Low HCA number

[OPA Rocks]

I am considering a stone with a low HCA number (0.4). Here is the specs on the stone:

1.15ct, H, SI1, Girdle M-STK, VG Pol, EX Sym, Depth 61.1%, Tale 56%, Crwn Ang 34.5deg, Pav Ang 40.5deg ~$4950

What are the problems with the an HCA number that is below 1? It claims to have excellent light return, fire, and scintillation, but it only a GIA very good cut. I would like to hear what some of you think of this particular stone.

Thanks!

 

[Paul-Antwerp]

The PS-community has developed a common wisdom that one should be careful with stones scoring under 1.0 on HCA. I totally disagree.

The HCA is a rejection-tool, and after a number of stones passed the HCA-test, one should look further.

With stones scoring under 1.0, they are cut closer to the edge, and could be stellar performers. However, around these specific proportion-areas, the slightest lack of care of the cutter can have a bigger negative effect. So, if you check further, and especially, if you see that the stone has a very good optical symmetry, there is nothing wrong with this stone.

GIA, in its observation studies, did not pay attention to the further detail of the stones, and consequently, they had little stones with optical symmetry in the observation. Therefore, such proportion-sets ended up in their VG-grade, while a good cutter would possibly produce a ''better than excellent'' stone with the same average proportions.

Sorry if this is confusing.

Live long,

 

[Garry H (Cut Nut)]

Date: 10/5/2007 2:29:14 AM
Author:OPA Rocks
I am considering a stone with a low HCA number (0.4). Here is the specs on the stone:

1.15ct, H, SI1, Girdle M-STK, VG Pol, EX Sym, Depth 61.1%, Tale 56%, Crwn Ang 34.5deg, Pav Ang 40.5deg ~$4950

What are the problems with the an HCA number that is below 1? It claims to have excellent light return, fire, and scintillation, but it only a GIA very good cut. I would like to hear what some of you think of this particular stone.

Thanks!

As Paul wrote - this is a potential - next can you get an ideal-scope image?

 

[WorkingHardforSmallRewards]

HCA is a weeding tool.

 

[stebbo]

Date: 10/5/2007 3:48:45 AM
Author: WorkingHardforSmallRewards
HCA is a weeding tool.

Can I use it in my garden?

You couldn''t resist could you WHFSR!

 

[Regular Guy]

Date: 10/5/2007 2:43:44 AM
Author: Paul-Antwerp

With stones scoring under 1.0, they are cut closer to the edge, and could be stellar performers. However, around these specific proportion-areas, the slightest lack of care of the cutter can have a bigger negative effect. So, if you check further, and especially, if you see that the stone has a very good optical symmetry, there is nothing wrong with this stone.

I don''t think the optical symmetry needing to be especially checked for tightness with the number is low in the 0-2 range matches Garry''s write up:

"Stones near the center of the red region (the lowest scores) are least affected by symmetry variations. Alternatively hearts and arrows diamonds, which have excellent optical symmetry, but often HCA scores around 2, may out-perform diamonds with lesser symmetry and lower HCA scores...."

But the "closer to the edge" story has its own idea and message...

 

[Paul-Antwerp]

Date: 10/5/2007 6:09:13 AM
Author: Regular Guy

Date: 10/5/2007 2:43:44 AM
Author: Paul-Antwerp

With stones scoring under 1.0, they are cut closer to the edge, and could be stellar performers. However, around these specific proportion-areas, the slightest lack of care of the cutter can have a bigger negative effect. So, if you check further, and especially, if you see that the stone has a very good optical symmetry, there is nothing wrong with this stone.

I don''t think the optical symmetry needing to be especially checked for tightness with the number is low in the 0-2 range matches Garry''s write up:

''Stones near the center of the red region (the lowest scores) are least affected by symmetry variations. Alternatively hearts and arrows diamonds, which have excellent optical symmetry, but often HCA scores around 2, may out-perform diamonds with lesser symmetry and lower HCA scores....''

But the ''closer to the edge'' story has its own idea and message...

Indeed, Garry and I do not always agree.

Live long,

 

[Lord Summerisle]

Wouldnt say any problem with a 0.4 HCA score.

Lady S'' diamond is D59.9 T57 C34.8 P40.5 which scored 0.4, and is a stunner

like Garry askes, do you have a Ideal Scope or Aset image of the diamond?

 

[kcoursolle]

A low HCA score doesn''t suggest any problems. However, it doesn''t necessarly suggest that you should select the stone either. You need to go beyond now and look at images, IS images, etc. in order to see whether it is the stone to select.

