Garry H: Question about the Use of the HCA

[henearly89]

I am looking at this stone:

http://www.bluenile.com/build-your-own-diamond-ring?&pid=LD01029163&builder=BYOR&forceStep=DIAMONDS_STEP

It comes back as a 1.3 TIC on the HCA. I have requested a more detailed Sarin report, but Blue Nile does not provide idealscope images.

Given a Sarin and a GIA certification, how reliable are the HCA readings? Does an HCA score based on a Sarin report remove some of the fallibility of the GIA numbers? Would you feel confident enough that a 1.3 TIC is truly an ideal cut diamond?

I have been shying away from Blue Nile because I prefer to see an idealscope, but the convenience of buying the diamond from where I am getting my setting, combined with the fact that the other vendors do not have any diamonds that meet these specifications, have me leaning toward trusting the Sarin and the HCA and getting it appraised after the fact.

 

[Lorelei]

Date: 2/7/2010 2:33:24 PM
Author:henearly89
I am looking at this stone:

http://www.bluenile.com/build-your-own-diamond-ring?&pid=LD01029163&builder=BYOR&forceStep=DIAMONDS_STEP

It comes back as a 1.3 TIC on the HCA. I have requested a more detailed Sarin report, but Blue Nile does not provide idealscope images.

Given a Sarin and a GIA certification, how reliable are the HCA readings? Does an HCA score based on a Sarin report remove some of the fallibility of the GIA numbers? Would you feel confident enough that a 1.3 TIC is truly an ideal cut diamond?

I have been shying away from Blue Nile because I prefer to see an idealscope, but the convenience of buying the diamond from where I am getting my setting, combined with the fact that the other vendors do not have any diamonds that meet these specifications, have me leaning toward trusting the Sarin and the HCA and getting it appraised after the fact.

Hi Henearly

Just to start you off until Garry comes along, BN will not to the best of my knowledge be able to provide a Sarin report, also the numbers should be safe even with GIA rounding and as far as can be told without images it should be a lovely stone.

Garry might pop up presently and give you more info, keep an eye out for him and bump your thread if you spot him!

 

[henearly89]

Blue Nile has already provided several Sarin reports, you just have to convince them you won''t buy from them otherwise. They are currently in the process of getting me one for this stone.

I may take the diamond to Good Old Gold for an appraisal and full lab workup (since I live in the area). I just don''t want to go through the hassle without feeling reasonably confident I may have a winner.

I REALLY wish Blue Nile did an Idealscope and/or BrilliantScope/Gemex.

 

[Lorelei]

Date: 2/7/2010 3:00:30 PM
Author: henearly89
Blue Nile has already provided several Sarin reports, you just have to convince them you won't buy from them otherwise. They are currently in the process of getting me one for this stone.

I may take the diamond to Good Old Gold for an appraisal and full lab workup (since I live in the area). I just don't want to go through the hassle without feeling reasonably confident I may have a winner.

I REALLY wish Blue Nile did an Idealscope and/or BrilliantScope/Gemex.

Have BN actually given you Sarin reports in the past? If so, this must be a new service they are offering. I know we had a poster a little while ago that asked them for a Sarin report and was under the impression that they would get one for them, but if I remember rightly they couldn't in the end. But if they are offering this service then it would be good to know so that we can get more info on some of their diamonds, it would be very useful especially with fancy shapes.

 

[JulieN]

I once did a small sample test to see how GIA rounding would affect HCA scores; for "actual" HCA scores vs GIA rounded HCA scores: most often, a stone that had an actual HCA score of
The caveats to HCA IS the assumption that the stone is perfectly symmetrical!

If the Sarin ranges are relatively tight and and it matches up with GIA rounding (to eliminate the possiblity of Sarin calibration being too off to be useful) then HCA can be used for its INTENDED purpose: elimination.

However, I would only say "HCA="1.3 --"> 'ideal' cut stone" if the assumptions of HCA are TRUE, most importantly, that it is symmetrical. I will note that a PA average of 40.6-40.9 is "safe" enough that an HCA score of less than 2 with those pavilion angles, and tight Sarin ranges would most probably result in an ideal cut stone.

 

[henearly89]

Date: 2/7/2010 3:49:53 PM
Author: JulieN
I once did a small sample test to see how GIA rounding would affect HCA scores; for ''actual'' HCA scores vs GIA rounded HCA scores: most often, a stone that had an actual HCA score of
The caveats to HCA IS the assumption that the stone is perfectly symmetrical!

If the Sarin ranges are relatively tight and and it matches up with GIA rounding (to eliminate the possiblity of Sarin calibration being too off to be useful) then HCA can be used for its INTENDED purpose: elimination.

