HALLOWAY CUT ADVISER

[biondorules]

Dear Friend I have a some questions regarding HCA.
I bought two stone one is the GIA cert 2161365593 3X, matching AGS cur OO1, and AGA 1B. But how is possible that using HCA the score of this beautiful stone is only 2.5??

And also regarding GIA cert 2177860435 3X, AGA 1B, how is possible that using HCA the score of this beautiful stone is only 3.7??

Please help me to understand.

 

[SirGuy]

The HCA is a rejection tool. It is used with some simple parameters to give the equivalent of a chalk outline of a stone. Your first pick is a steep/deep stone; ideally its pavilion angle should be a little more shallow with that crown angle. The second stone is a 60/60, for its big table (which isn't necessarily a bad thing).

It sounds like you've already determined they're beautiful. Did you look at them in person or look at reflector images (Ideal-Scope or ASET)? If the latter, mind posting them? If the former, your eyes are the best evaluation tool.

 

[FancyIntense]

Dear Friend I have a some questions regarding HCA.
I bought two stone one is the GIA cert 2161365593 3X, matching AGS cur OO1, and AGA 1B. But how is possible that using HCA the score of this beautiful stone is only 2.5??

And also regarding GIA cert 2177860435 3X, AGA 1B, how is possible that using HCA the score of this beautiful stone is only 3.7??

Please help me to understand.

Sometimes diamonds look beautiful on their own especially if you don't see a variety of diamonds everyday.

In a comparison it might not look as good to you.

You should go somewhere and look at high performing diamonds with great HCA scores and see if you can tell the difference.

If you paid a fair price for your stones and really like them is one thing, but if you want a high performance diamond and didn't get it you might be looking at paying more because the cut precision costs more. Unless you go down in color and clarity and up in cut precision.

An AGS score of 01 for cut is not the top cut range. But it's still pretty darn good.

Look up Good Old Gold on youtube and search for videos comparing GIA XXX stones he has a new video on lab symmetry vs optical symmetry that will explain this. Jonathon who's name is Rhino here on Pricescope makes these videos. You will love these vids!

I'm not an expert, but I have been in your shoes

 

[kenny]

Different tools, charts, and labs have different cut standards.
Unfortunately for us shoppers there is no universal agreement that "The best round cut has one bullseye."
After reading PS for 10 years, and owning a few top-cut rounds my opinion is that HCA is the tool I'd use to start the selection process.
When shopping I'd reject rounds that score over 2.0 and get an Idealscope image on those that score under 2.0.
https://www.pricescope.com/tools/ideal-scope
As already stated HCA is a rejection tool, not a selection tool.
A diamond scoring under 2.0 may still have problems ... which will be revealed by an Idealscope picture.

One reason HCA cannot identify every problem is the HCA uses averages for the CA and PA, crown and pavilion angles.
Even though the outer edge is polished into a perfect circle, every standard round has 8 sides or sections.
Each section has one CA and one PA.
If the cutter was skilled and the rough cooperated the CAs and PAs of all 8 sections can come out the same, a good thing.
On the other hand the 8 CAs and 8 PAs may vary all over the place BUT happen to average out to ideal angles, around 34.7 and 40.8.
An Idealscope image would reveal such wonkiness that the HCA could not identify.

HCA and Idealscope is a simple 2-step process that guarantees killer light peformance.
Garry Holloway, the inventor, should get the Pulitzer Prize of Diamond Shopping.

Experts with decades of experience may recognize good diamonds that this 2-step process may reject.
No problem ... you and I are not experts with decades of experience (and rounds are the most plentiful diamond shape) I highly recommend we mortals use the HCA and Idealscope.

I don't agree with, "All that matters is you love it' posts.
One, if that were the case you would not have started this thread.
Two, you may love it today under certain lightning but not all lighting, or learn more about cut and finally witness TOP TOP light performance in the future.

The above hopefully answers your questions but now for your dilemma, what to do with diamonds you already bought now that you found out they score over 2.0.
While they are probably not TOP TOP cut, they are likely quite well cut compared to what else is out there.
Selling diamonds makes money go poof, unless you bought them from a vendor with a good trade-up policy.

