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Diamond experts: help me choose! (HCA scores 0.5, 0.7, 1.2)

GiveMePerfect

Rough_Rock
Joined
May 20, 2021
Messages
34
I don't think I can go wrong with any of these, but I want the best:
CaratsCrown AnglePavilion AngleTableDepthPavilion LengthLower girdlesStar facetsHCA
3.343440.65561.54375500.5
2.834.540.654624380500.7
3.3734.540.85861.14378501.2

If you click on the carats you should be able to see their GCAL reports.
I'm also wondering if someone can explain why the HCA scores are what they are when I thought it would be the exact opposite because of the crown/pavilion angles.
Thanks in advance!!
 

lovedogs

Super_Ideal_Rock
Premium
Joined
Jul 31, 2014
Messages
13,229
Unfortunately we aren't supposed to talk about lab diamonds here. Ask the mods to move your thread to the "MMD" subforum.
 

lovedogs

Super_Ideal_Rock
Premium
Joined
Jul 31, 2014
Messages
13,229
You should see a "report concern" button on the bottom left of your posts. I can also report it for yo. They'll move it.
 

DejaWiz

Shiny_Rock
Joined
Apr 23, 2021
Messages
143
#3 might be the best for light return, based on the many angles and proportions. Others with more understanding will have to chime in.

 
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anangel

Brilliant_Rock
Joined
Aug 1, 2008
Messages
718
Based on numbers alone, my pick is three. It also puts your diamond in the AGS Ideal category for cut.
I think the HCA is a little too forgiving with shallow crown angles, further Garry had said that diamonds with a score of less than can look dark when viewed at close inspection head one (though that is somewhat in debate). Picture below to illustrate the less than one HCA explanation.
1621603592883.png
 

DejaWiz

Shiny_Rock
Joined
Apr 23, 2021
Messages
143
This is merely what my eyes see, so your mileage may vary:


Hearts images: #1 and #2 fail because of the chevron proportions, chevron spacing, and heart tail splits.

Arrows images: #1 has 5 out of alignment, #2 has 4 out of alignment, and #3 has 3 out of alignment.

Symmetry images: #3 seems to be the best out of the bunch.

In order of best to worst, I would say 3, 1, then 2.
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
16,342
As the inventor of HCA I will explain.
All other grading systems do not give a bonus for spread or size for a given carat weight.
Most of the stones under 1.0 HCA have relatively large spreads.
Since the Tolkowsky stone has an small penalty it scores a higher number.
34.540.8

HCA should be used as a rejection tool for many reasons.

The shallowest stone there will not appeal to many shoppers when they are buying - but in my experience when being worn and viewed from normal distances they outperform, especially because they also do not show dirt as much.
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
16,342
Based on numbers alone, my pick is three. It also puts your diamond in the AGS Ideal category for cut.
I think the HCA is a little too forgiving with shallow crown angles, further Garry had said that diamonds with a score of less than can look dark when viewed at close inspection head one (though that is somewhat in debate). Picture below to illustrate the less than one HCA explanation.
1621603592883.png

798237
 

GiveMePerfect

Rough_Rock
Joined
May 20, 2021
Messages
34
As the inventor of HCA I will explain.
All other grading systems do not give a bonus for spread or size for a given carat weight.
Most of the stones under 1.0 HCA have relatively large spreads.
Since the Tolkowsky stone has an small penalty it scores a higher number.
34.540.8

HCA should be used as a rejection tool for many reasons.

The shallowest stone there will not appeal to many shoppers when they are buying - but in my experience when being worn and viewed from normal distances they outperform, especially because they also do not show dirt as much.

Thanks Garry, great to hear from you! (I've been reading lots of your posts over the weekend!)

What penalty does the 34.5/40.8 stone have? It doesn't seem like the angles are affecting the spread since the measurements are 9.62mmx9.65mm (3.37ct), while the 34/40.6 stone is 9.60mmx9.62mm (3.34ct). Unless the .03ct difference should have a greater mm difference?

