Help! HCA 1.0, but GIA VG cut, what gives?!

[snowstorm]

This''s my first post so please go easy. What a great community here.

I got my eyes on a couple of stones from an Internet vendor (Abazias) and am pretty confused. One was a GIA EX but scored a 2.5 on HCA and the other was a GIA VG but score a almost perfect 1.0. I can''t see the stones and can only rely on the numbers from the cert.

Can someone help me make sense of what''s going on? Should I trust HCA or GIA? Which is a better stone?

Stone 1
GIA cut = VG
Polish/Sym = VG/EX
D VS2
Table = 59%
Depth = 59.6%
Crown = 33.5 degrees
Pavilion = 40.6 degrees
HCA 1.0 (see attached image)
Stone 2
GIA cut = EX
Polish/Sym = EX/EX
F VS2
Table = 58%
Depth = 60.4%
Crown = 33.5 degrees
Pavilion = 41.6 degrees
HCA 2.5 (see attached image)

Can anyone shed some light on this?

 

[JulieN]

#2: is that 41.2 degrees pavilion angle, or 41.6?

for 1, as you can see, it is outside of GIA's "box" for the Excellent grade.

It would be a very nice stone for a pendant or earring, but it is not as suitable for a ring.

Read this carefully http://diamonds.pricescope.com/ideal.asp It's sort of the HCA user's manual (very short.)

 

[neatfreak]

There's a reason that the HCA is a REJECTION tool, NOT a selection tool. Anything under 2 warrants further consideration, but isn't an automatic winner. As Julie mentioned the first stone isn't a great ering stone because of how it reflects light. It is not an ideal cut in the traditional sense of the word.

And GIA isn't known for their tight cut grading which is why some GIA Ex's aren't that great.

With the HCA you want something under 2 AND within the white AGS box if possible.

 

[snowstorm]

Thanks for the thought everyone, I am totally new at this.

The pavilion angle on the 2nd stone be 41.2 and not 41.6 degrees.
I am looking for a diamond for a ring, so would the 1st one be no good?
Would the 2nd one with 2.5 HCA be acceptable. I can''t seem to find something that is <2 and withing the white ASG box at the moment...

 

[John P]

Date: 12/4/2008 9:22:36 PM
Author:snowstorm

Can someone help me make sense of what''s going on? Should I trust HCA or GIA? Which is a better stone?

Stone 1
GIA cut = VG
Polish/Sym = VG/EX
D VS2
Table = 59%
Depth = 59.6%
Crown = 33.5 degrees
Pavilion = 40.6 degrees
HCA 1.0 (see attached image)

Stone 2
GIA cut = EX
Polish/Sym = EX/EX
F VS2
Table = 58%
Depth = 60.4%
Crown = 33.5 degrees
Pavilion = 41.6 degrees
HCA 2.5 (see attached image)

Can anyone shed some light on this?

Sure. 59/40.6/33.5 earns HCA EX. It is also a candidate for AGS Ideal performance as long as the lower halves and stars are nominal. However it''s at the GIA threshold of EX/VG - falling into VG.

Why? Because the GIA cut grading system is skewed deeper than the HCA, AGA and AGS systems. This is why your second stone, with 58/41.6/33.5, can earn GIA EX (which is insanity), but the HCA and AGS systems will not reward it (AGS4).

If Julie''s supposition about 41.2 is correct... 58/41.2/33.5 also scores GIA EX (this is not nearly as scandalous as 41.6) but is not a top performer according to HCA or AGS - although predicted at AGS 1-2 which is not too bad at all.

 

[snowstorm]

The 2nd stone is 41.2 and not 41.6, my bad when typing in the numbers.

I know it is hard to say for sure without seeing the stone, but if you were to advise on a diamond for a ring with just the info here, what would be a better pick? (note that stone 1 is VG polish and stone 2 is EX polish, but I don''t think that matters too much)

Stone 1 VS2 D 59%/59.6%/33.5/40.6 HCA 1
Stone 2 VS2 F 58%/60.4%/33.5/41.2 HCA 2.5

This is so hard...

 

[John P]

The VG in polish is not so significant. I would want to know cut consistency, especially for #2: If there are too many individual pavilion facets > 41.2 it''s an issue (remember the PA is an average of eight unknown numbers...and so is CA). Number one is in a safer zone in broad terms, but cut consistency is still important to me. I would also want to know minor facet averages, which are not posted. Seeing Ideal-scopes for both would help in many ways.

 

[snowstorm]

Date: 12/4/2008 10:23:06 PM
Author: John Pollard
The VG in polish is not so significant. I would want to know cut consistency, especially for #2: If there are too many individual pavilion facets > 41.2 it''s an issue (remember the PA is an average of eight unknown numbers...and so is CA). Number one is in a safer zone in broad terms, but cut consistency is still important to me. I would also want to know minor facet averages, which are not posted. Seeing Ideal-scopes for both would help in many ways.

