HCA

[diablo]

Two round diamonds: One scores 1.2 on HCA and is not H&A and the other scores 1.7 but is H&A. What I really want to know is can a diamond with poor H&A symmetry score well on the HCA or does the HCA give a good level of assurance about optical symmetry?

 

[diablo]

Oooops sorry folks. The topic seems to have been discussed ad nauseum in the archives so no need to waste time on replying. I can research it there.

Thanks.

 

[Garry H (Cut Nut)]

ood
HCA has no idea of symmetry
it works well to reject stones that can not look good - it is very good at rejecting H&A"S THAT HAVE BEEN CUT TOO DEEPLY>

 

[diablo]

Thanks Garry. I''m sure you''re sick and tired of answering the same questions but here goes.............

The non-H&A diamond with the HCA score of 1.2 has an external symmetry grade of "Ideal" from AGSL. Would the combination of a good HCA score and ideal external symmetry tend to indicate good internal symmetry?

 

[Garry H (Cut Nut)]

An AGS ideal symmetry can not be bad (although there were some bad stones because of some tricks - but they know about it now and i think they stop them going through).
1.2 should be perfectly acceptable and comparable to your eye to an H&A''s 1.7

 

[valeria101]

Date: 12/13/2004 4:28:19 AM
Author: diablo
Thanks Garry. I'm sure you're sick and tired of answering the same questions but here goes.............

The non-H&A diamond with the HCA score of 1.2 has an external symmetry grade of 'Ideal' from AGSL. Would the combination of a good HCA score and ideal external symmetry tend to indicate good internal symmetry?

H&A is just one of many kinds of pretty pictures

that a round brilliant may show inside.

You may want to take a look over THIS page on Good Old Gold.com (unless done already... but what can I know?).

One example there may answer your Q: IMO, the least one could reproach to this diamond is symmetry (optical or meet-point), but... see what's missing ?

Gia Ex-EX "Harts and Flowers?"

Also, There was a recent thread about how the symmetry grade relates to optics LINK - you may want to take a look.

All in all, I could not swear that all this theory is perfectly relevant to the one diamond in your hand. Those grades and numbers are only an approximation to what the stone looks, and I hope some of those examples show just how many versions of readind between the lines are there !

Will you be able to see and have this diamond appraised during some return period ? Or get more accurate info than numbers from the seller in the mentime ?

 

[diablo]

The numbers I have from the AGS report are:
Carat: 1.19
Dimensions: 6.88 x 6.94 x 4.19
Colour: G
Clarity: SI1
Cut: AGS0
Culet: pointed
Flourescence: negligible
Depth: 60.7%
Table: 56%
Crown angle: 34.4
Pavillion angle: 40.9
Girdle: thin to medium
HCA: 1.3 (not 1.2 as I said earlier)

I will have 30 days to return. Nothing jumps out at me as being wrong but maybe I''m missing something.

 

[Garry H (Cut Nut)]

Ana that is a lousy H&A''s - it is leaking like a seive!

 

[valeria101]

Date: 12/13/2004 6:202 AM
Author: Garry H (Cut Nut)
Ana that is a lousy H&A''s - it is leaking like a seive!

Yes Sir!

I was a bit confused by the original question: it seems to concern the symmetry grade but it was not clear to me what this grade was expected to predict - either H&A looks or light return or both. So the louse has Ex symmetry, no H&A and ouch brilliance - just for ref.

If there was a tutorial page on how optical symmetry and the namesake grade on lab reports relate... it would fit here. In absence, the thread on facet yaw with its technical refferences came to mind.

Your answer pins the question, of course.

 

[JohnQuixote]

Date: 12/13/2004 7:21:58 AM
Author: valeria101

If there was a tutorial page on how optical symmetry and the namesake grade on lab reports relate... it would fit here.

Ana - would these descriptors help?

Symmetry - Graded/Meet Point versus Physical and Optical