Confused - GIA Excellent but bad HCA - Advice Please

[sktung]

First, I am very thankful to have found this site. It has provided a wealth of knowledge and information but it has also created some confusion that I am hoping the experts here can help me resolve.

I have been looking at a Round Brilliant Diamond with the following specs:

Measurements: 7.61 - 7.66 x 4.79 mm
Carat Weight: 1.71
Color Grade: F
Clarity Grade: SI1

Proportions:
Depth: 62.7 %
Table: 55 %
Girdle: Medium to Thick, Faceted
Culet: None

Finish:
Polish: Good
Symmetry: Very Good
Fluorescence: None

Additional Information
Crown Angle: 31.5°
Crown Height: 14 %
Pavilion Angle: 41.8°
Pavilion Depth: 44.5 %
Star length: 55 %
Lower Half: 80 %

Cut Grade: Very Good

Comments: Additional clouds are not shown.

All of the additional information is not on the actual physical GIA report, but it is on their electronic online report at GIA.EDU. I called GIA and they verified that the information should be accurate and I am working under that assumption.

According to the GIA Facetware estimator, the cut should be EXCELLENT but according to their own report it is Very Good. This is not that big a concern to me.

However, plugging the numbers into the HCA, I come back with a score of 3.9! This definitely gives me concern.

Having examined the stone personally through a loupe, it is one of the CLEANEST SI1 stones I have ever seen and the price is very competitive.

Bottom Line - should I pass on this stone and keep looking?

Any advice would be GREATLY appreciated!

Thanks,
Stephen

 

[strmrdr]

https://www.pricescope.com/community/threads/gia-ex-let-the-buyer-beware.41371/

its a steep/deep

 

[Small]

Pass...like strm said...it''s a steep/deep!

 

[sktung]

Thanks for the prompt responses!

So if I am understanding this correctly. GIA guidelines rate this stone as a VG or EX cut but in reality I am paying for a lot of weight that is not visible?

Setting this aside, should the HCA score be a greater concern? Are there any other specifications of the stone that I should be concerned with?

Once again, I humbly await the input of those who have greater experience/knowledge...

Thanks.

 

[Garry H (Cut Nut)]

I am considering the "two eyes effect" and relaxing HCA so that around 2.5 would be excellent in steeper deeper stones.
But there is no way you should buy that stone.

 

[Small]

So if I am understanding this correctly. GIA guidelines rate this stone as a VG or EX cut but in reality I am paying for a lot of weight that is not visible?

Setting this aside, should the HCA score be a greater concern? Are there any other specifications of the stone that I should be concerned with?


I''m definitely no expert. I just started posting a few weeks ago but have been learning and lurking for some time now. Yes, you are paying for weight that isn''t visible thus the deep comment. And the crown angle

What is it you are wanting in your diamond? Are you looking for large size along with great performance?

Ok...so here is something for instane that is going to be a better performer...like I asked above...not sure what you are looking for and have no idea the price range so I''m just throwing something out there that rates well on the HCA.

http://www.whiteflash.com/diamonds/diamond_Details.aspx?itemcode=AGS-6868309

Ok...so notice the dimensions on this 1.66 stone...the measurements 7.69-7.71 are bigger than your 1.71...see how the deepness of the stone carries weight that you can''t see. Also the crown angle is in the preferred 34 range.
Rates 1.5 on the HCA

This is just an example of the difference. I used ''pricescope my diamond'' and put in some specs to see what I could find. It''s a great tool and especially you can compare. I would definitely come down in size and get a great cut diamond. I personally just purchased a .926 Infinity cut diamond from Wink. While I really wanted a 1ct plus I was most concerned about cut for my money. So I went a bit smaller and am getting a stellar looking diamond that scores 1.2 on HCA...I don''t think I''ll be disappointed!
Good luck. Hope this example helps a bit.

 

[strmrdr]

After my nap it looks like I misread the specs as 35.1/41.8 not 31.5/41.8
which would make it a shallow/too deep.
The effect is the same light leakage and it is small for its weight.
There are a lot better combos out there.