Or is the large 58% table the penalty? (This is my main concern for #3, the 3.37ct.)
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
16,342
Thanks Garry, great to hear from you! (I've been reading lots of your posts over the weekend!)

What penalty does the 34.5/40.8 stone have? It doesn't seem like the angles are affecting the spread since the measurements are 9.62mmx9.65mm (3.37ct), while the 34/40.6 stone is 9.60mmx9.62mm (3.34ct). Unless the .03ct difference should have a greater mm difference?

Or is the large 58% table the penalty? (This is my main concern for #3, the 3.37ct.)

There have been a few graphical interfaces over time.
This is from one iteration in the past:
1621893901463.png
The spread penalty is around 0.45
To learn more visit the patent or for an easier read www.diamond-cut.com.au which is essentially the patent.

We dropped this because people kept striving for XXXX (which hardly exists and make no sense at all),
 

GiveMePerfect

Rough_Rock
Joined
May 20, 2021
Messages
34
Hi everyone, I narrowed it down to the 3.37 and 3.34. I was sent pics of each... can you please lmk your thoughts? The left one is the 3.37 and the right is the 3.34. Something strange and surprising I noticed is that the 3.37 appears to have more obstruction at the base of the arrows, and also less visible arrows. Am I judging this correctly?? 7950461A-1794-48D8-B7CE-706468B2D0A5.jpeg
2E4202D2-BF48-43E9-8D94-C2B481C2C1C8.jpeg
0830B9E0-0B58-452D-A762-B31DB3988FFF.jpeg
3B527247-B683-478A-B2DB-5A13A89F0F56.jpeg
 

DejaWiz

Shiny_Rock
Joined
Apr 23, 2021
Messages
143
I would go with the 3.37 since the CA and PA are complementary. I'd at least get it in my hands to that I can test drive it for a week or three and make my final determination from there.

Yes, the risk is that the 3.34 may sell while having the 3.37 in hand, but I don't think I would be disappointed with the 3.37 at all.
...this is my personal subjective opinion, so if you are leaning towards the 3.34, then don't hesitate and scoop it up!
 

PM83

Rough_Rock
Joined
Dec 23, 2019
Messages
62
I wouldn’t get too hung up over the numbers. If you can try to get both and compare in person, go with the one that you prefer visually in person!
 

GiveMePerfect

Rough_Rock
Joined
May 20, 2021
Messages
34
Unfortunately my boyfriend will not buy both for me to look at in person :roll2: He already thinks I'm crazy for not being able to pick between these two!
So all I have to go on are the reports, pics, and videos.

@DejaWiz You're not concerned about the obstruction in the 3.37?
 

DejaWiz

Shiny_Rock
Joined
Apr 23, 2021
Messages
143
Unfortunately my boyfriend will not buy both for me to look at in person :roll2: He already thinks I'm crazy for not being able to pick between these two!
So all I have to go on are the reports, pics, and videos.

@DejaWiz You're not concerned about the obstruction in the 3.37?


I'm not really seeing obstruction out of the normal realm when viewing a super ideal directly (or near directly) down at the table.

The 3.37 bears the new GCAL 8x stamp, so that's a little bit of a bonus.

My concern with BOTH is that clouds in the pavilions are notated, but they are likely very small and insignificant, given their respective higher clarity grades.
 

musicloveranthony

Shiny_Rock
Joined
Feb 1, 2014
Messages
295
Another reason I would choose the stone on the right has to do with the way I enjoy my gems and diamonds. I like to look at them a lot. I appreciate compliments from others, but I don’t buy them for their pleasure. I want a stone that’s always going to make me happy when I look at it. A stone that obstructs from head shadow would be a deal-breaker for me because I won’t get to fully appreciate it from my viewing distance. For that reason, the shallower stone on the left here wouldn’t work for me.
 
