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acbutk

Rough_Rock
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Feb 1, 2007
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32
Do you live and die by the HCA? I''ve read the usage description and warnings. I don''t understand why a GIA excellent cut grade would not score well. Is it not enough to trust that an excellent cut grade will give excellent brilliance? I am not an expert. This website seems to be filled with expert advice, but practically speaking, is it safe to believe that a diamond with an excellent cut, very good symmetry, and excellent polish will look wonderful to a commoner like myself? Thank you.
 

acbutk

Rough_Rock
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Feb 1, 2007
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32
I seriously would like to know how much weight should be placed on the HCA score?
 

kenny

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
28,208
Viaualize a target with smaller circles inside larger circles.

Let's just say GIA Excellent is not the smallest circle in the middle.

(There is some overlap but I think of AGS's top cut grade, and a good HCA score, as an even smaller circle closer to the center, the goal.)

This commoner shoots for the bullseye.
 

acbutk

Rough_Rock
Joined
Feb 1, 2007
Messages
32
Thanks, Kenny. My next question would be: If a diamond with a lower cut grade scores higher on the hca then a diamond with a higher cut grade, what is a person to do?
 

kenny

Super_Ideal_Rock
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Tell us more about the stone you are considering.

What are the:
Depth %
Table %
Crown Angle
Pavilion Angle
Girdle %

If you give us this info the experts here can tell you more.
 

ILikeBond

Shiny_Rock
Joined
Nov 20, 2006
Messages
312
I think your (understandible) confusion stems from a misconception about the HCA. It is really a tool used to weed out likely bad performers, not to actually choose the stone itself. In that way, it sets a floor, not a ceiling. For instance, no one here would say that, without more, a stone that rates 0.9 is better than a stone that rates 1.4. It just doesn''t work that way. The HCA tells you which stones to throw out based on proportions, but for stones that show potential based on proprotions, you still need to evaluate them in other ways to determine (a) if a stone is a winner; and (b) which of two stones that are both potential "winners" performs better.

Hope that helps.

PS - a lot of people feel that there''s a "sweet spot" in the HCA around 1-1.5, and that stones in this range will actually perform better than, say, a 0.6, which you occasionally see. If you post info about stones you''re looking at - including what they score on the HCA, which is just one piece of info, but not the end-all, be-all - lots of people here can help you understand what the quality of the stone(s) is/are, why its that way, and ultimately help you choose.
 

acbutk

Rough_Rock
Joined
Feb 1, 2007
Messages
32
#1) .90, H, SI-1, 61.9/58, VG/EX, crown 34.5, pavilion 41.0, girdle medium to thick.

#2) .90, H. SI-1, 62.8/57, EX/VG, crown 35.5, pavilion 41.0, girdle medium to slightly thick.
 

ILikeBond

Shiny_Rock
Joined
Nov 20, 2006
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312
Date: 2/5/2007 4:59:39 PM
Author: acbutk
#1) .90, H, SI-1, 61.9/58, VG/EX, crown 34.5, pavilion 41.0, girdle medium to thick.

#2) .90, H. SI-1, 62.8/57, EX/VG, crown 35.5, pavilion 41.0, girdle medium to slightly thick.
I''d personally pass on both, #1 b/c the table is too big and variation in the girdle is too much, and #2 b/c the crown angle is too big.

If you give your budget and color/clarity requirements, lots of people here could help you locate some nice stones to choose from.
 

acbutk

Rough_Rock
Joined
Feb 1, 2007
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32
I thought that these specs. were pretty close to that of an AGS-0, which seems to be the epitome of a well cut diamond. So, I just don''t understand.
 

ILikeBond

Shiny_Rock
Joined
Nov 20, 2006
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312
Date: 2/5/2007 5:29:38 PM
Author: acbutk
I thought that these specs. were pretty close to that of an AGS-0, which seems to be the epitome of a well cut diamond. So, I just don''t understand.
They are pretty close, and either or both diamonds may be very beautiful. However, people around here (like me!) knitpick, and there''s a lot of options out there in your range, so why not try to get the absolute best (for instance, a stone where both the symmetry and polish are excellent)?

Here''s one to consider - .852 H/VS2 - $3,667.20 with the wire discount.
 

Ellen

Super_Ideal_Rock
Joined
Jan 13, 2006
Messages
24,426
Date: 2/5/2007 6:28:57 PM
Author: JulieN
ideal scope
I agree with Julie, if you're really interested in one these, you need an IS image. I would bet the second is definitely going to show leakage.

My opinion on the HCA, is, it's good for a preliminary judging of a diamond. It will quickly weed out undesirables. It cannot truly predict how a stone will act, as it doesn't know ALL the cutting details.

Once you get a good score (under 2, although that will change in the future), you need more info, IS, ASET, Sarin. Then take it from there, regardless of who gaded it.


That stone ILikeBond posted is very nice.
 

RockDoc

Ideal_Rock
Joined
Aug 15, 2000
Messages
2,509
Date: 2/5/2007 5:22:40 PM
Author: ILikeBond

Date: 2/5/2007 4:59:39 PM
Author: acbutk
#1) .90, H, SI-1, 61.9/58, VG/EX, crown 34.5, pavilion 41.0, girdle medium to thick.

#2) .90, H. SI-1, 62.8/57, EX/VG, crown 35.5, pavilion 41.0, girdle medium to slightly thick.
I''d personally pass on both, #1 b/c the table is too big and variation in the girdle is too much, and #2 b/c the crown angle is too big.

If you give your budget and color/clarity requirements, lots of people here could help you locate some nice stones to choose from.
It appears that the stones above were graded by GIA.

GIA''s cut grade system only considers proportions, which in and of itself is no guarantee of the light performance.

IN addition, the proportions reported in GIA''s profile are first made with a machine that has some variaince to its measurements/ then those measurements are AVERAGED, and then they are rounded up or down.

AGS''s measurements are made with similar measurement scanners ( although GIA MAY be using OGI scanners as compared to AGS use of Sarin/Helium scanners which are more accurate) so as a result proportions that appear the same may actually not be. AGS does report averages as well.

As a suggestion if you are really influenced by the lower prices that GIA graded stones are, you might ask the seller for the .srn or .stl files and use Diamond Calc to get a "clearer" and more accurate assessment of the stones'' actual proportions.

Rockdoc
 
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