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

OoohShiny

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@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

Thank you, kind sir! :))

These things are not simple... lol
 

diagem

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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.

In order to achieve a homogeneous play-of-light visual, the precision level is of the utmost importance.
The tighter the precision on both Azimuth and slopes, the more uniformity in flash distribution. I am certain @Paul-Antwerp can elaborate on this issue more instead of repeating his post :saint: ...

I also much rather enjoy bright over obstructed arrows, the main reason me and @Rhino (Jon) altered the pavilion main angles on the AVR's when we developed them. Exactly what Sergey means.
 

diagem

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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 .

Since gemological laboratories including AGSL only consider light from above (e.g. from above girdle median), all leakage is considered a negative and is actually being educated as such!

Leakage can have quite many positives, there is a whole cutting niche partially based on a type of leakage, colored diamond face-up enhancement techniques rely on a evenly distribution of leakage areas.

What Sergey explains in the bold is much more detailed (thank you Sergey =)2) than what I simply call "partial leakage" in many instances and discussions. Most colorless fancy cuts also depend on such leakage due to their natural form/shape limitations. (A main reason for the lack of fancy cut grades)
I tried in the past to reason with the AGS laboratory leadership about the importance of spherical light existence but unfortunately it fell on deaf ears.
 

Serg

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@OoohShiny

Contrast is not obstruction.

Both Obscuration and Leakage can reduce contract as well as 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 that also contribute to contrast.

Strongest Obscuration does not disappear even at a big tilt. In Deep diamonds such obscuration has special name "Nail Head". For Pavilion Halves it happens when Pavilion slope is 43.5-44.5 For pavilion facet you see nail head if slope angle is 44.5-45.5./ Crown angle 34.5
you can see same phenomenon even in Shallow diamonds with Pavilion angle 39.5-40/ Crown angle 34.5.
"Nail Head" has not any connection with Leakage as you can find in many books
 

Gemly

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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.

I also much rather enjoy bright over obstructed arrows, the main reason me and @Rhino (Jon) altered the pavilion main angles on the AVR's when we developed them. Exactly what Sergey means.


Forgive my ignorance, but when you’re referring to dead arrows under the table and preferring bright arrows does this mean that you prefer not to see the black/dark eight armed “star pattern” in the table, but instead prefer the arms of the star to be active/white? I’ve been seeing tons of these diamonds while shopping and have passed each up immediately under the assumption that a well cut diamond will show a distinct black star on close inspection.
 

Serg

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Forgive my ignorance, but when you’re referring to dead arrows under the table and preferring bright arrows does this mean that you prefer not to see the black/dark eight armed “star pattern” in the table, but instead prefer the arms of the star to be active/white? I’ve been seeing tons of these diamonds while shopping and have passed each up immediately under the assumption that a well cut diamond will show a distinct black star on close inspection.

@Gemly @Garry H (Cut Nut) and everybody

Why is Black eight armed "star pattern" under table good for optical performance when "Dead Ring " = Leakage under table for diamonds with slightly deep Pavilions is very bad for optical performance ?
 

diamondseeker2006

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Ahhh, this reminds me of the old days! I am so glad at some point I realized that this kind of over-thinking was fruitless. I haven't seen a single superideal cut diamond that I'd refuse based on cut. Every one had fire in the right lighting. But I think it's a mistake to buy based on fire as the primary factor because the lighting needed for fire is not present as much as other lighting is unless you work in some very specific environments. Not only that, if someone lined up the stones in the original post, very few consumers could tell any difference in fire. That's the funny part about these kids of questions. If you care about best diamond performance, buy a superideal cut like CBI or ACA and you'll pretty much have excellent fire, scintillation, and light return.

I will add one comment. I did find that while I like small tables on antique cuts, I do prefer larger tables on modern rounds because they seem to be brighter overall. That's not a scientific statement, just something I have noticed visually in looking at pendant and earring diamonds.
 

Karl_K

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back to the first post.
With the same:
cutting precision
lgf%
star %
no excessive painting/digging

It would be 6 of one half dozen of another in visible fire.
 