I like to stick in the hca 1-2 range myself.

 

[Dancing Fire]

Date: 3/9/2006 11:54:19 PM
Author: sktung
Thanks for the prompt responses!

So if I am understanding this correctly. GIA guidelines rate this stone as a VG or EX cut but in reality I am paying for a lot of weight that is not visible?

Setting this aside, should the HCA score be a greater concern? Are there any other specifications of the stone that I should be concerned with?

Once again, I humbly await the input of those who have greater experience/knowledge...

Thanks.

HCA do not like pavil angle over 41'.your best bet would be 34.3-34.7' crown X 40.7-40.8' pavil.

 

[Garry H (Cut Nut)]

Date: 3/10/2006 2:08:23 AM
Author: Dancing Fire
HCA do not like pavil angle over 41''.your best bet would be 34.3-34.7'' crown X 40.7-40.8'' pavil.

DF HCA will give great scores for diamoinds with all the way up to 42 degrees pavilion angles - but the crown angles must be very shallow - below 30 degrees and then it will only accept slightly thick + gridles or it will warn you that there is a risk of chipping. (the girdle thickness is calculated by subtraction of crown height and pavilion depth from the total depth)

 

[valeria101]

Date: 3/10/2006 12:39:30 AM
Author: Garry H (Cut Nut)
I am considering the ''two eyes effect'' and relaxing HCA so that around 2.5 would be excellent in steeper deeper stones.
But there is no way you should buy that stone.

...... so that at least some GIA Ex out there pass the test?

There are quite a few new GIA certs out there now. I wonder if indeed most are on the heavy side, or it makes some sense to look for cherry HCA scores among the new picking with proportions on the report. Did anyone make a count?


Btw.
This, leaving the rounding bit aside - that would mean taking a wider shot on the HCA chart - with a small rage of scores that can easily be all good or all bad. Easy enough.

 

[sktung]

The consensus appears to be take a pass on this stone.

So I have been playing around with searching by cut and have come up with the following stone:

http://www.jamesallen.com/diamond.asp?item=315333

Any thoughts? Should this be eye-clean?

Although a little out of my price range, these other two stones appeared promising:

http://www.whiteflash.com/diamonds/diamond_Details.aspx?itemcode=AGS-3098102#
http://www.jamesallen.com/diamond.asp?cid=131&item=315332

Are there any clear advantages for these two stones that make the extra budget stretch worthwhile?

James Allen appears to be a respected vendor on this forum.

My quantifiable requirements are D-F Color and no lower than a clean SI1 for a stone 1.50-1.75 carats. I realize the sweet spot appears to be G SI1 but I am very firm on the color requirement.

Once again - I appreciate any input/insight. This is a purchase where I definitely want as much information as possible

- Stephen

 

[JulieN]

Date: 3/10/2006 5:20:18 AM
Author: sktung
http://www.jamesallen.com/diamond.asp?item=315333

Any thoughts? Should this be eye-clean?

-I wouldn''t call this one a super-ideal (the IS shows it''s a little wonky) but it still looks nice, and it looks really eye-clean to me.

Although a little out of my price range, these other two stones appeared promising:

http://www.whiteflash.com/diamonds/diamond_Details.aspx?itemcode=AGS-3098102#
-Nice. Not perfect, but very nice.
http://www.jamesallen.com/diamond.asp?cid=131&item=315332
-Pass.

James Allen appears to be a respected vendor on this forum.
-Yes

 

[valeria101]

That E-SI1 looks stupendous - colorless, clean and top cut by all the tests and gauges applied to it.

I don''t know how (or why?) to hunt to least bit of H&A perfection. If there is some difference between the technical extreme achievable and this... I wonder if I could see it. As for paying for it... up to you.

My 2c




Btw. Re. the tilt in the IS image.

It shows here too, but I don''t know what it is (miss-alignment of the stone relative to the camera of 1-2 degrees, or slant of the table versus the girdle plane of the stone). If the second is true, I wonder what''s up with that anyway, since the IdealScope picture does show the right colors, so to speak. The description doesn''t contain anything about grading H&A, so I don''t feel good about second guessing the IS image for that.

