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GIA Excellent = HCA 6!

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phoenixgirl

Ideal_Rock
Joined
Mar 20, 2003
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3,390
I was designing myself imaginary rings and found this diamond:

1.44 GIA excellent that scores a 6.0 on the HCA. Yikes, I pity the poor person who buys this thinking it''s a well cut stone!
 
Wow, I checked that cos I couldn't really believe it (sorry!). That's incredible. With those measurements, it doesn't even look round!
Maybe Gary or another expert can chime in and explain this. How on earth can this stone get an excellent cut grade? It is an error in the grading report?

Just goes to show how lucky we are to have tools such as the HCA and IS! And PS!!!!
9.gif
 
6.gif
But if I am not mistaken if you look at the HCA it still falls within the boundaries for a GIA excellent
 
Doesn''t GIA grade cut based on human observation. Apparently someone at GIA thought it looked "excellent".
Maybe that crown angle and pavilion work well with eachother even though they''re both waay outside of the ideal range.

Not a stone I''d pick or recommend but who knows...
 
Hmm, the listing also says it is an "Ideal" cut stone!
 
I''m really wondering what this stone looks like!!!
Would this be like a bright stone without much fire? (the crown and pavilion angles still confuse me)
 
small ring of death that while it decreases performance is likely not 2 eye visible to a large degree.
Its on the extreme edge of GIA EX and not something id buy.
The predicted AGS score is 5
This is the problem with simple number based systems on top of an imperfect observation based grading system with the trade doing the observation.

418335.jpg
 
Date: 3/8/2008 7:30:16 PM
Author: elle_chris
Doesn''t GIA grade cut based on human observation. Apparently someone at GIA thought it looked ''excellent''.
Maybe that crown angle and pavilion work well with eachother even though they''re both waay outside of the ideal range.

Not a stone I''d pick or recommend but who knows...
GIA does not look at diamonds with the naked eye for cut quality (other than for polish, sym and girdle thickness, all under magnification).

They did a study where a number (?100- 500? cant remember) looked at some stones in controled light which makes many fancy cuts look better than rounds. Then they applied those proportions to a very similar system to HCA (which I have a patent for).
GIA and a group of my associates have had words over the flaws in their approach as reported here
http://journal.pricescope.com/Articles/50/1/Letter-to-the-Editor-of-the-Australian-Gemmologist.aspx
 
Date: 3/8/2008 8:41:16 PM
Author: strmrdr
small ring of death that while it decreases performance is likely not 2 eye visible to a large degree.
Its on the extreme edge of GIA EX and not something id buy.
The predicted AGS score is 5
This is the problem with simple number based systems on top of an imperfect observation based grading system with the trade doing the observation.
I think you would see it easily Storm

xyzxyzyxz.jpg
 
Date: 3/9/2008 3:25:54 AM
Author: Garry H (Cut Nut)

Date: 3/8/2008 8:41:16 PM
Author: strmrdr
small ring of death that while it decreases performance is likely not 2 eye visible to a large degree.
Its on the extreme edge of GIA EX and not something id buy.
The predicted AGS score is 5
This is the problem with simple number based systems on top of an imperfect observation based grading system with the trade doing the observation.
I think you would see it easily Storm
in a bezel yea in a high 4 prong it would be harder too see.
 
true ;-)
but it will still look bad when it is dirty
 
Date: 3/9/2008 4:18:00 AM
Author: Garry H (Cut Nut)
true ;-)
but it will still look bad when it is dirty
yea....
 
Date: 3/9/2008 3:47:41 AM
Author: strmrdr

Date: 3/9/2008 3:25:54 AM
Author: Garry H (Cut Nut)


Date: 3/8/2008 8:41:16 PM
Author: strmrdr
small ring of death that while it decreases performance is likely not 2 eye visible to a large degree.
Its on the extreme edge of GIA EX and not something id buy.
The predicted AGS score is 5
This is the problem with simple number based systems on top of an imperfect observation based grading system with the trade doing the observation.
I think you would see it easily Storm
in a bezel yea in a high 4 prong it would be harder too see.
Question..., how would this C & P combination look "virtually" if the lgf''s would be painted and shortened and to 70%?
 