Here''s an visual picture of stone 1, don''t have any info for stone 2 though.
Some mentioned that because stone 1 is on the shallow side, it won''t look right on a ring, is that a serious issue?

 

[John P]

Date: 12/4/2008 10:35:12 PM
Author: snowstorm

Date: 12/4/2008 10:23:06 PM
Author: John Pollard
The VG in polish is not so significant. I would want to know cut consistency, especially for #2: If there are too many individual pavilion facets > 41.2 it''s an issue (remember the PA is an average of eight unknown numbers...and so is CA). Number one is in a safer zone in broad terms, but cut consistency is still important to me. I would also want to know minor facet averages, which are not posted. Seeing Ideal-scopes for both would help in many ways.

Here''s an visual picture of stone 1, don''t have any info for stone 2 though.
Some mentioned that because stone 1 is on the shallow side, it won''t look right on a ring, is that a serious issue?

There is a bit of tilt in the image but it looks like a nice stone. Complimentary minor facets. Can''t tell cut consistency but it''s certainly not bad. In my experience obstruction is not the issue some make of it with this crown/pavilion combination. It is borderline but should not be a problem.

 

[snowstorm]

Thanks for your thoughts. It is pretty nerve wreaking to buy a diamond without seeing it in person. It is no doubt the most money dense object I have, and likely will ever buy.

So in your opinion, it seems that stone 1 is a better bet than stone 2 even though it is a VG and not EX according to GIA. Can you shed some more light on what you mean by obstruction?

One more thing, how do know what the expected AGS grade for stones are? Is there an online calculator too?

 

[Garry H (Cut Nut)]

In case John has gone beddie byes, it means the stone will go dark from probably around 8 inches view distance depending on the size of your head and baseball cap as you block the available illumination.

You should read the link that someone gave you. (naughty)

 

[John P]

Date: 12/4/2008 10:55:27 PM
Author: snowstorm
Thanks for your thoughts. It is pretty nerve wreaking to buy a diamond without seeing it in person. It is no doubt the most money dense object I have, and likely will ever buy.

"Money dense" = genius term.

It is scary, but you're in the right place. You are getting input from people with high standards and the dealers here are very reputable, with strong exam/return periods and after-sale support.

So in your opinion, it seems that stone 1 is a better bet than stone 2 even though it is a VG and not EX according to GIA. Can you shed some more light on what you mean by obstruction?

The VG polish is a non-factor. Seriously. It's like having two Porsches and one has an area where the paint is slightly thinner. If someone doesn't ID which one you will never be able to tell because it's invisible. It's worth noting at the factory (lab) level, but not something the casual viewer will ever know or consider.

Obstruction is the shadow cast by the viewer (or in photos the camera). For example, the dark 'arrows' are caused by obstruction; literally they're a reflection of the dark camera lens seen in the pavilion mains of the diamond.

If the pavilion angle or pavilion/crown combo is too shallow it invites more obstruction, so more of the diamond will become darkened as the viewer gets close. This is why shallower stones are more appropriate for pendants and earrings; people get less close to them, so obstruction is less of a factor.

One more thing, how do know what the expected AGS grade for stones are? Is there an online calculator too?

Not for their light performance grade. Every diamond submitted for a DQD is judged on its own individual merits. AGS released cutting guides to manufacturers with predicted grades but they are not intended as absolute, since the diamond's individual grade will depend on several factors beyond basic 2D proportions.

 

[strmrdr]

overall the first one looks ok but personally I would look for something closer to tolk than a near 60/60.
Something along the lines of table: 54-57, pavilion: 40.6-41, crown: 34-35 with a nod towards 40.5-45.6 pavilion with a crown in the 35.5-38 and a 55-56 table in the fic range on HCA. Or a few other combos that score well on the HCA and pass the rest of the tests. (obstruction/leakage)
Once you hit 41 the shallower side 34-34.5 crown matches better and with longer lgf% being better but some will disagree with that and say the 41/35/56 with longer lgf% is fine and they can make a good case for it.
Images are close to being mandatory preferable Ideal-scope and once you get to the edges they are a must.

 

[JulieN]

The picture looks pretty good to me. Probably, it's better than I thought it would be.

 

[snowstorm]

Wow is that the Garry H of the HCA? Great site and system you have here!

Thanks John and Garry for all the info. I have learned so much from you two and the community on this site. I am really down to selecting between one of these two stones for a engagement ring. I think I am leaning towards the shallower stone GIA VG rather than the GIA EX but 2.5 HCA one. You think it is a wise choice?

John, you mentioned AGS cutting guides, do you have a link to them?