Karl_K

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@Gemly @Garry H (Cut Nut) and everybody

Why is Black eight armed "star pattern" under table good for optical performance when "Dead Ring " = Leakage under table for diamonds with slightly deep Pavilions is very bad for optical performance ?

one looks good the other doesn't to me aka nice patterns
one has a fancy name
organised and distibuted contrast brilliance up close
obstruction gets less with distance where leakage does not.
The last one is a big one at full arm length the non-leaky diamond will be brighter if it does not have obstruction issues.
 

Gemly

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back to the first post.
With the same:
cutting precision
lgf%
star %
no excessive painting/digging

It would be 6 of one half dozen of another in visible fire.

back to the first post.
With the same:
cutting precision
lgf%
star %
no excessive p

It would be 6 of one half dozen of another in visible fire.

Thanks Karl,
You mean by “6 of one half dozen of another” that it could really go either way....a wash basically? I’m not familiar with this saying :)
 
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Serg

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one looks good the other doesn't to me aka nice patterns
one has a fancy name
organised and distibuted contrast brilliance up close
obstruction gets less with distance where leakage does not.
The last one is a big one at full arm length the non-leaky diamond will be brighter if it does not have obstruction issues.
Name is most important reason for consumers fear and behaviour.
Just changing Dead ring to Happy ring , and Black Arrows to Dead Arrows will change consumers behaviour .
 

Karl_K

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Thanks Karl,
You mean by “6 of one half dozen of another” that it could really go either way....a wash basically? I’m not familiar with this saying :)

More like they would appear very close to identical.
6=6
most likely impossible to pick apart by eye.
 

yssie

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Just changing Dead ring to Happy ring , and Black Arrows to Dead Arrows will change consumers behaviour .
There is so much truth to this.
Why are PS consumers hell-bent on seeing "arrows" in a RB and hell-bent on not seeing a "bow tie" in an oval when they stem from exactly the same phenomenon?
 

Karl_K

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There is so much truth to this.
Why are PS consumers hell-bent on seeing "arrows" in a RB and hell-bent on not seeing a "bow tie" in an oval when they stem from exactly the same phenomenon?
It is not exactly the same, one is pleasing to many people and one is not.
I find "arrows" to be pleasing as long as they behave properly and go bright when they should.
I do not like the looks of a bow tie on a oval or Marquise cut.
To me it makes them look off.
Patterns are important.
There are pleasing patterns and there are blah patterns.
Not everyone likes the same patterns but there are some that have wider appeal than others.
 

AdaBeta27

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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

...

Back in the day, PS had discussions about FIC (firey ideal cut), BIC (brilliant ideal cut), and maybe TIC (Tolkovsly ideal cut). Here's one old thread: https://www.pricescope.com/community/threads/fic-proportions.9305/ FIC generally was, at that time, a deeper stone, steeper crown angle, and very small table by modern standards. If was said to possibly have an overall "dark" (visually dark) look to it, because it favored dispersion over brilliance. I don't know whether all of that classification system was abandoned later or not. Cut science has evolved over 15-17 years.
 

Garry H (Cut Nut)

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There is so much truth to this.
Why are PS consumers hell-bent on seeing "arrows" in a RB and hell-bent on not seeing a "bow tie" in an oval when they stem from exactly the same phenomenon?

A bow tie is a consistent nail head that does not turn on-off-on-off like the very shallow RBC arrows as Sergey mentions.
 

Garry H (Cut Nut)

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Back in the day, PS had discussions about FIC (firey ideal cut), BIC (brilliant ideal cut), and maybe TIC (Tolkovsly ideal cut). Here's one old thread: https://www.pricescope.com/community/threads/fic-proportions.9305/ FIC generally was, at that time, a deeper stone, steeper crown angle, and very small table by modern standards. If was said to possibly have an overall "dark" (visually dark) look to it, because it favored dispersion over brilliance. I don't know whether all of that classification system was abandoned later or not. Cut science has evolved over 15-17 years.
There is a problem to see fire when there is a very bright white flash nearby.
This depends on diamond size and your visual acuity (and of course light size/distance/brightness).
But here is a fun game - if you are unlucky enough to need glasses - try looking at diamonds close up without - the fire you see seems to be greater :)
 

Karl_K

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But here is a fun game - if you are unlucky enough to need glasses - try looking at diamonds close up without - the fire you see seems to be greater :)
Hmmm sounds like a good reason for an upgrade, so maybe not so unlucky? :mrgreen2::mrgreen::clap::appl:
 

diagem

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A bow tie is a consistent nail head that does not turn on-off-on-off like the very shallow RBC arrows as Sergey mentions.