 

[Rhino]

Regardless of personal opinions there are value reasons to consider as well. God forbid you should ever find yourself in the position of wanting to sell this or trade it in etc., a GIA Ex will always be in higher demand than a GIA VG despite the HCA score. While we all love PS, PS is only a microcosm of diamond trading in the world and the HCA is no recognized standard in any laboratory nor in this industry. I''m not sure if you''re considering this or even care but is food for thought. My professional advice to you would be to visually compare this side by side to a GIA Ex or AGS Ideal and if you don''t see any difference and if you find its worth the savings go for it. I would emphasize to make observations not only in jewelry store spot lighting but natural or simulated diffuse day lighting. Jewelry store spot lighting will flatter this combo but in natural diffuse daylight, there is a likely chance it may be darker when you compare it to an Ex or Ideal. I''d be curious to hear your report if you indeed make this observation.

Regards,

 

[OPA Rocks]

Thank you all for your help so far. My problem is that I am shopping online, so I have not seen these stones in person yet. I have asked my sales associate for any idealscope images they might have, but they have been closed the past few days in observance of a few religious holidays. If I get anything like this I will post it immeadiatly to get your reactions.

I was also thrown by the fact that this stone is not a GIA EX. I have another stone that is a GIA EX that I would like your opinions on:


1.12ct, H, SI1, Girdle M-STK, VG Pol, VG Sym, Depth 60.4%, Tale 59%, Crwn Ang 35 deg, Pav Ang 40.8 deg ~$4820 HCA 1.9

OR

1.21ct, H, SI1, Girdle M-STK, VG Pol, EX Sym, Depth 62.4%, Tale 56%, Crwn Ang 34.5 deg, Pav Ang 41.0 deg ~$5580 HCA 1.9

 

[JohnQuixote]

What lab graded this diamond? GIA gives pavilion in even tenths (they round) so a GIA report wouldn't have 40.5 listed.
Does it have an accompanying Sarin report?

Date: 10/5/2007 5:28:33 PM
Author: OPA Rocks

I was also thrown by the fact that this stone is not a GIA EX.

You might buoyed to know that the same gem could very well receive AGS0 in light performance if it has good optical symmetry, appropriate minors and precise cutting (tip of the hat to Paul's post above). An ideal-scope image would help immensely.

Now you might be asking yourself... "Self, how can it be a potential AGS0 but GIA VG?"

It's because the systems are weighted somewhat differently. Here is an example of how a few common systems (GIA, AGSL, HCA and AGA) ‘overlap’ – and don’t.

Pavilion angle is usually good for showing where the ‘center’ of different systems lies:For 53-58% tables, pavilion angles 40.6-41.0 have the greatest approval cross-system. The AGS cut guidelines suggest most 0 candidates right in that range. The HCA and AGA prefer the shallow side (and a bit lower). The GIA system prefers the steep side (and higher). Coupled with this table and crown angle, the 40.5 PA is still a candidate for the top AGSL grade but falls just outside GIA's EX.

This doesn’t make the diamond less beautiful, particularly a VG at the shallow border of EX, which is a system more weighted toward steep/deep stones than the other systems. They chose a cutoff and it's between 40.6 and 40.4. Any tangible visual difference would be a matter of what your eyes see. Technically, the caution with pavilions at the shallow side (like this 40.5 average) is that the shallower you go the more obstruction will occur; darkness caused by the observer blocking light, especially at a close viewing distance.This is why the HCA recommends shallow-pavilioned stones for pendants/earrings, which are worn in such a manner that obstruction is less of an influence - and ‘older people rings’ - because oldsters cannot focus as closely as youngsters so they keep their rings at more of a distance. See the graphic on this page.

The GIA VG probably comes with a small discount for what could be no visible difference between it and EX. If you're not planning to re-sell this diamond in the future it could be a winner visually and in terms of the pocketbook...if the dealer has a long-term trade-up policy you're good even if you re-sell. If going with "mind clean" numbers is the goal I see you have a couple of other candidates on deck. Will you be able to get ideal-scope images for these?

 

[strmrdr]

As you can see there is a wide swing of opinions on diamonds with 40.5 pavilions, the real bottom line is eyeballs, either comparing them to other well cut diamonds or an in person evaluation by someone skilled in the art and science of high performance diamonds.

 

[Garry H (Cut Nut)]

Date: 10/5/2007 5:28:33 PM
Author: OPA Rocks
Thank you all for your help so far. My problem is that I am shopping online, so I have not seen these stones in person yet. I have asked my sales associate for any idealscope images they might have, but they have been closed the past few days in observance of a few religious holidays. If I get anything like this I will post it immeadiatly to get your reactions.

I was also thrown by the fact that this stone is not a GIA EX. I have another stone that is a GIA EX that I would like your opinions on:


1.12ct, H, SI1, Girdle M-STK, VG Pol, VG Sym, Depth 60.4%, Tale 59%, Crwn Ang 35 deg, Pav Ang 40.8 deg ~$4820 HCA 1.9

OR

1.21ct, H, SI1, Girdle M-STK, VG Pol, EX Sym, Depth 62.4%, Tale 56%, Crwn Ang 34.5 deg, Pav Ang 41.0 deg ~$5580 HCA 1.9

You have my opinion already on these 2 - next step is as always - get an ideal-scope image for us please