 

[John P]

Date: 12/4/2008 11:24:17 PM
Author: snowstorm
Wow is that the Garry H of the HCA? Great site and system you have here!

Thanks John and Garry for all the info. I have learned so much from you two and the community on this site. I am really down to selecting between one of these two stones for a engagement ring. I think I am leaning towards the shallower stone GIA VG rather than the GIA EX but 2.5 HCA one. You think it is a wise choice?

John, you mentioned AGS cutting guides, do you have a link to them?

They were released to the industry snowstorm; they are not published for consumers. AGS does not want them to be treated like grading charts. I do have permission from AGSL to reproduce them for educational purposes - so here's the relevant clip for stone #1. See the purple arrow I added.

As mentioned, the stone would need to go through scanning/ray-trace at AGS to know their grade decisively, since a number of additional factors must be in-line, but the indications are good.

 

[snowstorm]

Thanks for the chart John, that''s very cool.

I''ve actually ordered stone 1 this morning from the dealer, but am having 2nd thoughts as I read more about the pendant vs ring issue, I might still have a chance to cancel it but it is going to get pretty tight on timing... Thanks everyone so much for their opinion here.

Stone one has a 40.6 pavilion 33.5 crown angle, so it is in the 1 zone right at the border between 1 and 5 (I hope the GIA report didn''t rounded up for the angles here)

The purple cross hair is where I think stone 1 is at. So you going to say no to stone 2?

 

[John P]

Date: 12/4/2008 11:54:22 PM
Author: snowstorm
Thanks for the chart John, that's very cool.

I've actually ordered stone 1 this morning from the dealer, but am having 2nd thoughts as I read more about the pendant vs ring issue, I might still have a chance to cancel it but it is going to get pretty tight on timing... Thanks everyone so much for their opinion here.

Stone one has a 40.6 pavilion 33.5 crown angle, so it is in the 1 zone right at the border between 1 and 5 (I hope the GIA report didn't rounded up for the angles here)

The purple cross hair is where I think stone 1 is at. So you going to say no to stone 2?

You're welcome. I'm not saying 'no' to anything by the way. Just giving input.

If you pick nits using the chart I posted I am going to get a call from the brute squad at AGS tomorrow, angry that I'm disturbing the natives with manufacturing guides that are not intended to be applied as decisive.

Remember they are predictive 2D guidelines, for cutters considering how to plan the rough. They do not take minors, brillianteering or 3D cut consistency into account. Also remember that in addition to GIA's rounding you are looking at averages for your diamond, meaning that 8 separate numbers were averaged to determine a single crown angle and that was rounded to the nearest 0.5 degree... Pavilion and minors were averaged too.

I think the pendant vs ring issue with this combination is splitting hairs at a threshold. If you had a 40.2/33.5 combo I'd raise the red flag but this one is not likely to be of concern.

Don't take my word for this though - you will have it soon. Just as you would test drive a new car regardless of how reliable you know it is, I suggest you take this diamond on a tour-de-force when you get it. Compare it, share it, test it with the most important tools of all...your eyes.

 

[JulieN]

Well-said, John.

 

[Lorelei]

Date: 12/5/2008 12:30:36 AM
Author: John Pollard

Date: 12/4/2008 11:54:22 PM
Author: snowstorm
Thanks for the chart John, that''s very cool.

I''ve actually ordered stone 1 this morning from the dealer, but am having 2nd thoughts as I read more about the pendant vs ring issue, I might still have a chance to cancel it but it is going to get pretty tight on timing... Thanks everyone so much for their opinion here.

Stone one has a 40.6 pavilion 33.5 crown angle, so it is in the 1 zone right at the border between 1 and 5 (I hope the GIA report didn''t rounded up for the angles here)

The purple cross hair is where I think stone 1 is at. So you going to say no to stone 2?

You''re welcome. I''m not saying ''no'' to anything by the way. Just giving input.

If you pick nits using the chart I posted I am going to get a call from the brute squad at AGS tomorrow, angry that I''m disturbing the natives with manufacturing guides that are not intended to be applied as decisive.

Remember they are predictive 2D guidelines, for cutters considering how to plan the rough. They do not take minors, brillianteering or 3D cut consistency into account. Also remember that in addition to GIA''s rounding you are looking at averages for your diamond, meaning that 8 separate numbers were averaged to determine a single crown angle and that was rounded to the nearest 0.5 degree... Pavilion and minors were averaged too.

I think the pendant vs ring issue with this combination is splitting hairs at a threshold. If you had a 40.2/33.5 combo I''d raise the red flag but this one is not likely to be of concern.

Don''t take my word for this though - you will have it soon. Just as you would test drive a new car regardless of how reliable you know it is, I suggest you take this diamond on a tour-de-force when you get it. Compare it, share it, test it with the most important tools of all...your eyes.

AMEN!