Since H&A doesn''t relate strictly to brilliance (you can get the pattern while there''s quite a bit of leakage from steep - deep angles and what not), I leave it up to you to consider the romantic appeal and premium attached to it.

 

[valeria101]

'Sktung' ... this post is a bit off the trail of your post. I hope you do not mind.

None of the diamonds in your last post enter in the range of proportions talked about below (crown 31-32 degrees, pavilion 41-41degrees) and I doubt there would be many chums like that either listed among the cherry pickings by Pricescope sellers or anywhere on the Net with proportions given.

I only wanted to get a bit more into Garry's suggestion about extreme crown/pavilion combinations. And Strm critique.

Date: 3/10/2006 1:46:18 AM
Author: strmrdr

31.5/41.8 which would make it a shallow/too deep.

The effect is the same light leakage and it is small for its weight.

There are a lot better combos out there.

Got a question or two Re. 'same light leakage'

What is 'shallow - too deep' ? If I am not mistakin' there is a trade-off between crown and pavilion angles, which would mean shallow & deep combinations should fly.

Now, there is a penalty for angles below 30 and over 40 on GIA reports.

This may be wrong in some way, but...

.... I always assumed this has something to do with durability (the shallow angles get the girdle brittle, the steep ones the edge of the table - or something like that). But there seem to be 'right' combinations of pavilion angles towards either end. Guess there's no secret by now which extremes may be more on my taste, but in fact, I don't discriminate either. Beyond those two extremes, things happen too, but it sounds like the story gets complicated with considerations of contrast and what not.

Please note that this statement is lined up for consideration.




Here's why I don't understand your statement all that well

It looks like 31-32 crown / 41-42 pavilion don't look all that bad, get AGS1 on the new scale with a small hit for contrast, while brilliance turns out a hair split better than the bulls-eye of everyone's ideals (the usual tradeoff...). Took the liberty to adjust table and minors for every combination of angles in that range - 'best' turns around 60% table and 55% - 80%.

At least spread is clearly at least as good (6.5-6.5mm) as any. If this is small for the weight, so is every AGS0, H&A super-duper ideal.

Now, I've got this distinct feeling of walking a thin line here - playing around with grown-up toys.

 

[strmrdr]

http://www.jamesallen.com/diamond.asp?item=315333

Angles just make the cut over being too shallow/shallow looks like a nice near h&a diamond.
Jim or Josh can tell you of its eyeclean.

http://www.whiteflash.com/diamonds/diamond_Details.aspx?itemcode=AGS-3098102#
WF ACA some of the top diamonds out there.

http://www.jamesallen.com/diamond.asp?cid=131&item=315332
Pricey compared to the other 2.
Angles on the near steep/deep side with a little leakage in the IS.
The other 2 if they are eyeclean are better values but this one isnt that bad.

Either of the first 2 would be my pick if they are eyeclean, the first sounds like it fits your budget better.

 

[strmrdr]

Ana,
I like shallow/deepish ie 33-34/low 41.x diamonds they can be very very bright diamonds.
The hca does a good job of sorting out the good and bad ones.
Hca says this ones combo dont work well.
This one takes it too far and gets little contrast and leakage under the table.
at 62.7 % depth its going to face up smaller than most super-ideals in the 60.6 to 62 range.

The bottom edge of the black line is ~41.8 there isnt much red there to hit

 

[valeria101]

Sorry I lost track o this thread...

I think we are talking about different things. I chose angles first and optimizing table for that improves both light return and spread. The respective table fit to the flatter crown is at least 60. With smaller tables things look pretty bad, as you say.

Not sure, but I suspect that the ''scintillation'' metric in the HCA related to the ''contrast'' in the DiamCalc''s language. And it is apparent there what does get lost. I would see this as a bonus on half carat and below, and a pretty bad thing above 3 cts...

Here''s what I was talking about: