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What are the best numbers for 60/60?

eyvind

Rough_Rock
Joined
Sep 27, 2015
Messages
11
Hi guys,

What are the best possible numbers for 60/60 cut? What would be the main differences between best possible 60/60 cut and super ideal TIC? Is it worth to pay premium for "super ideal", if you can have a larger 60/60 for the same price? What do you think about this numbers:

1.51 ct
7.39 x 7.42 x 4.47
depth 60.4%
table 59%
CA 33.5
PA 40.8
SL 50%
LGF 75%
crown height 13.5%
pavilion depth 43%
girdle 4% medium-slightly thick
 

John P

Ideal_Rock
Trade
Joined
May 1, 2008
Messages
3,563
The charm of the 60-60, when well-cut, is abundant brightness. The nature of the cut results in less fire detected in performance as-opposed to diamonds with smaller tables and steeper crown-angles. Therefore it makes sense to try and find a configuration with robust CA-PA combinations, as well as intelligent lower-half lengths and (the point) strong cut-consistency.

The basic numbers indicated for the 1.51ct above are close to my own favorite basic 60-60 indicators* except I'd prefer the lower halves to be around 80%. YMMV.

Long and short story follow. Anyone uninterested in the nano-tech ;-) can jump to the short story...

LONG STORY: The issue with any lab report is the fact that those numbers are only indicators. There are many measurements "hidden" behind a single average. You can have two lab reports with the same table, pavilion, crown and lower half numbers but significantly different optical results.

Imagine you see two diamonds indicated as 60T 60D 40.8PA 33.5CA 50SL 80LH... Great, right?

Maybe...Maybe not.

Diamond A
60 T
60 D
40.8 PA: Actual measurements are 40.3 40.4 40.6 40.8 40.8 40.9 41.2 41.4
33.5 PA: Actual measurements are 32.9 33.0 33.2 33.3 33.5 33.5 33.8 34.0
80 LH: Actual measurements are 71 through whatever (16 total measurements on this one btw)

Diamond B
60 T
60 D
40.8 PA: Actual measurements are 40.6 40.7 40.7 40.8 40.8 40.9 41.9 41.0
33.5 PA: Actual measurements are 33.2 33.2 33.3 33.4 33.5 33.7 33.7 33.8
80 LH: Actual measurements are close to 80 (again, 16 measurements are averaged)

While the indicators are the "same," the optical properties of these two diamonds will be different.

Additionally 1: If you're looking at GIA reports, they take the indicators, above, and further round those numbers. You will never see "34.3" as a GIA Crown Angle. Every CA number is rounded to the nearest 0.5 degrees. Thus 34.3 34.4 34.5 34.6 and 34.7, although an average of 8 separate measurements, all become reported as "34.5." Same with lower halves and stars. And the pavilion angle is rounded to the nearest 0.2.

Additionally 2: As it relates to fire and scintillation: The level of cut-precision will determine how robust or broken-apart the diamond's internal reflections become. When the facets or "mirrors" are precisely aligned those internal reflections stay bigger. When the mirrors have variance and are not precisely aligned the reflections are broken apart into smaller surfaces. In a 60-60 this will have everything to do with whether you perceive fire, because larger internal reflections create wider dispersive "fans" (think of a prism) and more likelihood that your pupil will clip the fan and detect color, rather than seeing recombined (white) light, or no light at all if the internal reflections become too broken and small.

Assessing this becomes especially important in a configuration like 60-60 which can promote brightness but less dispersion is happening due to the nature of the cut. Also important in antique-transitional cuts on the other end of the scale, where the geometry promotes dispersion but overall brightness becomes the challenge.

