle in the GIA system. All other measurements (crown angles, total depth, lower halves, stars, etc.) will impact the overall performance. As the folks here suggested a good idea would be to view it, perhaps alongside another with 40.8-41 degree pavilion angles and in diffuse daylight.

Kind Regards,

 

[Regular Guy]

Scratch Long Island.

Any other appraisers hale & hearty?

 

[aljdewey]

Date: 8/8/2006 2:20:20 PM
Author: Rhino

It is a known fact however that there are quite a few angle combinations that score under a 1.0 on the HCA make neither AGS nor GIA ideal cut grades and should be approached with more caution than stones that fall between 1.0 and 2.0.

40.6 is a threshold angle in the GIA system. All other measurements (crown angles, total depth, lower halves, stars, etc.) will impact the overall performance. As the folks here suggested a good idea would be to view it, perhaps alongside another with 40.8-41 degree pavilion angles and in diffuse daylight.

Kind Regards,

Yes, but since all other measurements on GIA stones are rounded, it''s tough to discern exactly what that impact will be. It''s so arbitrary that they even round up odd numbered pavilion angles just because they are odd numbered.

Pavilion angle is rounded to the nearest multiple of 0.2°
Pavilion angles ending in odd numbers are always rounded UP, for example 40.7° would be rounded to 40.8°

 

[Rhino]

LOL... Ira.

Let me add one thing here as far as our research/observation/study into the GIA/AGS cut grading systems and the HCA which is a fact. The lower the HCA score, the more they DO indeed tend to be poorer performers and for the most part do fall outside of the most conservative labs specs for ideal.

It should be pointed out that the HCA results are only one man''s opinion which in quite a few circumstances disagrees with majority opinion/conservative grading labs. Garry is partial/biased towards shallow angled diamonds and this partiality/bias is reflected in the HCA. There''s nothing wrong with that but consumers should be aware of it when consulting this tool.

A blanket and absolute statement such as ALL stones under 1.0 are poor performers is as Alj has said ... misleading. Equally as misleading as if someone were to advise a consumer that ALL diamonds that score under a 2.0 on the HCA are ideal cuts.

Just wanted to clarify.

Peace,

 

[Rhino]

Hello Alj,

Hope this post finds you well. Thoughts below.

Date: 8/8/2006 2:40:48 PM
Author: aljdewey

Date: 8/8/2006 2:20:20 PM
Author: Rhino

It is a known fact however that there are quite a few angle combinations that score under a 1.0 on the HCA make neither AGS nor GIA ideal cut grades and should be approached with more caution than stones that fall between 1.0 and 2.0.

40.6 is a threshold angle in the GIA system. All other measurements (crown angles, total depth, lower halves, stars, etc.) will impact the overall performance. As the folks here suggested a good idea would be to view it, perhaps alongside another with 40.8-41 degree pavilion angles and in diffuse daylight.

Kind Regards,

Yes, but since all other measurements on GIA stones are rounded, it''s tough to discern exactly what that impact will be. It''s so arbitrary that they even round up odd numbered pavilion angles just because they are odd numbered.

Pavilion angle is rounded to the nearest multiple of 0.2°
Pavilion angles ending in odd numbers are always rounded UP, for example 40.7° would be rounded to 40.8°

Understood. You know I''m a stickler for detail and I sincerely understand where you''re coming from on this. I am always in favor of more detail. When I was talking with the researchers at GIA about this issue, they put it to me this way. I was asked how many Sarin''s I''ve seen on the same diamond. Since I have Sarin, Helium, OGI here I can see the results from these 3 devices plus we have the measurements on the AGS Reports. I''ve also seen results and compared to Dave, Rich, Bill and other appraisers who use Sarin''s . Oftentimes the measurements are +/- a tenth of a degree. We''ve even seen AGS measurements off by .2 degrees before as well (though this is not the norm). Considering the variances from one machine to another (even as good as these are), I was asked ... are we doing the consumer/trade a service or disservice considering no two Sarin''s are the same?

