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FIRE - what has more influence: Crown angle vs table size

Gemly

Rough_Rock
Joined
May 29, 2020
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83
Just trying to sharpen my understanding.

I know a smaller table tends to produce more fire. I also know a higher crown angle produces more fire. So if I’m comparing a diamond with a slightly higher crown angle vs one with a slightly smaller table, which then would produce more fire? Looking at the three sample parameters below which (theoretically) should be most firey?

Examples: Assuming all 3 have 15.5% crown height

Diamond #1
Table size: 54.5%
CA: 34.4
PA: 40.8

Diamond #2
Table size: 55%
CA: 34.5
PA: 40.7

Diamond #3
Table size: 55.5%
CA: 34.6
PA: 40.7

Thanks so much for your help! I have appts to meet with some venders in the next couple of weeks and am getting prepared.
 

LittleKite

Shiny_Rock
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May 13, 2020
Messages
102
Theoretically, a smaller table % means more area for the other facets (upper girdle, crown, star), thus more fire.
You also have to consider star%. A 55% star will give you more fire than a 50% star.
 

Serg

Ideal_Rock
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Mar 21, 2002
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2,518
Just trying to sharpen my understanding.

I know a smaller table tends to produce more fire. I also know a higher crown angle produces more fire. So if I’m comparing a diamond with a slightly higher crown angle vs one with a slightly smaller table, which then would produce more fire? Looking at the three sample parameters below which (theoretically) should be most firey?

Examples: Assuming all 3 have 15.5% crown height

Diamond #1
Table size: 54.5%
CA: 34.4
PA: 40.8

Diamond #2
Table size: 55%
CA: 34.5
PA: 40.7

Diamond #3
Table size: 55.5%
CA: 34.6
PA: 40.7

Thanks so much for your help! I have appts to meet with some venders in the next couple of weeks and am getting prepared.
These diamonds have almost identical CA and Tb. If you need a diamond with more fire you need check PA 41 CA 34.5 or even PA41.2 CA 34.5 .
 

Paul-Antwerp

Ideal_Rock
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Please allow me to use the technique of 'reductio ad absurbum'.

With all 5 angle-combinations presented already in the thread, I assure you that I can deliver you just as well a diamond with exceptional Fire as one with disappointing Fire.

That means that all following theories are flawed:
- Average proportion-sets can predict Fire.
- Smaller table produces more Fire.
- Higher crown produces more Fire.

My plea is to forget these simplifications.

Live long,
 

Gemly

Rough_Rock
Joined
May 29, 2020
Messages
83
These diamonds have almost identical CA and Tb. If you need a diamond with more fire you need check PA 41 CA 34.5 or even PA41.2 CA 34.5 .
Interesting, I’ve always read that a higher crown angle had more influence than PA (that PA basically just needs to be complimentary). A PA of 41 with a 34.5 sounds steep ...doesn’t sound complementary ...but you say that’s typically a more firey cut? Can you elaborate on why that’s so? Thank you!
 

AV_

Ideal_Rock
Joined
Aug 5, 2018
Messages
3,857
- Average proportion-sets can predict Fire.

-

... forget these simplifications.
Proportions are much more sung than precission [& I feel that the two are not-trivially related]. I cannot rememeber any one page showing just this, although ther are many, many witnesses by now.
 

daisygrl

Shiny_Rock
Joined
Dec 30, 2019
Messages
363
Theoretically, a smaller table % means more area for the other facets (upper girdle, crown, star), thus more fire.
You also have to consider star%. A 55% star will give you more fire than a 50% star.
That is not necessarily true. Larger super-ideal cut can create fire that is out of this world. Small table does not mean anything. Crowns and pavilions alignment and complementarity are much more important.
That 55%=fire is wrong as well. Most super-deals are cut to be 50-52 stars. In fact, star percentage is the last thing I would worry about when it comes to fire...or anything, really.

Or what Paul said above.
 
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Gemly

Rough_Rock
Joined
May 29, 2020
Messages
83
Please allow me to use the technique of 'reductio ad absurbum'.

With all 5 angle-combinations presented already in the thread, I assure you that I can deliver you just as well a diamond with exceptional Fire as one with disappointing Fire.

That means that all following theories are flawed:
- Average proportion-sets can predict Fire.
- Smaller table produces more Fire.
- Higher crown produces more Fire.

My plea is to forget these simplifications.

Live long,

Cut and precision are king, that’s for sure. So, theoretically if all five diamond specs listed in this thread were cut expertly, by one of the PS favorite gem cutters and you had your pick of them all, which would be your ultimate choice and why?
 