SHORT STORY: Request an ideal-scope or ASET image. This will show where light entering the diamond is either striking the proper critical angles to return the rays back to your eyes (edge to edge brightness is the goal) or missing the critical angle and windowing on down through the pavilion (going dark in normal and soft lighting conditions). As ASET image is also helpful for getting an idea of how consistently and precisely cut the diamond is. While not a substitute for live viewing, it's far more information than averaged and rounded numbers on a lab report.
 

eyvind

Rough_Rock
Joined
Sep 27, 2015
Messages
11
John Pollard: thank you very much for finding a time to answer. I had no idea that actual measurements differ so much! This is brilliant explanation :)
Btw- in the opposition BIC-FIC is the scintillation going along with the fire? I mean, do 60-60s typically show less scintillation as well?
 

adele_h

Shiny_Rock
Joined
Sep 11, 2014
Messages
142
Chiming in with a question of my own - do 60/60 diamonds face up whiter than their Tolk counterparts (all other factors being equal) as a result of the increased white light return?
 

John P

Ideal_Rock
Trade
Joined
May 1, 2008
Messages
3,563
eyvind|1444390980|3936568 said:
John Pollard: thank you very much for finding a time to answer. I had no idea that actual measurements differ so much! This is brilliant explanation :)
Btw- in the opposition BIC-FIC is the scintillation going along with the fire? I mean, do 60-60s typically show less scintillation as well?
You're welcome. I'm glad it was clear!

Scintillation is a by-product of robust light-return and a balanced contrast pattern, coupled with movement by the diamond and/or the light source and/or the viewer.

60-60s with robust light-return and a nice contrast pattern can produce great scintillation; it just takes on a different character than a Tolk or transitional cut. This is because the typical 60-60 has longer lower-halves and a shallower crown than those others. The dispersive fans will be smaller, but if the diamond has robust angles and good cut consistency you'll see more overall scintillation events. In short, you may see less colored-flashes (smaller fans) but the character of abundant rapid flashes in performance can be just as robust in frequency and effect.
 

John P

Ideal_Rock
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adele_h|1444396225|3936581 said:
Chiming in with a question of my own - do 60/60 diamonds face up whiter than their Tolk counterparts (all other factors being equal) as a result of the increased white light return?
No. A well-cut diamond can face-up whiter than it's lab grade because the ray paths become shortened. Fine-tuned angles and 3D cut precision mean the light entering the crown is transmitted back immediately and intensely. When the light doesn't bounce around in the diamond the body color is not illuminated like it is when the diamond is viewed upside-down for color-grade assignment at the lab.

It may be interesting to know that colored gemstone and colored diamond cutting has entirely different goals for this reason. The cutter WANTS to keep light bouncing around, or passing through, to illuminate and show as much color as possible.
 

Rockdiamond

Ideal_Rock
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Messages
9,210
adele_h|1444396225|3936581 said:
Chiming in with a question of my own - do 60/60 diamonds face up whiter than their Tolk counterparts (all other factors being equal) as a result of the increased white light return?

This is a great question- and it implies that there's a standard answer- however " all other factors" are basically never equal.
Therefore if one looks at many 60/60's and many TIC/TOLK they will find examples going each way.

I have found, for example, that there are examples of comparison where the larger, slightly flatter top of a well cut 60/60 will make it look larger than a well cut tolk of exactly the same diameter.
 

John P

Ideal_Rock
Trade
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Messages
3,563
Rockdiamond|1444415738|3936706 said:
adele_h|1444396225|3936581 said:
Chiming in with a question of my own - do 60/60 diamonds face up whiter than their Tolk counterparts (all other factors being equal) as a result of the increased white light return?

This is a great question- and it implies that there's a standard answer- however " all other factors" are basically never equal.
Therefore if one looks at many 60/60's and many TIC/TOLK they will find examples going each way.

I have found, for example, that there are examples of comparison where the larger, slightly flatter top of a well cut 60/60 will make it look larger than a well cut tolk of exactly the same diameter.
David, I'm not sure I understand? A well-cut Tolk will return light edge-to-edge (see the example on the left below).
A well-cut 60-60 should do the same.

If both diamonds are "exactly the same diameter" and both return light edge to edge how can one look larger?
Unless you're talking about table-glare, which is inside the diameter and only seen in direct lighting?