Is it worth the cost to get better cut? Only you can say.
Does TOP TOP cut even look better enough to justify the upgrade cost? Only you can say.
Are you the type of person who simply MUST have the best cut regardless of cost and maybe going down in size, color, or clarity? Only you can say.

If I were you I'd buy a super top-cut round from one of the reputable PS vendors like Whiteflash, Good Old Gold, James Allen, Wink Jones.
Compare it to your diamonds for several days in all kinds of lighting.
If you think it's not worth it return it within the return period for a full refund, minus shipping.
I don't know your budget but it will probably cost under $100 in shipping to put this subject to rest.

 

[MelisendeDiamonds]

Double post.

 

[MelisendeDiamonds]

Dear Friend I have a some questions regarding HCA.
I bought two stone one is the GIA cert 2161365593 3X, matching AGS cur OO1, and AGA 1B. But how is possible that using HCA the score of this beautiful stone is only 2.5??

And also regarding GIA cert 2177860435 3X, AGA 1B, how is possible that using HCA the score of this beautiful stone is only 3.7??

Please help me to understand.

What does matching AGS cur 001 mean?
Yes there is a bullseye range that hits the top grade on all 4 tools, the two diamonds you posted certainly do not.

Whether this matters to you is subjective and quite another topic.

But since you did not give the carat weight noone could even look up the report numbers you posted.

 

[kenny]

Yes there is a bullseye range that hits the top grade on all 4 tools, the two diamonds you posted certainly do not.

I do not dipute this.
I used the round bullseye graphic because it does a good job of illustrating common but incorrect thinking on cut.
Not all tools/labs/charts agree, match or track, or line up around a common center, as with a round bullseye.

For instance see this HCA's graphic.
Besides an X where the diamond falls it also shows the crown and pavilion angle ranges for AGS and GIA's top cut grades when a diamond has, in this case, a 57% table.

AGS's top cut range is the solid white line and GIA's is the dotted line.
They are quite different and this shows how loosey-goosey GIA's top cut grade of Excellent is compared to AGS's top grade they call Ideal.
Some diamonds could make the top grade of one lab but not the other.

AGS and GIA's ranges do not have a common center!

Also, very significantly, note that AGS's range is not fully surrounded by GIA's range.
Hence the argument cut grading it is not a bulls-eye, set-subset kind of thing with a universally agreed to center point.

 

[biondorules]

Means that the 0.62ct D IF 3X N GIA cert 2161365593 match with AGS OO1
Cr depth 15% angle 35 - Pav. depth 43.5% angle 41 - Tab% 58
0 0 1

Average Crown Depth/Angle
% Depth Angle AGS Cut Grade

13.5 13.7 31.7 32.1 3
13.8 13.9 32.2 32.6 2
13.9 14.5 32.7 33.6 1
14.6 15.7 33.7 35.8 0
15.8 16.0 35.9 36.3 1
16.1 16.3 36.4 36.8 2
16.4 16.6 36.9 37.3 3

Average Pavilion Depth/Angle
% Depth Angle AGS Cut Grade

41.2 41.6 39.5 39.8 4
41.7 42.1 39.9 40.1 2
42.2 43.8 40.2 41.2 0
43.9 44.3 41.3 41.5 1
44.4 44.8 41.6 41.8 2
44.9 45.3 41.9 42.2 4

Average Table Diameter %
% Diameter AGS Cut Grade


50.4 51.3 3
51.4 52.3 1
52.4 57.5 0
57.6 59.5 1
59.6 62.0 2
62.1 63.5 3

Regarding the 0.52ct D IF 3X N GIA cert 2177860435
Tab 60%-Tot depth 60.8% - Cr angle 34 - Cr depth 13.5 % - Girdle 3.5% - Pav angle 41.2° - Pav. 43.5%
Metching with the following parameters

Class I American/Tolkowsky Cut
• Tab% : 53–60%
• Tot depth: 59.3–61%
• Cr angle 34–35 °
• Cr depth: 13.5–16.2%
• Girdle 0.7–3.5% Thin to sl thik
• Pav angle: 40.20–41.20°
• Pav: 42.52–43.57%

Am I right or not? or maybe I did not understand something?
They have been my first buying

 

[biondorules]

Thanks for all reply.