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LittleKite

Shiny_Rock
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May 13, 2020
Messages
102
That is not necessarily true. Larger super-ideal cut can create fire that is out of this world. Small table does not mean anything. Crowns and pavilions alignment and complementarity are much more important.
That 55%=fire is wrong as well. Most super-deals are cut to be 50-52 stars. In fact, star percentage is the last thing I would worry about when it comes to fire...or anything, really.

Or what Paul said above.
All the three stones listed have pavilion angles 40.7-40.8, and the question is about crown. That is why I did not comment on pavilion.
As regarding star %, I do not know where you get your info and claimed that my comments are wrong. Can you cite any article giving good reasoning? Can you comment on the impact of the length of star on the angles of lower girdles facets & star facets, to PROVE that I was wrong?
 

daisygrl

Shiny_Rock
Joined
Dec 30, 2019
Messages
363
All the three stones listed have pavilion angles 40.7-40.8, and the question is about crown. That is why I did not comment on pavilion.
As regarding star %, I do not know where you get your info and claimed that my comments are wrong. Can you cite any article giving good reasoning? Can you comment on the impact of the length of star on the angles of lower girdles facets & star facets, to PROVE that I was wrong?
You made an absolute statement, a universal, "A 55% star WILL give you more fire than a 50% star" - as if it were guaranteed. That fact alone is wrong because then the statement is prone to being reduced to absurd conclusions. Nothing about diamonds is absolute. I have seen too many "dead" stones that have 54-55% star. Check all the super-ideals for star % from HPD, Brian Gavin, WF, Victor Canera and see for yourself. Most of them are cut with a star being 50-52. Star % is the least of concerns when it comes to perfectly cut diamond.
 
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Serg

Ideal_Rock
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Mar 21, 2002
Messages
2,518
Interesting, I’ve always read that a higher crown angle had more influence than PA (that PA basically just needs to be complimentary). A PA of 41 with a 34.5 sounds steep ...doesn’t sound complementary ...but you say that’s typically a more firey cut? Can you elaborate on why that’s so? Thank you!
a diamond with big crown as P40.7Cr36 has similar ray pass as a diamond P41Cr34.5
Diamonds with deep pavilion have higher dispersion
Screenshot 2020-06-07 at 22.18.03.png

more details you can read
and
 

AV_

Ideal_Rock
Joined
Aug 5, 2018
Messages
3,857
a diamond with big crown as P40.7Cr36 has similar ray pass as a diamond P41Cr34.5
Diamonds with deep pavilion have higher dispersion
May I ask how would you show this with pictures instead of renderings?
 

Garry H (Cut Nut)

Super_Ideal_Rock
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15,308
a diamond with big crown as P40.7Cr36 has similar ray pass as a diamond P41Cr34.5
Diamonds with deep pavilion have higher dispersion
Screenshot 2020-06-07 at 22.18.03.png

more details you can read
and
Sergey I wish I could explain why this is wrong.
There are several possible reasons, but I feel them rather than know them.

1. The fire you are trying to demonstrate with deeper pavilions will not be coming from pavilion mains - most will be coming from the pavilion half facets just inside the table.

2. This is also the leakage zone in those deeper pavilion diamonds.

3. the leakage zones are dead in real life because they show the dirt on the pavilion and the light that hits them is dead and gone so can not be returned as fire (this i know from seeing close to 1 million dirty clients badly cut diamonds).

And finally as I have mentioned before - not all the rays in your demo are hitting main facets.
Take the example of your 39.8 degree pavilion angle and also aim a ray at the half facets just inside the table and rock the stone just 2 degrees and the fan is huge:

https://youtu.be/Ak4pYe_De5k
 

Serg

Ideal_Rock
Trade
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Messages
2,518
Sergey I wish I could explain why this is wrong.
There are several possible reasons, but I feel them rather than know them.

1. The fire you are trying to demonstrate with deeper pavilions will not be coming from pavilion mains - most will be coming from the pavilion half facets just inside the table.

2. This is also the leakage zone in those deeper pavilion diamonds.

3. the leakage zones are dead in real life because they show the dirt on the pavilion and the light that hits them is dead and gone so can not be returned as fire (this i know from seeing close to 1 million dirty clients badly cut diamonds).

