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Confused about HCA

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alamb

Rough_Rock
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I''ve been doing quite a bit of research and am very close to purchasing a stone. The stone rates .8 on HCA. I thought that the lower the better, so I was quite pleased this stone came out this way as it is beautiful in person. However, upon reading another thread on here. Someone was worried that their stone only rated .6 on HCA and therefore may have contrast or not have contrast, I''m not sure. In any case, now I''m really confused as I didn''t know your stone could be actually too low on HCA. Can anyone shed any light on this?

Thank-you!
Allison
 

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Regular Guy

Ideal_Rock
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Agreed.

Also, just for fun, upper right, under search, try entering:

low AND HCA
 

starryeyed

Ideal_Rock
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Hi Alamb. Sometimes a stone that is really low falls in that super red zone on the chart, just outside of the AGS Ideal and GIA Excellent zones. What does the cert say in terms of cut grade?
 

alamb

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The stone cut is AGS Ideal, excellent polish and symetry, so should I be okay? What is the contrast issue?
 

starryeyed

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You should be ok Allison. I''m not exactly sure what the contrast issue would be other than the idea of the diamond not having enough darks to show arrows or something. Do you have an ideal-scope image of the diamond? That would probably show you if there are any issues....
 

Regular Guy

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Date: 12/7/2006 6:46:38 PM
Author: alamb
The stone cut is AGS Ideal, excellent polish and symetry, so should I be okay? What is the contrast issue?
Do you know if the AGS is also zero for light performance? You can read about this here.

Again, probably fine either way, but if it's a newer cert, AGS0 generally trumps even poorer HCA scores, when they conflict.
 

strmrdr

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whats the average crown and pavilion angles off the cert?
 

:)

Brilliant_Rock
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Date: 12/7/2006 5:24:22 PM
Author:alamb
I''ve been doing quite a bit of research and am very close to purchasing a stone. The stone rates .8 on HCA. I thought that the lower the better, so I was quite pleased this stone came out this way as it is beautiful in person. However, upon reading another thread on here. Someone was worried that their stone only rated .6 on HCA and therefore may have contrast or not have contrast, I''m not sure. In any case, now I''m really confused as I didn''t know your stone could be actually too low on HCA. Can anyone shed any light on this?

Thank-you!
Allison
That''s what counts!
 

Rhino

Ideal_Rock
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If the stone is an AGS ideal it''s likely you''re safe with regards to light performance however there are varying appearances within the ideal grade which some prefer over others. It''d be interesting to see either an ASET image or both ASET image and the crown/pavilion angle combo on it.

Peace,
 

Rhino

Ideal_Rock
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Date: 12/7/2006 9:12:58 PM
Author: :)

Date: 12/7/2006 5:24:22 PM
Author:alamb
I''ve been doing quite a bit of research and am very close to purchasing a stone. The stone rates .8 on HCA. I thought that the lower the better, so I was quite pleased this stone came out this way as it is beautiful in person. However, upon reading another thread on here. Someone was worried that their stone only rated .6 on HCA and therefore may have contrast or not have contrast, I''m not sure. In any case, now I''m really confused as I didn''t know your stone could be actually too low on HCA. Can anyone shed any light on this?

Thank-you!
Allison
That''s what counts!
And an amen to that. ;-)
 

alamb

Rough_Rock
Joined
Dec 2, 2006
Messages
54
THank you everyone for your feedback! In answer to your questions:

1) The AGS does not give light performance as it is an older certificate.
2) I do not have an ideal scope image of it.
3) The specs are as follows:

3.03
E color
Crown angle 35.7
Pav angle 40.4
Depth 62.5
Table 56
HCA - EX, EX, Ex, VG - total .8

Let me know what you guys think!
 

Regular Guy

Ideal_Rock
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I think the tool itself, upper right, cut advisor under tools, provides a nice self contained descroption.
 

Rhino

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Date: 12/8/2006 7:11:59 AM
Author: alamb
THank you everyone for your feedback! In answer to your questions:

1) The AGS does not give light performance as it is an older certificate.
2) I do not have an ideal scope image of it.
3) The specs are as follows:

3.03
E color
Crown angle 35.7
Pav angle 40.4
Depth 62.5
Table 56
HCA - EX, EX, Ex, VG - total .8

Let me know what you guys think!
This is a proportion set that falls in what might considered "the controversial zone".

The reason I say this is because this proportion set in GIA's system will not make Ex grade for reasons of light performance (35.5/40.4/56) and when I run this model in AGS Performance Grading Software it comes out to a 1, not for reasons of light performance but proportion factors.

The 40.4 pavilion angle concerns me. It should be tempered ok with the 35.7 crown angle but generally when the pavilion angles run on the shallow end like this, it generally causes an overdarkening of the mains in common viewing environments which I can also see in the DiamCalc software.

It's a cusp stone that's impossible to call without a physical examination and analysis of the stone.

The HCA favors shallow angled pavilions and reflects a personal preference of Garry's but I personally don't find these to be the brightest stones. They will however be brighter than steeper angled combos. I'd like to see this pavilion angle *at least* brought to 40.6 and better yet 40.8. It'd cause the mains to light up better assuming a nice symmetrical stone.

Chances are it wouldn't get ideal in the new systems of cut grading with either GIA or AGS but nobody would know for sure without an accurately scanned model of it. My advice is if you like who you're doing business with see if they can get you a stone with a more recent GIA or AGS cut grade which takes light performance into account. This way you'll be able to make a more fair comparison. You may still prefer this one but you'll never know until you see. Good luck on your hunt.

Kind regards,
 

strmrdr

Super_Ideal_Rock
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Sounds like a nice fic that plays on the borders of the AGS0 and GIA ex range.

If you like diamonds on the fiery side then its just fine in my opinion as long as it has decent optical symmetry and longer lower girdle facets.
 

Rhino

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Date: 12/8/2006 4:56:53 PM
Author: strmrdr
Sounds like a nice fic that plays on the borders of the AGS0 and GIA ex range.

If you like diamonds on the fiery side then its just fine in my opinion as long as it has decent optical symmetry and longer lower girdle facets.
Good point. Long lower girdle facets will place a heavier emphasis on the light coming off the pavilion halves than they would the mains. If the mains are too short it''ll place the emphasis on the darker mains. Too bad the older AGS Reports didn''t include minor facet info.
 

strmrdr

Super_Ideal_Rock
Joined
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Look at the stone is difused lighting and up close (10-12 inches) and if it looks good to you then I think your set.
What your checking for is huge dark zones(arrows are fine is they arent too big).
 

alamb

Rough_Rock
Joined
Dec 2, 2006
Messages
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strmrdr - Ok, now your talking way over my head! I''m not even sure what you mean by Long lower girdle facets and how I would know if it has it or not. Sorry, I''ve been doing a lot of research, but i''m still a newbie I guess. I also looked at the stone away from the jewelry store lighting and wasn''t a little less impressed than before.

Rhino - Thanks so much for the pavilion angle information. I think you may be correct about finding a stone with a new certificate. I actually went back to look at the stone again today for the 15th time and I don''t feel as married to it as I did before. I sort of had my mind set on VS2 or better but this is an SI1. It is eye clean from the top but not from the side. I saw on the chart what you indicated as it was a bit out of the GIA and AGS zone for ideal cut. I really want the best, most absolute ideal cut I can find so I think I''m going to go back to the drawing board.

Thanks again - I appreciate the help very much.

Allison
 

Rhino

Ideal_Rock
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Date: 12/8/2006 8:54:42 PM
Author: alamb

Rhino - Thanks so much for the pavilion angle information. I think you may be correct about finding a stone with a new certificate. I actually went back to look at the stone again today for the 15th time and I don''t feel as married to it as I did before. I sort of had my mind set on VS2 or better but this is an SI1. It is eye clean from the top but not from the side. I saw on the chart what you indicated as it was a bit out of the GIA and AGS zone for ideal cut. I really want the best, most absolute ideal cut I can find so I think I''m going to go back to the drawing board.

Thanks again - I appreciate the help very much.

Allison
No prob Allison. I wouldn''t let the VS2-SI1 issue perturb you unless it''s a mind clean thing with ya. If you found top notch optics in an SI1 you should seriously consider that unless seeing an inclusion the side bothers ya. In a 3ct honker it is easier to see into its facets particularly from the side/profile view but then you also have to consider how rare the finest cuts are in that size range. Sacrificing to an SI1 for top cut isn''t a bad compromise IMO. Of course if you can find your VS2 all the better.

Amongst the realm of GIA Ex and AGS Ideal''s there are some varying appearances within each of these grades too so keep a sharp eye when you make your comparisons. GIA is a bit more liberal on steep angled combinations while AGS is a bit more liberal on the shallow angled combos. It is however possible to find stones that fall in the zenith of both and those are what most would consider "the cherry zone".


Good luck on your hunt Allison. You have a great crowd of people here who are happy to offer their input and help.

Kind regards,
 
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