I started thinking of the repercussions. Ie ... say if Bill''s Sarin was not identical to GIA''s? What if Dave''s was .02 degrees off? Nobody would trust anyone else''s Sarin except GIA''s. GIA did not view this as being practical and considering the variations from one Sarin to the next I understand where they''re coming from on this issue. I hope this helps you better understand why they took that stance.

Kind regards,

 

[Regular Guy]

Hey Rhino,

Since you''re turning down an appraiser assignment I was getting you set up for, could you consider doing me a small favor.

Follow this thread on the point you are making about 0 - 1, and share your thoughts. On the theory of the linearity of performance, it would seem to provide a protocol for assessment numerically, even if only either Helium or quality 3D sarin could execute it.

 

[WinkHPD]

Gary can correct me on this if I am wrong, but I believe my memory of the details is correct. Below a pavilion angle of 40.4 the light performance drops quickly. If you have a stone listed as 40.4 then some of the facets will be below that and some above that. With many of the diamonds cut today having variences of as high as 0.4 to 0.5 you will then have a stone with a listed pavilion angle of 40.4 that actually has some of the facets with angles as low as 39.1 to 40.0.

With a tightly cut diamond having variences of 0.1 to 0.2 you would actually have a much better looking diamond, still, you probably would like the averages to be no lower than 40.6 and that only if the diamond is tightly cut with very low tolerances for variation.

Having in my possession many diamonds with HCA''s below 1.0 I can emphatically state that the statement that stones below an HCA score of 1.0 are poor performers is pure bunk. They have the potential to be if not cut to tight tolerances, but they can be stunning as well.

Wink

 

[Garry H (Cut Nut)]

Date: 8/8/2006 3:20:16 PM
Author: Wink
Gary can correct me on this if I am wrong, but I believe my memory of the details is correct. Below a pavilion angle of 40.4 the light performance drops quickly. If you have a stone listed as 40.4 then some of the facets will be below that and some above that. With many of the diamonds cut today having variences of as high as 0.4 to 0.5 you will then have a stone with a listed pavilion angle of 40.4 that actually has some of the facets with angles as low as 39.1 to 40.0.

With a tightly cut diamond having variences of 0.1 to 0.2 you would actually have a much better looking diamond, still, you probably would like the averages to be no lower than 40.6 and that only if the diamond is tightly cut with very low tolerances for variation.

Having in my possession many diamonds with HCA''s below 1.0 I can emphatically state that the statement that stones below an HCA score of 1.0 are poor performers is pure bunk. They have the potential to be if not cut to tight tolerances, but they can be stunning as well.

Wink

Wink a stone with a big variance more often than not will suffer more from leakage on the steep side - say a 41 that is 40.5 to 41.5 than a stone that has a few facets that are a bit shallow and only upset the apple cart when you stick your head into an unreasonable very close viewing position that is rarely used.

 

[oceanbeach]

All,

Thank you very much for the great advice and education! These are all helpful to me. I''ve decided to see the stone with my own eyes. : )

P.S. By the way, just to clarify...the vendor didn''t tell me that ALL of them have poor performance; they told me "TEND TO have poor performance..."

Thanks!

 

[Rhino]

Date: 8/8/2006 3:15:06 PM
Author: Regular Guy
Hey Rhino,

Since you''re turning down an appraiser assignment I was getting you set up for, could you consider doing me a small favor.

Follow this thread on the point you are making about 0 - 1, and share your thoughts. On the theory of the linearity of performance, it would seem to provide a protocol for assessment numerically, even if only either Helium or quality 3D sarin could execute it.

Hi Ira,

I''ll check it out. Thanks for the heads up.