Date: 3/9/2008 4:23:06 AM
Author: DiaGem

Date: 3/9/2008 3:47:41 AM
Author: strmrdr


Date: 3/9/2008 3:25:54 AM
Author: Garry H (Cut Nut)



Date: 3/8/2008 8:41:16 PM
Author: strmrdr
small ring of death that while it decreases performance is likely not 2 eye visible to a large degree.
Its on the extreme edge of GIA EX and not something id buy.
The predicted AGS score is 5
This is the problem with simple number based systems on top of an imperfect observation based grading system with the trade doing the observation.
I think you would see it easily Storm
in a bezel yea in a high 4 prong it would be harder too see.
Question..., how would this C & P combination look ''virtually'' if the lgf''s would be painted and shortened and to 70%?
you can improve it, but not save its life DG
And by improving it GIA would bing you for "brillianteering"
 
Date: 3/9/2008 4:29:31 AM
Author: Garry H (Cut Nut)

Date: 3/9/2008 4:23:06 AM
Author: DiaGem


Date: 3/9/2008 3:47:41 AM
Author: strmrdr



Date: 3/9/2008 3:25:54 AM
Author: Garry H (Cut Nut)




Date: 3/8/2008 8:41:16 PM
Author: strmrdr
small ring of death that while it decreases performance is likely not 2 eye visible to a large degree.
Its on the extreme edge of GIA EX and not something id buy.
The predicted AGS score is 5
This is the problem with simple number based systems on top of an imperfect observation based grading system with the trade doing the observation.
I think you would see it easily Storm
in a bezel yea in a high 4 prong it would be harder too see.
Question..., how would this C & P combination look ''virtually'' if the lgf''s would be painted and shortened and to 70%?
you can improve it, but not save its life DG
And by improving it GIA would bing you for ''brillianteering''
If it gets improved and at the same time gets "binged" for brillianteering...,
33.gif
, why? Because of the lgf''s length? (out of EX parameters?)

Garry..., what if this Dia. had a 54% table? Would it be improved even more?
 
Date: 3/9/2008 4:37:40 AM
Author: DiaGem

Date: 3/9/2008 4:29:31 AM
Author: Garry H (Cut Nut)


Date: 3/9/2008 4:23:06 AM
Author: DiaGem



Date: 3/9/2008 3:47:41 AM
Author: strmrdr




Date: 3/9/2008 3:25:54 AM
Author: Garry H (Cut Nut)





Date: 3/8/2008 8:41:16 PM
Author: strmrdr
small ring of death that while it decreases performance is likely not 2 eye visible to a large degree.
Its on the extreme edge of GIA EX and not something id buy.
The predicted AGS score is 5
This is the problem with simple number based systems on top of an imperfect observation based grading system with the trade doing the observation.
I think you would see it easily Storm
in a bezel yea in a high 4 prong it would be harder too see.
Question..., how would this C & P combination look ''virtually'' if the lgf''s would be painted and shortened and to 70%?
you can improve it, but not save its life DG
And by improving it GIA would bing you for ''brillianteering''
If it gets improved and at the same time gets ''binged'' for brillianteering...,
33.gif
, why? Because of the lgf''s length? (out of EX parameters?)

Garry..., what if this Dia. had a 54% table? Would it be improved even more?
Dinged, not binged
2.gif
GIA have a 1 size fits all brilanteering (painting and digging) rule - even if it helps the appearance of the stone.
54% would help, but the proportoins problem can not be made good by FAQ Pricescope standards with anything other than a pavilion or crown angle lowering.
 
Date: 3/9/2008 6:34:48 AM
Author: Garry H (Cut Nut)

Date: 3/9/2008 4:37:40 AM
Author: DiaGem


Date: 3/9/2008 4:29:31 AM
Author: Garry H (Cut Nut)



Date: 3/9/2008 4:23:06 AM
Author: DiaGem




Date: 3/9/2008 3:47:41 AM
Author: strmrdr





Date: 3/9/2008 3:25:54 AM
Author: Garry H (Cut Nut)






Date: 3/8/2008 8:41:16 PM
Author: strmrdr
small ring of death that while it decreases performance is likely not 2 eye visible to a large degree.
Its on the extreme edge of GIA EX and not something id buy.
The predicted AGS score is 5
This is the problem with simple number based systems on top of an imperfect observation based grading system with the trade doing the observation.
I think you would see it easily Storm
in a bezel yea in a high 4 prong it would be harder too see.
Question..., how would this C & P combination look ''virtually'' if the lgf''s would be painted and shortened and to 70%?
you can improve it, but not save its life DG
And by improving it GIA would bing you for ''brillianteering''
If it gets improved and at the same time gets ''binged'' for brillianteering...,
33.gif
, why? Because of the lgf''s length? (out of EX parameters?)

