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Blog Guess What? Dispersion And Fire Aren't The Same Thing

bcmacdonald

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Diamond dispersion is NOT FIRE. Click for a hot explanation with illustrations - and learn why you may want WINDOW SEATS on a plane.

2021-05-fire-dispersion-featured-image-1-e1623700949832-1024x573.jpg


John Pollard published a new blog post.
Really?

Yes, really. If you love gemstones you'll want to know the difference.

May I ask why?

<img class="aligncenter wp-image-118930"...

Continue reading the Original Blog Post.
 
Last edited:

Karl_K

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Excellent article sir John!!!
Lets get double down geeky for a second.
"Diamond experts have known for a long time that high crowns and small tables (like antique diamonds) promote more visible fire"

Depends on the lighting, what is really does is shift the lighting that is capable of producing fire in the diamond.

In strong multiple small direct light source lighting that is highly conductive to fire a stone with an aircraft carrier table could show more fire but that might be the only lighting it will show fire under.
 

DejaWiz

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Great article! I will admit that I am guilty of interchanging the two terms when describing lighting performance to people that aren't well versed on diamond cut quality and light performance.
 

John Pollard

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Excellent article sir John!!!
Lets get double down geeky for a second.
"Diamond experts have known for a long time that high crowns and small tables (like antique diamonds) promote more visible fire"

Depends on the lighting, what is really does is shift the lighting that is capable of producing fire in the diamond.

In strong multiple small direct light source lighting that is highly conductive to fire a stone with an aircraft carrier table could show more fire but that might be the only lighting it will show fire under.
Thank you Karl. True enough about the AC table and lighting. On that note, if you can find me an AC sized diamond, I could have it fashioned into the most awesome Nimitz-sized emerald cut ever. I feel that would be more puritanical than sawing it into a pair of destroyer-sized super-performers.

The high crown comment was a nod to physics. Light on an efficient path in/out of a diamond with X-Y Table-PA and 15% crown height will separate more than light passing through the same XY with only 5% crown height, because light exiting the 15% crown has passed through more diamond material.

There's also a matter of optimizing compound mirror size/integrity through a range of tilt, but that's a horse of a different spectral color. :cool2:
 

yssie

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This. Is. Awesome.

Never met an engaging optics article before.

Nailed it!!!!
:bigsmile:
 

Starstruck8

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Light on an efficient path in/out of a diamond with X-Y Table-PA and 15% crown height will separate more than light passing through the same XY with only 5% crown height, because light exiting the 15% crown has passed through more diamond material.

This is part of the story, but is there is more to it? Suppose you are looking straight on to a stone, and you get a flash from a crown facet (other than the table). The angle of incidence of the light exiting the stone will be greater for a steeper crown. This will result in greater angular spread of the fan leaving the stone, hence greater width of the fan at your eye. I suspect that this effect is at least as important as greater path length inside the stone.
 

Garry H (Cut Nut)

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This is part of the story, but is there is more to it? Suppose you are looking straight on to a stone, and you get a flash from a crown facet (other than the table). The angle of incidence of the light exiting the stone will be greater for a steeper crown. This will result in greater angular spread of the fan leaving the stone, hence greater width of the fan at your eye. I suspect that this effect is at least as important as greater path length inside the stone.

Yes and no.
Yes if you are close up to the diamond.
No if you are a long way away as the intensity of the flash will be too dim to notice.
 

Karl_K

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I once sat down and started listing all the variables that will effect if you will see fire.
I stopped at 120+ because I got bored and it was going to take hours to list them all because it was just getting started.
 

diagem

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Yes and no.
Yes if you are close up to the diamond.
No if you are a long way away as the intensity of the flash will be too dim to notice.
I suppose this would depend on two important factors..., the faceting style (e.g. large vs. small facet surfaces) and the light environment of the moment.

I have seen some antique diamonds throw noticeable flashes a mile away..., (not really but from extreme distances within the lighting environmental space).

BTW..., great explanation John
 

Paul-A

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Hello John,

Kudos to you for trying to clarify something as difficult as the difference between Dispersion and Fire. Indeed, both are often mixed up, leading to simplified and often wrong conclusions. Congrats to you for trying to untangle this.

Do forgive me however if I suggest some tweaking to your article, in order to reduce potential confusions.

“When they talk about dispersion they’re referring to a scientifically repeatable phenomenon. Diamond, as a material, reliably disperses light the same way, diamond after diamond after diamond. Every diamond on the planet has the same refractive index (it’s 2.4175, by the way #nerdstuff).”

Actually, refraction is the result of different colors (different wavelengths) having different refractive indexes, around the average refractive index of diamond (which also might deviate a little). Refraction thus is a fairly constant phenomenon, while dispersion is a function of the incident angle. For instance, with an incident angle of 90°, refraction leads to zero dispersion.