 

[MelisendeDiamonds]

Yes there is a bullseye range that hits the top grade on all 4 tools, the two diamonds you posted certainly do not.

I do not dipute this.
I used the round bullseye graphic because it does a good job of illustrating common but incorrect thinking on cut.
Not all tools/labs/charts agree, match or track, or line up around a common center, as with a round bullseye.

For instance see this HCA's graphic.
Besides an X where the diamond falls it also shows the crown and pavilion angle ranges for AGS and GIA's top cut grades when a diamond has, in this case, a 57% table.

AGS's top cut range is the solid white line and GIA's is the dotted line.
They are quite different and this shows how loosey-goosey GIA's top cut grade of Excellent is compared to AGS's top grade they call Ideal.
Some diamonds could make the top grade of one lab but not the other.

AGS and GIA's ranges do not have a common center!

Also, very significantly, note that AGS's range is not fully surrounded by GIA's range.
Hence the argument cut grading it is not a bulls-eye, set-subset kind of thing with a universally agreed to center point.

Kenny,

The GIAL and AGSL top grades have excellent overlap although AGSL is more selective and has tighter tolerances for its top grade.
Stick with the combos where both labs agree and avoid the borders and a safe choice will usually be made.

They two labs more common ground than disparity as to be expected, they share family members in high positions in both organizations. Since CA/PA are dependant on one another one would not expect a circular plot like a dart board.

Where they disagree: GIAL includes more steep deep combinations. AGSL has potentially included some combinations with shallow pavilion angles(40.4, 40.6) and steep crown angles(36 - 37) that might get AGSPGS of 0 (remember it is actually ray tracing not averaged numbers) for cut if everything else was near perfect(symmetry, correct choice of LGFs, girdle etc) but GIA would not give it Excellent. These borderline combos often fail the raytracing test and even if they do are best worth avoiding anyway.

 

[MelisendeDiamonds]

Means that the 0.62ct D IF 3X N GIA cert 2161365593 match with AGS OO1
Cr depth 15% angle 35 - Pav. depth 43.5% angle 41 - Tab% 58

AGSL cut grades each round diamond based on an accurate scan of each facet and then using ray tracing. Do not consult charts or numbers to try to simulate AGSL grading you cannot account for minor facets and they don't use averaged numbers like GIA grading does.

While 58%t and 35/41 CA/PA would get AGS 0 with perfect symmetry you cannot be sure due to the averaging.

D IF is very rare and carries a huge premium, for the same money you could have a 0.9 carat G SI1 with excellent proven cut.

 

[Texas Leaguer]

Yes there is a bullseye range that hits the top grade on all 4 tools, the two diamonds you posted certainly do not.

I do not dipute this.
I used the round bullseye graphic because it does a good job of illustrating common but incorrect thinking on cut.
Not all tools/labs/charts agree, match or track, or line up around a common center, as with a round bullseye.

For instance see this HCA's graphic.
Besides an X where the diamond falls it also shows the crown and pavilion angle ranges for AGS and GIA's top cut grades when a diamond has, in this case, a 57% table.

AGS's top cut range is the solid white line and GIA's is the dotted line.
They are quite different and this shows how loosey-goosey GIA's top cut grade of Excellent is compared to AGS's top grade they call Ideal.
Some diamonds could make the top grade of one lab but not the other.

AGS and GIA's ranges do not have a common center!

Also, very significantly, note that AGS's range is not fully surrounded by GIA's range.
Hence the argument cut grading it is not a bulls-eye, set-subset kind of thing with a universally agreed to center point.

Kenny,

The GIAL and AGSL top grades have excellent overlap although AGSL is more selective and has tighter tolerances for its top grade.
Stick with the combos where both labs agree and avoid the borders and a safe choice will usually be made.

They two labs more common ground than disparity as to be expected, they share family members in high positions in both organizations. Since CA/PA are dependant on one another one would not expect a circular plot like a dart board.