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GiveMePerfect

Rough_Rock
Joined
May 20, 2021
Messages
34
Another reason I would choose the stone on the right has to do with the way I enjoy my gems and diamonds. I like to look at them a lot. I appreciate compliments from others, but I don’t buy them for their pleasure. I want a stone that’s always going to make me happy when I look at it. A stone that obstructs from head shadow would be a deal-breaker for me because I won’t get to fully appreciate it from my viewing distance. For that reason, the shallower stone on the left here wouldn’t work for me.

When you say "shallower stone" do you mean the 3.34 or the 3.37? The 3.37 is on the left in the pics, and its total depth is a bit shallower, but the 3.34 I think is more likely to be called shallower due to the CA/PA?
 

musicloveranthony

Shiny_Rock
Joined
Feb 1, 2014
Messages
295
When you say "shallower stone" do you mean the 3.34 or the 3.37? The 3.37 is on the left in the pics, and its total depth is a bit shallower, but the 3.34 I think is more likely to be called shallower due to the CA/PA?

I mean the 3.37 that has a lower overall depth.


The stone on the right wears its proportions more attractively to my eyes
 

DejaWiz

Shiny_Rock
Joined
Apr 23, 2021
Messages
143
Be wary of the possibility that the 3.34 diamond with a CA of 34° and a PA of 40.6° may exhibit a bit of leakage and seem a bit dead after it's been set, due to the non complementing angles.

Garry explains this occurrence here:
HCA - defining ideal cut diamonds (diamond-cut.com.au)

Experienced dealers grade unset diamonds with a loupe, backlit to enable a thorough clarity examination. Well-cut diamonds appears dark and dull because the head and loupe block light from the front of the stone, while No-Go-Zone diamonds sparkle because light from the dealer’s lamp is able to enter the pavilion. This and the fact that most institutions approve diamonds with NGZ proportions explains why we find we reject more than 90% of the diamonds we see. Because less light is returned via the crown facets fire is enhanced when these stones are examined (in the manner that most dealers do) held at arms length in tweezers and rocked from side to side. The leakage area displays excellent fire, but once set of course there is no back lighting supply. This leakage not only results in a loss of light return, but also patchy static scintillation. NGZ diamonds should be set in ways that enable light to enter via the pavilion.

If it were my money and I wanted a fiery diamond, then I would try to target a 40.5-40.6° PA range with a 35.0-36.0° CA range.

Here's a chart for generalizing lighting performance based on CA and PA relationships, courtesy of Garry H (Cut Nut).

PA and CA range chart.jpg

I want you to avoid a situation where you buy the 3.34, get it delivered, and then say "Well now wait a minute - this doesn't look *anything* like the pictures and videos showed! I'm going to switch to the 3.37!"

"Sorry, it's been sold to someone else"


...and maybe I am severely overthinking this. Perhaps those in the trade can chime in and attest to what the after-set expected performance should be for a 40.6/34.0 diamond.
 
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DejaWiz

Shiny_Rock
Joined
Apr 23, 2021
Messages
143
I have a side-by-side video of the two here if everyone can give me their thoughts! 3.34 on the knuckle and 3.37 at the base.

@DejaWiz from the ASET it looks like the 34/40.6 doesn't have light leakage :mrgreen2:

That's awesome!

You can definitely tell that the 3.34 seems to have a bit of advantage with fire...so if that's what you are wanting, then snag it up!
After seeing them side-by-side in settings, I think you're going to have a real winner, regardless of which you choose. Thanks for posting that!

You can view the video at one-quarter speed and watch the magic happen in slo-mo.

Screenshot_20210603-160831.png
 
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diamondseeker2006

Super_Ideal_Rock
Premium
Joined
Jan 11, 2006
Messages
57,598
This is a tough one. By numbers alone, I would choose the 3.37. But when I look at the arrows image, the 3.34 looks more perfectly cut. It also has a a smaller table and a 15% crown, whereas the other only has 14.5%. So all in all, I think using my eyes in combination with all the numbers, I am going to chose the 3.34 E!
 
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