Confused about HCA Results

[cutey TT]

Hi All.

I just entered the following #s into the HCA tool and got 3.2 - Very Good - Worth buying if the price is right (VG, G, G, VG):

Table = 56%
Depth = 61.8%
Crown Angle = 34.5
Pavilion Angle = 41.2

Then when I used the crown height (15%) and pavilion depth (43.5%) instead, I got an HCA result of 1.8 - Excellent within TIC range (Ex, VG, VG, VG).

Then I entered all of the above into AGA DIY Cut Grading tool, and got a final grade of 1A (all values were 1A except pavilion depth 43.5% = 1B). It seems that the outlying value is the 41.2 pavilion angle. Since the AGA tool does not ask for this value, it seems that the stone was not "penalized." Whereas the first HCA value took this into account, therefore resulting in the (not so desirable) 3.2 score.

Can some of you experts chime in and tell me what you think of this stone based on these values? The vendor can call in this stone for me, but I''m not really sure if I should pass based on the initial 3.2 HCA score. Help!?

 

[cutey TT]

Just so this is easier to see:

Depth = 61.8%
Table = 56%
Crown Angle = 34.5 Crown Height = 15%
Pavilion Angle = 41.2 Pavilion Depth = 43.5%
Star Length = 55%
Lower Half = 80%
Girdle = Thin- Medium, Faceted

 

[whatmeworry]

Is that a GIA diamond? Since the angles are rounded, I wonder if the % are a more accurate description of the diamond.

 

[cutey TT]

It is a GIA diamond.

 

[Ellen]

If it''s a really well cut stone, it could be great. That being said, we have no idea how tightly cut it is, so all one can really say is, it''s got potential. An IS would be really nice, could the vendor do that for you?

 

[cutey TT]

The vendor would have to call it in, since it''s still part of the virtual inventory. We''re still looking at other options, so I''m not sure that I want to call this stone in per se. With that being said though, the stone is within budget, and supposedly an eye-clean SI1 (per the supplier).

 

[Ellen]

cutey, I realize you''d have to call it in, I was just wondering if an IS is an option with that vendor. Not all do it.

If you''re not done looking, then I''d say keep it on the back burner, just in case.

 

[cutey TT]

Date: 1/25/2008 5:18:05 PM
Author: Ellen
cutey, I realize you''d have to call it in, I was just wondering if an IS is an option with that vendor. Not all do it.

If you''re not done looking, then I''d say keep it on the back burner, just in case.

Ellen. Yep, WF is the vendor. They are recommending other stones however, one 3.03 G VS2 with a higher HCA score. There are two other H VS2 stones, but I''m not sure that I want an H in a 3+ carater. The 34.5/41.2 in question is an F SI1.

My sales rep is checking to see if WF would be willing to put their lifetime upgrade on it, assuming we called it in, I liked it, and a purchase ensued, etc.

 

[Ellen]

Ah, ok. In that case, I'd trust WF and have a look at their other recommendations first. When you say higher score on the G, do you actually mean lower/better?


And oooh la la, I can't wait to see this!

 

[Garry H (Cut Nut)]

On the HCA page their is a link that says "angles are more accurate"
https://www.pricescope.com/tutor/angl_vs_dpt.asp

 

[whatmeworry]

Date: 1/25/2008 7:22:09 PM
Author: Garry H (Cut Nut)
On the HCA page their is a link that says ''angles are more accurate''
https://www.pricescope.com/tutor/angl_vs_dpt.asp

Garry, what if the angles are from GIA (rounded). Would the % be more accurate in this case?

 

[Garry H (Cut Nut)]

Date: 1/25/2008 7:28:57 PM
Author: whatmeworry

Date: 1/25/2008 7:22:09 PM
Author: Garry H (Cut Nut)
On the HCA page their is a link that says ''angles are more accurate''
https://www.pricescope.com/tutor/angl_vs_dpt.asp

Garry, what if the angles are from GIA (rounded). Would the % be more accurate in this case?

No - read the bit about measurement innacuracy, culet etc

And on top of that WhatWorry from 42% to 43.5% is 4 steps. This is 6 steps in degrees of 0.2 degrees

In this case 43.5% covers 40.86 to 41.19 degrees.

And you are thinking aha - it could be closer to 40.11 degrees - but you would be wrong beause of culet and the measuring system which is reported to be Sarin. We regularly see evidence of GIA measurement innaccurucy on depth with Sarin because most likely of the method Sarin use to "construct" the slope angles. you can see this in the grading report survey that we did a couple of years ago. Last week I heard of a cutter who had a diamond marked down from Excellent because of just such an error. Helium and a micrometer both proved GIA was incorrect. The cutter must pay GIA to have this error corrected (assuming they admit fault and give in).

 

[Rhino]

optical symmetry can really make a difference in such a stone.

 

[Garry H (Cut Nut)]

Date: 1/25/2008 8:11:37 PM
Author: Rhino
optical symmetry can really make a difference in such a stone.

Optical symmetry is vital for such a stone.
A little painting helps too.

And cleaning it because it will suffer more than a lower HCA stone when dirty.
boiling water, ammonia and detergent with a good scrub with tooth brush behind the stone and a good rinse and dry

 

[cutey TT]

Date: 1/25/2008 6:52:10 PM
Author: Ellen
Ah, ok. In that case, I''d trust WF and have a look at their other recommendations first. When you say higher score on the G, do you actually mean lower/better?


And oooh la la, I can''t wait to see this!

Sorry yes, the G VS2 has a lower / better HCA score. I forget, either 1.5 or 1.7. However, it is also $6K over my desired budget...

 

[diamondseeker2006]

I am totally convinced that the perfect stone is always over budget! That seems to be the way it usually works!