Where they disagree: GIAL includes more steep deep combinations. AGSL has potentially included some combinations with shallow pavilion angles(40.4, 40.6) and steep crown angles(36 - 37) that might get AGSPGS of 0 (remember it is actually ray tracing not averaged numbers) for cut if everything else was near perfect(symmetry, correct choice of LGFs, girdle etc) but GIA would not give it Excellent. These borderline combos often fail the raytracing test and even if they do are best worth avoiding anyway.

Good stuff guys. I would just emphasize the point made in the last paragraph. The AGS system is not based upon look-up tables and averaged and rounded measurements(such as GIA system or HCA tool). It is based upon ray tracing a very accurate model of the diamond and factoring in the contribution of every facet to the overall light performance of the diamond.

I agree with the assessment that while GIA is loose relative to AGS, and the charts show that pretty clearly, you can't take the numbers from a GIA cert and predict with certainty how a diamond will perform in actual ray tracing analysis.

 

[Texas Leaguer]

Means that the 0.62ct D IF 3X N GIA cert 2161365593 match with AGS OO1
Cr depth 15% angle 35 - Pav. depth 43.5% angle 41 - Tab% 58

AGSL cut grades each round diamond based on an accurate scan of each facet and then using ray tracing. Do not consult charts or numbers to try to simulate AGSL grading you cannot account for minor facets and they don't use averaged numbers like GIA grading does.

While 58%t and 35/41 CA/PA would get AGS 0 with perfect symmetry you cannot be sure due to the averaging.

D IF is very rare and carries a huge premium, for the same money you could have a 0.9 carat G SI1 with excellent proven cut.

+1

We were posting at the same time.

 

[biondorules]

Thanks a lot for your suggestion.

Anyway I cannot understand how have some diamonds cut VG with an HCA score less than 2 and how can be 3X cut with HCA score more than 2?

 

[kenny]

Thanks a lot for your suggestion.

Anyway I cannot understand how have some diamonds cut VG with an HCA score less than 2 and how can be 3X cut with HCA score more than 2?

... different opinions on what proportions result in the best light performance.

You are assuming light performance is as straightforward as carat weight, which would be the same on anyone's scale.

 

[MelisendeDiamonds]

Thanks a lot for your suggestion.

Anyway I cannot understand how have some diamonds cut VG with an HCA score less than 2 and how can be 3X cut with HCA score more than 2?

Show us an example of HCA <2 and GIA Very Good for cut and I will tell you why the difference for that particular example. While the situation is rare there are some combos where the two methods differ in their conclusions. In most cases those are not worth selecting if you can't see the diamond before purchase but it still might be educational to explore.

 

[biondorules]

The following stone is 0.5ct D IF VG VG G N GIA Cert 2146123614 found in pricescope
Show AGA 1B and HCA score 1.4

My stone is 0.52ct D IF 3X N GIA Cert 2177860435 That I payed not cheap!
Show AGA 1B and HCA score 3.7


Which is the better stone?

 

[MelisendeDiamonds]

The following stone is 0.5ct D IF VG VG G N GIA Cert 2146123614 found in pricescope
Show AGA 1B and HCA score 1.4

My stone is 0.52ct D IF 3X N GIA Cert 2177860435 That I payed not cheap!
Show AGA 1B and HCA score 3.7


Which is the better stone?

Well first I should reiterate that you are giving up a lot of size to get the top color and clarity grade. Most people might not be able to tell the difference between a G and D unless the two were side by side. Anything eye clean to the wearer would be seen as the same as an IF stone as well. But thats a choice you made and are aware of now.

The top stone

http://www.gia.edu/cs/Satellite?rep...ename=GIA/Dispatcher&c=Page&cid=1355954554547

The averaged angles are fine but it did not get top grade due to its symmetry and polish issues. These are red flags and may indicate craftmanship issues or problems with the surface of the rough. There is also an extra facet which may or may not impact brilliance.

Your stone has a deep pavilion 41.2 it might be fine with a crown of 34 but it likely has less life under the table than other more optimal combinations. No way to tell without images.

 

[biondorules]

I understand an i am agree with your position, but I can not understand how a cut VG VG G got a core less than 2 by HCA and AGA 1B

And my stone 3X only 3.7 by HCA and also 1B by AGA

That I cannot understand .