Sure they do, it just takes more tilt depending on the facet surface size. Also another huge issue with bow ties is the painting of the lower halves (lgf's) adjacent to the mains. If the angles are (close to) similar, both the main and the lower halves get obstructed at the same time. usually happens on shallower pavilions.

I have seen plenty of bow ties that can work very similarly to RB's
 

diagem

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There is a problem to see fire when there is a very bright white flash nearby.
This depends on diamond size and your visual acuity (and of course light size/distance/brightness).
But here is a fun game - if you are unlucky enough to need glasses - try looking at diamonds close up without - the fire you see seems to be greater :)

Also important to mention is that in diffused lighting environments, additional light which is added to the existing light already active in the diamond may overpower the play-of-light, causing the diamond to appear brighter losing the colored-flashing phenomena altogether.
 

Garry H (Cut Nut)

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Also important to mention is that in diffused lighting environments, additional light which is added to the existing light already active in the diamond may overpower the play-of-light, causing the diamond to appear brighter losing the colored-flashing phenomena altogether.

Good points in both posts Yoram :)
 

Garry H (Cut Nut)

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But here is a fun game - if you are unlucky enough to need glasses - try looking at diamonds close up without - the fire you see seems to be greater :)
Can anyone tell me why this works - try it - it really does if you are out of focus range?
 

AV_

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@Serg I am thinking of the 'black' reflections in diamonds, in the same way the 'black' finish of polished metal is thought to be a refinement: the darkness is taken as a sign that the surfaces are as bright as possible on a small object in motion; it has already been said that the characteristics of this motion [how much tilt is required to see the black turn bright & how does this turn carry through the contrast pattern of the stone] are what tells the good from the bad.
 
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AV_

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Since gemological laboratories including AGSL only consider light from above (e.g. from above girdle median), all leakage is considered a negative
...
I tried in the past to reason with the AGS laboratory leadership about the importance of spherical light existence but unfortunately it fell on deaf ears.

Even AGSL must recognize that old diamonds worked so very well in closed back settings. Do you still have the argument in writing?
 

Serg

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@Serg I am thinking of the 'black' reflections in diamonds, in the same way the 'black' finish of polished metal is thought to be a refinement: the darkness is taken as a sign that the surfaces are as bright as possible on a small object in motion; it has already been said that the characteristics of this motion [how much tilt is required to see the black turn bright & how does this turn carry through the contrast pattern of the stone] are what tells the good from the bad.

@AV_
Screenshot 2020-06-11 10.09.15.png Screenshot 2020-06-11 10.08.54.png

@Garry H (Cut Nut)
btw. Old link to the article does not work more
 
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AV_

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AV_

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@Serg 'Dynamic contrast' puts in technical terms details I feel obvious/instinctive, will read & write back.
 

Serg

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If it were a patchwork of reflections not a continuous zone, it would be part of life.

In the end page https://docs.cutwise.com/blog/sweet-line-in-round-diamonds
you can find demonstration of images in left and right eyes from different diamonds: P40.2, P40.8, P41.2

"Dead ring" from P41.2 has same Halve Pattern in each eye as black arrows from P40.8.
it creates highest positive binocular contrast and high dynamical contrast during tilting.
when all black arrows from P40.2 are visible in both eyes what creates strong negative binocular contrast, negative dynamical contrast but some positive spatial contrast .


Screenshot 2020-06-11 10.15.08.png
 
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diagem

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Even AGSL must recognize that old diamonds worked so very well in closed back settings. Do you still have the argument in writing?

Actually, my argument was that if you take that diamond out of its closed back setting it will look different (e.g. more light entering through pavilion). AGSL grades LP based on a virtual closed setting (not really closed) and doesnt take light entering from below the girdle into any consideration.

I do have the communications, I may post a few excerpts later. The communications were conducted in 2014, I dont think their system has changed since but I have not been following them much in the last years.
 
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diagem

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Even AGSL must recognize that old diamonds worked so very well in closed back settings. Do you still have the argument in writing?

These two image examples were used by me in the argument, can you notice an optical occurrence?

Star 1 Aset.png star1 technical.png
 
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