However, I would only say ''HCA=1.3 --> ''ideal'' cut stone'' if the assumptions of HCA are TRUE, most importantly, that it is symmetrical. I will note that a PA average of 40.6-40.9 is ''safe'' enough that an HCA score of less than 2 with those pavilion angles, and tight Sarin ranges would most probably result in an ideal cut stone.

I guess one of my questions, then, is what ranges need to be tight and how would you define tight? I know the crown angle shouldn''t vary by too much, but how much variance before we begin to say that the symmetrical assumption fails? What about for other things like diameter, pavillion angle, etc. How much variance would you tolerant in order to trust the HCA, for Elimination purposes.

 

[henearly89]

Yes, Blue Nile has given me an ACTUAL Sarin report (I think this one is a little less detailed). Here is what they gave me for a DIFFERENT diamond. I will post the Sarin for the new diamond tomorrow or on Tuesday and maybe someone can help me interpret how to interpret the variance for the purpose of HCA reliability.

 

[stone-cold11]

Date: 2/7/2010 5:18:33 PM
Author: henearly89

Date: 2/7/2010 3:49:53 PM

Author: JulieN

I once did a small sample test to see how GIA rounding would affect HCA scores; for 'actual' HCA scores vs GIA rounded HCA scores: most often, a stone that had an actual HCA score of
The caveats to HCA IS the assumption that the stone is perfectly symmetrical!

If the Sarin ranges are relatively tight and and it matches up with GIA rounding (to eliminate the possiblity of Sarin calibration being too off to be useful) then HCA can be used for its INTENDED purpose: elimination.

However, I would only say 'HCA=1.3 --> 'ideal' cut stone' if the assumptions of HCA are TRUE, most importantly, that it is symmetrical. I will note that a PA average of 40.6-40.9 is 'safe' enough that an HCA score of less than 2 with those pavilion angles, and tight Sarin ranges would most probably result in an ideal cut stone.

I guess one of my questions, then, is what ranges need to be tight and how would you define tight? I know the crown angle shouldn't vary by too much, but how much variance before we begin to say that the symmetrical assumption fails? What about for other things like diameter, pavillion angle, etc. How much variance would you tolerant in order to trust the HCA, for Elimination purposes.

Just dump the limit of each range and if all the extreme still falls into below HCA 2, then it should be good, unless the lower half is too short.

This sarin report is still the average report, will prefer a detail report like GOG's helium report.

 

[henearly89]

That was my inclination. I plan to do that when I get the Sarin. As you said, it would help if this Sarin were more detailed.

 

[Garry H (Cut Nut)]

You are using HCA as a selection tool. It is a blunt rejection tool and it has not rejected this diamond.
now use an appriser if BN will not even look at it through an ideal-scope for you.
It should be nice

 

[Lorelei]

Date: 2/7/2010 11:34:48 PM
Author: Garry H (Cut Nut)
You are using HCA as a selection tool. It is a blunt rejection tool and it has not rejected this diamond.
now use an appriser if BN will not even look at it through an ideal-scope for you.
It should be nice

In a nutshell.

 

[Garry H (Cut Nut)]

Date: 2/8/2010 7:10:51 AM
Author: Lorelei

Date: 2/7/2010 11:34:48 PM
Author: Garry H (Cut Nut)
You are using HCA as a selection tool. It is a blunt rejection tool and it has not rejected this diamond.
now use an appriser if BN will not even look at it through an ideal-scope for you.
It should be nice

In a nutshell.

Like a cut nut, or a rough nut

 

[Lorelei]

Date: 2/9/2010 7:21:34 AM
Author: Garry H (Cut Nut)

Date: 2/8/2010 7:10:51 AM
Author: Lorelei

Date: 2/7/2010 11:34:48 PM
Author: Garry H (Cut Nut)
You are using HCA as a selection tool. It is a blunt rejection tool and it has not rejected this diamond.
now use an appriser if BN will not even look at it through an ideal-scope for you.
It should be nice

In a nutshell.

Like a cut nut, or a rough nut

Definitely a cut nut!!

 

[Laila619]

Just chiming in to say that Blue Nile does offer SARIN reports if they can get one. They gave me one last summer on a stone I was interested in.

 

[Lorelei]

Date: 2/9/2010 9:40:16 AM
Author: Laila619
Just chiming in to say that Blue Nile does offer SARIN reports if they can get one. They gave me one last summer on a stone I was interested in.

Yes, I was able to verify that, on round diamonds only apparently they will offer Sarin, not fancy shapes.