Color and clarity are my choose

 

[luvdajules]

Well the HCA is a calculated number based off of 4 averaged measurements (table, depth, CA, PA). Whereas the VG VG G include polish and symmetry values. So, you are saying that a VG cut has a HCA of under 2 whereas your triple X has a 3.7? I can believe your triple X has a 3.7 HCA score as we all know GIA triple X is over broad, but it still can be pretty in many lighting conditions. My newbie guess is that the other stone you are referring to has complimentary angles but suffered from a rule that the cut grade can't exceed the other two grades or something or other. That's my story and I'm sticking to it unless someone can enlighten us further, lol.

 

[biondorules]

Thanks to all, I am thinking that sometime you pay more money for 3x GIA for nothing, GIA 3VG and GIA 3X can have the same performance! or can have better performance the VG instead the 3X.
For me is incredible

 

[SirGuy]

The "very good" stone has an extra facet and some polishing issues. It could also simply not be cut as well on top of that. Please remember that the HCA is a rough estimator and is used for simple and quick rejection when looking at a lot of stones. It's not meant to be an end-all grade of a stone's performance. A lower score just means it's worth closer consideration. It's not a perfect thing; there will be some stones above 2 that would have been worth a further look, and some below 2 that you'd reject after looking at images.

 

[MelisendeDiamonds]

My newbie guess is that the other stone you are referring to has complimentary angles but suffered from a rule that the cut grade can't exceed the other two grades or something or other. That's my story and I'm sticking to it unless someone can enlighten us further, lol.

In order for GIA to assign a cut grade of Excellent both polish and symmetry must be Very Good or Excellent.
http://diamondcut.gia.edu/pdf/polish_and_symmetry.pdf

 

[Texas Leaguer]

My newbie guess is that the other stone you are referring to has complimentary angles but suffered from a rule that the cut grade can't exceed the other two grades or something or other. That's my story and I'm sticking to it unless someone can enlighten us further, lol.

In order for GIA to assign a cut grade of Excellent both polish and symmetry must be Very Good or Excellent.
http://diamondcut.gia.edu/pdf/polish_and_symmetry.pdf

To state this another way, the GIA system will not allow an overall cut grade to be more than one grade higher than either polish or symmetry, irregardless of how good the table/crown/pavilion angle combination is.

Not only do the GIA tables and HCA tables differ in terms of underlying assumptions about table/crown/pavilion measurements and their effect on performance, the HCA score does not take into account polish and symmetry, nor does it factor in the contribution of star, upper and lower girdle facets. This is a statement from the landing page of the HCA tool:

HCA gets no info on symmetry, polish and minor facets; use it only to reject likely bad performing diamonds to narrow down your final selection. Ideal-Scope images and independent appraisers can help after that.

If you run the numbers on the GIA Facetware tool, and use VG VG for polish and symmetry grades, the overall cut grade is Ex. Therefore, it is the symmetry grade that knocks down the overall cut grade on this stone. And this might be related to the extra facet.

 

[Garry H (Cut Nut)]

The following stone is 0.5ct D IF VG VG G N GIA Cert 2146123614 found in pricescope
Show AGA 1B and HCA score 1.4

My stone is 0.52ct D IF 3X N GIA Cert 2177860435 That I payed not cheap!
Show AGA 1B and HCA score 3.7


Which is the better stone?

the half carat stone has been dropped from GIA Ex because the symmetry is graded as Good. in the other aspects the proportions are great. The polish is VG which is rarely an issue in life and brilliance.
I have seen H&A's with Good GIA symmetry - so you would not reject such a stone without seeing it.
i dont have time to check your other stone (post proportions please), but that proportion set for the 0.50ct is a firey stone with great everything but a slightly smaller spread.
But if the good symmetry means a real drop in symmetry then this stone will have weak zones - but often the issue is a tilted table which incorrectly throws crown and pavilion angles way off. A whole complex topic.

 

[Texas Leaguer]

Thanks to all, I am thinking that sometime you pay more money for 3x GIA for nothing, GIA 3VG and GIA 3X can have the same performance! or can have better performance the VG instead the 3X.
For me is incredible

Just to be clear, it is entirely logical that the GIA system assumes that overall performance can be negatively effected by more than one grade deduction in either polish or symmetry.