And finally as I have mentioned before - not all the rays in your demo are hitting main facets.
Take the example of your 39.8 degree pavilion angle and also aim a ray at the half facets just inside the table and rock the stone just 2 degrees and the fan is huge:

https://youtu.be/Ak4pYe_De5k
Garry,
We have this debate 15+ years. I had started checking your "Dead Ring " theory after I saw many nice diamonds with Pavilion 41-41.2 degrees and Crown 34.5. All these diamonds had considerably more Fire and Life than diamonds with Pavilion40,7 Crown 34.5. Yes all these diamonds had been clean.
Sorry, I do not like discuss dirty diamonds. There is not any big difference in performance between the dirty diamonds with such proportions. All of them are similar ugly.
Also I do not like discuss diamond optical performance for a Cyclops.
You know very well why clean diamond P41.2 Cr34.5 have not "Dead Ring" for stereo observers .
I am developing explanations for clean diamonds and humans. And its work well for clean diamonds and humans. Anybody can organize blind test to compare P41.2Cr34.5 and P40.7 Cr34.5.
I remember you did once such test during JSK, did not you? what was a result?
It is time to fix HCA.
 

Karl_K

Ideal_Rock
Trade
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Messages
9,748
With pailion angles 41+ the lower%(lowers angle actually) makes a huge differece.
Without that information and table% and crown angle its hard to know what specificaly is being dicussed.

34.5 with 41-41.2p could range from great to blah based on table size and lowers.
 

Paul-Antwerp

Ideal_Rock
Trade
Joined
Sep 2, 2002
Messages
2,859
Please allow me to use the technique of 'reductio ad absurbum'.

With all 5 angle-combinations presented already in the thread, I assure you that I can deliver you just as well a diamond with exceptional Fire as one with disappointing Fire.

That means that all following theories are flawed:
- Average proportion-sets can predict Fire.
- Smaller table produces more Fire.
- Higher crown produces more Fire.

My plea is to forget these simplifications.

Live long,
May I simply repeat my post?

Live long,
 

yssie

Super_Ideal_Rock
Premium
Joined
Aug 14, 2009
Messages
20,689
Cut and precision are king, that’s for sure. So, theoretically if all five diamond specs listed in this thread were cut expertly, by one of the PS favorite gem cutters and you had your pick of them all, which would be your ultimate choice and why?


Ditto, thritto:
May I simply repeat my post?

Live long,
I would only add to this...

If one raises his right hand to the plane of his eyes, and then closes his right eye and moves that hand clockwise until it is no longer visible by the left eye... And repeats this in opposite for the left hand... And then opens both eyes and, say, waggles the fingers on each hand at different rates... The human brain doesn’t somehow kluge both hands into one image. It’s capable of seeing both and interpreting them as two hands moving differently.

To “maximize visible colour” means to maximize the number of dispersive fans the right pupil and the left pupil see only some portion of within a certain amount of time. So what’s more here, anyway? Is more simply “seeing colour” vs. “not seeing colour”? Is more “seeing sparks of different colours in rapid succession” vs. “slowly cycling through different colours”? Something else?

This is not a simple question. Decomposing an answer into simplistic rules is a doomed venture. Equating what the single-lens camera and stereo vision resolve is just one rathole.
 
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Garry H (Cut Nut)

Super_Ideal_Rock
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Messages
15,308
I remember you did once such test during JCK, did not you? what was a result?
It is time to fix HCA.
The test was with a Tolkowsky 'ídeal' and a shallow diamond set in earrings. Drena wore them for a week or so and they were dirty.
In various environments with friends and associates everyone preferred the shallow diamond.

However this was not relevant here because earrings and pendants are usually valued more for their brilliance and brightness than for their fire. It is hard to see the fire in pendants and earrings when they are being worn.

Sadly Sergey, you have not explained why you made these simplified ray tracing images misleading? But I don't really care. Just wish you would stop posting them as some sort of evidence.
 

Serg

Ideal_Rock
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Sadly Sergey, you have not explained why you made these simplified ray tracing images misleading? But I don't really care. Just wish you would stop posting them as some sort of evidence.
Garry,
I disagree what these ray tracing are misleading specially if you read explanations from original page. I always published it with link to full explanation. I will do same in future .
Yes these theoretical explanations disagree with your hypothesis about performance shallow and deep diamonds. You do not like it, just because it does not support your opinion.
We are cutting set MMD diamonds with range of pavilion from 40.2 to 43,2 to check our theory during blind tests. All such samples have exactly same proportions except Pavilion angle.
See "vertical line diamonds " in the attached table .


Screenshot 2020-06-10 06.28.39.png


the left sample has pavilion 40.2 when the right sample has pavilion 41.2( -/+ 0.5 degree from 40.7)
which diamond has more Fire? Brilliancy ?
Screenshot 2020-06-10 06.52.17.png
 
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Karl_K

Ideal_Rock
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9,748
Diamonds with deep pavilion have higher dispersion
It is true that pavilions on the shallow end are more directional than deeper pavilions up to a point where the deeper pavilions get more directional.
But the real driver of fire is not the mains in a mrb its the lowers.
Sure you get flashes of color off the mains but pretty much everything else is off the lowers.
 