 

[Regular Guy]

Date: 8/8/2006 3:59:50 PM
Author: Garry H (Cut Nut)

Date: 8/8/2006 3:20:16 PM
Author: Wink
Gary can correct me on this if I am wrong, but I believe my memory of the details is correct. Below a pavilion angle of 40.4 the light performance drops quickly. If you have a stone listed as 40.4 then some of the facets will be below that and some above that. With many of the diamonds cut today having variences of as high as 0.4 to 0.5 you will then have a stone with a listed pavilion angle of 40.4 that actually has some of the facets with angles as low as 39.1 to 40.0.

With a tightly cut diamond having variences of 0.1 to 0.2 you would actually have a much better looking diamond, still, you probably would like the averages to be no lower than 40.6 and that only if the diamond is tightly cut with very low tolerances for variation.

Having in my possession many diamonds with HCA''s below 1.0 I can emphatically state that the statement that stones below an HCA score of 1.0 are poor performers is pure bunk. They have the potential to be if not cut to tight tolerances, but they can be stunning as well.

Wink

Wink a stone with a big variance more often than not will suffer more from leakage on the steep side - say a 41 that is 40.5 to 41.5 than a stone that has a few facets that are a bit shallow and only upset the apple cart when you stick your head into an unreasonable very close viewing position that is rarely used.

Garry, I noticed you''d largely been quiet on this idea. Sounds like your content to sit back and let folks take pot shots at 0 - 1 particularly, and join them in part, maintaining 1 - 2 is frequently more well liked. I had thought we had a good theory going for the degradation that can be accounted for, for poor performers at 0 - 1, but sounds like this does not really make sense to you. I think Wink did briefly nail this supposition here.

Jonathan, your read is still valued. Your first paragraph above does run counter to what Paul has shared, a respected cutter here. And I don''t agree with your second paragraph. I think the HCA is entirely consistent with AGS''s new parameters, and if you raise the bar a bit, accounting for viewing distance (is that right?), the systems might match 1 to 1.

 

[aljdewey]

Date: 8/8/2006 3:09:41 PM
Author: Rhino

Understood. You know I''m a stickler for detail and I sincerely understand where you''re coming from on this. I am always in favor of more detail. When I was talking with the researchers at GIA about this issue, they put it to me this way. I was asked how many Sarin''s I''ve seen on the same diamond. Since I have Sarin, Helium, OGI here I can see the results from these 3 devices plus we have the measurements on the AGS Reports. I''ve also seen results and compared to Dave, Rich, Bill and other appraisers who use Sarin''s . Oftentimes the measurements are +/- a tenth of a degree. We''ve even seen AGS measurements off by .2 degrees before as well (though this is not the norm). Considering the variances from one machine to another (even as good as these are), I was asked ... are we doing the consumer/trade a service or disservice considering no two Sarin''s are the same?

I started thinking of the repercussions. Ie ... say if Bill''s Sarin was not identical to GIA''s? What if Dave''s was .02 degrees off? Nobody would trust anyone else''s Sarin except GIA''s. GIA did not view this as being practical and considering the variations from one Sarin to the next I understand where they''re coming from on this issue. I hope this helps you better understand why they took that stance.

I understand that explanation, but I personally believe the logic is faulty.

I get it.......since everyone''s machine varies a little, why sweat the small stuff? But they aren''t looking at the aggregate effect.

Going to your example.....Bill''s Sarin isn''t identical to GIA''s Sarin. So, Bill''s Sarin reports a 40.7 crown angle and GIA reflects a 40.9. However, since GIA doesn''t like even numbers, now they round that up to 41. They further amplified the difference by rounding.

Then, on the same diamond, Bill''s Sarin shows a 34.6 crown. GIA shows 34.7, but they round it up to 35. There''s another amplified difference.

By the time you get done amplifying the already inherent differences times all the things they round, the data becomes meaningless.

Their approach is akin to saying "since all devices measure with a degree of error anyway, it''s not important to be exact at all." I disagree with this line of thinking. The fact that nothing can be 100% perfect all the time isn''t a valid reason to get sloppy and lenient on the standards.

We can acknowledge that perfection isn''t achievable, but the act of at least striving for it produces better results than throwing hands in the air and saying "ah - close enough."