Away from bright showroom lights, getting a diamond to return light edge-to-edge is all about optimizing the angles.
Regardless of 60-60, Tolk or other. So I am not sure I follow?

stone-comparison-revealed-600-pixels.jpg
 

Rockdiamond

Ideal_Rock
Trade
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Messages
9,210
comprof.jpg
Two stones of identical diameter, the one on the left 60/60, the one on the right tolk.
The 60/60 looked larger.
It might be that the more open table gives the illusion of a larger top.

My point about generalizations is that we can't make certain hard fast rules ( a tolk faces whiter, etc) because each stone has aspects that can differentiate it from another that has similar measurements.
 

John P

Ideal_Rock
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Rockdiamond|1444418806|3936737 said:
My point about generalizations is that we can't make certain hard fast rules ( a tolk faces whiter, etc) because each stone has aspects that can differentiate it from another that has similar measurements.
David, I never said a Tolk faces whiter. My answer to Adele was general, and applicable to all makes. Sorry if you read that differently. To be clear: With proper cutting 60-60 makes appear whiter face up, as do other makes. But it's not a function of smaller dispersive fans/light seen as white. It's about shorter ray paths.

Thanks for the photo. Much of the darkness in the right diamond is a reflection of the proximity of the black camera lens. The left diamond is tilted away and the mains are thinner, so they are not darkened as much.
 

Rockdiamond

Ideal_Rock
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Messages
9,210
Hi John,
Sorry for any ambiguity- I never meant to imply you said tolks face whiter as a rule.....but others surely have made such statements here, so a reader of PS might get that impression.

About the pic- I agree that the darkness in the stone on the right is caused by proximity to the camera.
That actually supports my assertion that the pic shows how it's possible for a well cut 60/60 to larger than a well cut Tolk with the same diameter. The stone on the right, being closer to the camera would look larger for that reason. But it does not.
IN real life you could easily see a difference.
 

John P

Ideal_Rock
Trade
Joined
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Messages
3,563
Rockdiamond|1444424682|3936770 said:
I never meant to imply you said tolks face whiter as a rule.....but others surely have made such statements here, so a reader of PS might get that impression.
With respect, if you're rebutting something that isn't in the thread you're posting in, you might want to provide context with a link, and then address it... Just my 2 cents. I searched every post to find who had said it and could not.

About the pic- I agree that the darkness in the stone on the right is caused by proximity to the camera.
That actually supports my assertion that the pic shows how it's possible for a well cut 60/60 to larger than a well cut Tolk with the same diameter. The stone on the right, being closer to the camera would look larger for that reason.
I fear we're not communicating well: I never said one or the other was closer. "Proximity" applies to both diamonds. However, as the RH diamond is (a) parallel with the lens and (b) has wider pavilion mains, it draws more darkness from the black lens in such a close-up situation.
 

Rockdiamond

Ideal_Rock
Trade
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Messages
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Hi John, I think we're communicating pretty durn ok:)

Point taken about proximity, and fatter pavilion mains.
Regardless, the stone on the left just looked a bit larger in real life.

I would not know how to search for the times participants here have written that cut improves color, but I can remember reading it.
There's definitely truth in the general statement, but not unqualified. Like the explanation you wrote about shorter light paths, which of course, makes perfect sense.
IN the real world of diamonds, exceptions do exist, but the principle is clear.
 

adele_h

Shiny_Rock
Joined
Sep 11, 2014
Messages
142
John and Rockdiamond,

Thank you both very much for taking the time to reply.. I started a thread asking something similar a couple of weeks ago and it slipped through unanswered, so I'm thrilled that people have taken the time to formulate a response!

Of course, I do understand that all factors are very, very rarely equal, and that no one rule will ring true on every occasion - but I certainly feel that I've gained a better understanding on why some diamonds face up whiter than others (going deeper than 'being cut well').

Thanks so much again :D
 
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