Serg

Ideal_Rock
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It is true that pavilions on the shallow end are more directional than deeper pavilions up to a point where the deeper pavilions get more directional.
But the real driver of fire is not the mains in a mrb its the lowers.
Sure you get flashes of color off the mains but pretty much everything else is off the lowers.
main facet have very significant % of area under table even for diamonds with long halves as 80%.
I prefer to see bright with some fire main facets under table instead Dead arrows .
Yes, halves are most important facets to create Fire, but:
1) In grading reports a consumer can find only angle of main facets . So we have to give data in same coordinate system . A consumer does not anything about halves slope angle.
2) A good diamond has to have homogenise flashes distribution . A diamond with weak area under table can not be consider as a diamond with good performance. For table performance main facets are critical.
 

lovedogs

Super_Ideal_Rock
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Jul 31, 2014
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11,032
Garry,
I disagree what these ray tracing are misleading specially if you read explanations from original page. I always published it with link to full explanation. I will do same in future .
Yes these theoretical explanations disagree with your hypothesis about performance shallow and deep diamonds. You do not like it, just because it does not support your opinion.
We are cutting set MMD diamonds with range of pavilion from 40.2 to 43,2 to check our theory during blind tests. All such samples have exactly same proportions except Pavilion angle.
See "vertical line diamonds " in the attached table .


Screenshot 2020-06-10 06.28.39.png


the left sample has pavilion 40.2 when the right sample has pavilion 41.2( -/+ 0.5 degree from 40.7)
which diamond has more Fire? Brilliancy ?
Screenshot 2020-06-10 06.52.17.png
This is really interesting. Thank you for posting! Just so I understand what I'm seeing, wouldn't the one with the steep pav angle have leakage (I think thats what I see anyway). So maybe more fire/brilliance but less contrast and more leakage?
 

Serg

Ideal_Rock
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This is really interesting. Thank you for posting! Just so I understand what I'm seeing, wouldn't the one with the steep pav angle have leakage (I think thats what I see anyway). So maybe more fire/brilliance but less contrast and more leakage?
There are many types of very misleading information about leakage.
There is a myth that leakage is always bad.
There is also a myth that leakage is the worst phenomena in diamonds.

Leakage (as well as obscuration) is bad only if both eyes see leakage in the same facet simultaneously (or if facets are so small that your eyes can not distinguish them).
If one eye sees a leakage when other eye sees a flash in same facet simultaneously it creates very high binocular type contrast .
 

AV_

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@Serg What does it take to see the dark arrows of the left side diamond light up?
 

AV_

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@Serg I hereby understand that when such a stone catches a light source, it would flash me from a tilt... I cannot work out off the cuff how effective such 'catch' is, sure enough.
 

Serg

Ideal_Rock
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@Serg I hereby understand that when such a stone catches a light source, it would flash me from a tilt... I cannot work out off the cuff how effective such 'catch' is, sure enough.
@AV_
your messages are not clear enough for me.If you need my help please explain it in different way
 

OoohShiny

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There are many types of very misleading information about leakage.
There is a myth that leakage is always bad.
There is also a myth that leakage is the worst phenomena in diamonds.

Leakage (as well as obscuration) is bad only if both eyes see leakage in the same facet simultaneously (or if facets are so small that your eyes can not distinguish them).
If one eye sees a leakage when other eye sees a flash in same facet simultaneously it creates very high binocular type contrast .
Thank you for your excellent posts, Serg, and for taking the time to explain it to us 'noobs'! :)

In this situation, could we say that contrast (obstruction) and 'leakage' are interchangeable, if it means that one eye is seeing a bright flash that looks brighter due to the other eye seeing a dark/leaking facet?
 

Serg

Ideal_Rock
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Thank you for your excellent posts, Serg, and for taking the time to explain it to us 'noobs'! :)

In this situation, could we say that contrast (obstruction) and 'leakage' are interchangeable, if it means that one eye is seeing a bright flash that looks brighter due to the other eye seeing a dark/leaking facet?
@OoohShiny

Contrast is not obstruction.

Obscuration and Leakage could reduce contract as well increase contrast.
Strong (when both eyes see it simultaneously ) Obscuration /Leakage reduces contrast.
Partial (when only one eye see it ) Obscuration /Leakage increase contrast.

So it is very tricky to use these phenomena in cut design to improve optical performance
There are other phenomena also what influence to contrast
 
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