Garry..., what if this Dia. had a 54% table? Would it be improved even more?
Dinged, not binged
2.gif
GIA have a 1 size fits all brilanteering (painting and digging) rule - even if it helps the appearance of the stone.
54% would help, but the proportoins problem can not be made good by FAQ Pricescope standards with anything other than a pavilion or crown angle lowering.
Why..., do you think C33.5 combined with P41.8 is too much of a problematic proportion?
I know 41.8 is deep..., but it should be good with a certain CA? Maybe 33 deg. (or shallower?)
 
Date: 3/9/2008 7:33:27 AM
Author: DiaGem
Why..., do you think C33.5 combined with P41.8 is too much of a problematic proportion?
I know 41.8 is deep..., but it should be good with a certain CA? Maybe 33 deg. (or shallower?)
c of 31.2 too 31.5 would bring it into a potential AGS1with a marginal for durability girdle(thin girdle shallow crown combo), with a med girdle it would never get below ags3 getting dinged for spread.
 
Date: 3/9/2008 8:57:48 AM
Author: strmrdr

Date: 3/9/2008 7:33:27 AM
Author: DiaGem
Why..., do you think C33.5 combined with P41.8 is too much of a problematic proportion?
I know 41.8 is deep..., but it should be good with a certain CA? Maybe 33 deg. (or shallower?)
c of 31.2 too 31.5 would bring it into a potential AGS1with a marginal for durability girdle(thin girdle shallow crown combo), with a med girdle it would never get below ags3 getting dinged for spread.
Even though a C33.5, P41.8, lgf''s @ 70%, 54%T would probably be a better looking stone than any 31.5-2 degree crown?
 
Date: 3/9/2008 9:38:23 AM
Author: DiaGem
Even though a C33.5, P41.8, lgf''s @ 70%, 54%T would probably be a better looking stone than any 31.5-2 degree crown?
Would need some painting too bring the uppers in and would get kicked down on contrast.
The cutting charts are useless for this combo and it would have too be ran in the software but im guessing somewhere around ags6 with no painting....

33541854.jpg
 
41.8/30/54/70 would make ags1 maybe... again it would have too be ran in the software...

304187054.jpg
 
Date: 3/9/2008 10:06:37 AM
Author: strmrdr

Date: 3/9/2008 9:38:23 AM
Author: DiaGem
Even though a C33.5, P41.8, lgf''s @ 70%, 54%T would probably be a better looking stone than any 31.5-2 degree crown?
Would need some painting too bring the uppers in and would get kicked down on contrast.
The cutting charts are useless for this combo and it would have too be ran in the software but im guessing somewhere around ags6 with no painting....
Storm..., please paint the lgf''s and show me a face-up of a virtual Diamond in office lighting or any other...
 
33.5/41.8/54/70 crown painted

GIA would downgrade this level of painting too VG, AGS might or might not downgrade it.
But it would take a hit for spread and contrast anyway. Maybe AGS3?

33541854painted.jpg
 
lowers painted, both ags and gia would hammer this much lower painting most likely.

33541854LGpainted.jpg
 
Same lighting Garry used above and the same I use too show asscher patterns which is worst case with rounds.

33541854LGpainted2.jpg
 
crown painting comparison.

33541854painted2.jpg
 
dc office lighting crown painting

33541854painted3a.jpg
 
dc office lowers painted both 41.8p 33.5c 54T 70lgf

33541854LGpainted3.jpg
 
Date: 3/9/2008 10:34:15 AM
Author: strmrdr
dc office lowers painted both 41.8p 33.5c 54T 70lgf
How is going to look with a 40.8 P (not painted)? I guess much better!
1.gif
 
here ya go... ags1 takes a hit in dispersion due too the shallow upper girdles most likely.

33540854.jpg
 
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