What is most important is that Dispersion is thus diamond-specific, while still not being the same as Fire. Like you state later in the article, all other measures equal, a higher and somewhat steeper crown on average leads to a higher potential Dispersion, because higher incident angles upon exiting the diamond are created.

“Diamond experts have known for a long time that high crowns and small tables (like antique diamonds) promote more visible fire because rays of light travel through more diamond material and disperse more. But this combination also produces less light return, therefore less brightness.”

I am confused here by the usage of ‘light return’, ‘brightness’ and ‘fire’. Total light return is the sum of brightness and fire. Like you very clearly explained, a dispersive fan exiting a diamond may be observed as Fire or as Brightness, depending amongst other things on the light source and the pupil and position of the observer. The fan may thus be observed as either Fire or Brightness, but it is definitely Light Return.

These antique diamonds generally produce less light return indeed, but their design promotes bigger dispersive fans, thus a higher probability of observing Fire, which as a result is not observed as Brightness.

What is most important is that more Light Return does not mean less Fire. If a dispersive fan is not observed as Fire, it is observed as Brightness. If in comparison, there is no dispersive fan, because of no light return, there is neither Fire nor Brightness.

I am already looking forward to your article on Scintillation. Contrast in movement is also an important driver in Dispersion and the observation of Fire. Especially the intensity in the change between dark and light returned is an important factor in the observation of Fire and Brightness. While you already did a great job at making a distinction between Dispersion and Fire, I wonder how you will approach Scintillation. Wishing you luck.

Live long,
 

Garry H (Cut Nut)

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I suppose this would depend on two important factors..., the faceting style (e.g. large vs. small facet surfaces) and the light environment of the moment.

I have seen some antique diamonds throw noticeable flashes a mile away..., (not really but from extreme distances within the lighting environmental space).

BTW..., great explanation John

I believe it is the Orlov or Orloff in the vault in Moscow - Sergey noted that you could walk slowly away from a flash from a huge facet and still follow the dispersion for as far away as you could get. Maybe 20 metres. But it is a huge diamond.
 

diagem

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I believe it is the Orlov or Orloff in the vault in Moscow - Sergey noted that you could walk slowly away from a flash from a huge facet and still follow the dispersion for as far away as you could get. Maybe 20 metres. But it is a huge diamond.
Exactly..., and this from a Mughal style (Orlov) diamond with "no" pavilion facet section at all!!

Not as large as the Orlov (only 5 ct vs. 200 ct +/-) but to what distance do you think such a flash is visible (taking in account a considered and enclosed space)?


Mughalflash1.jpg
 

Garry H (Cut Nut)

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Exactly..., and this from a Mughal style (Orlov) diamond with "no" pavilion facet section at all!!

Not as large as the Orlov (only 5 ct vs. 200 ct +/-) but to what distance do you think such a flash is visible (taking in account a considered and enclosed space)?


Mughalflash1.jpg

On behalf of Karl - what is the light source?
 

Garry H (Cut Nut)

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Not a normal viewing situation, so fail Yoram ;-)
You must have seen me write "never ever look at diamonds in direct sunlight"
In this case you are looking via a large enough window - mirror - window to do damage to your eyes. Eyes that are your livelyhood.
And stop with the next example too - the laser pointer :cool2:
 

Karl_K

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Even a relatively small diamond can send fire blasts a long distance when hit by a spotlight in an otherwise dim to dark room.
The relationship of the viewer, diamond and light angle and location has to be just so to see it directly.
Seeing the light on a wall or ceiling is more likely.
 

Cerulean

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Fascinating blog. I am not one of the more well-versed #cutnerds on PS, but I am currently studying visual perception (including anatomy and human visual experience) as it relates to graphical interfaces, and this is interestingly relevant.

It would follow that our perception and its limitations would have serious implications on cutting design, not unlike other designed products. This implies that designs that favor an optimal viewing experience in as many scenarios as possible will be favored by consumers. They may never think about why, but consumers on PS regularly cite that they "select stones with their eyes" - especially old cuts.

If I draw an analogy, a person perceiving darkness in their well-cut diamond (let's say, in bright, direct sunlight) experience it as an error, right? I.e. they might decide then that it's a bad product, or seek reassurance that something isn't wrong with their diamond.

Preventing as much error as possible is crucial in human-computer interaction - was curious if that logic carried through in the diamond industry.
 

diagem

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Not a normal viewing situation, so fail Yoram ;-)
You must have seen me write "never ever look at diamonds in direct sunlight"
In this case you are looking via a large enough window - mirror - window to do damage to your eyes. Eyes that are your livelyhood.
And stop with the next example too - the laser pointer :cool2:

Its definitely a normal viewing situation in my part of the world.., at least 9 months out of the year. Now for real.., I believe gems & diamonds should be shown in various real life lighting environments, sunlight being one important one.

Besides..., I love the way my diamonds play the lights in total sunlight..., they like it and they handle themselves great in such scenarios...

Light box photography is a total stage performance.
 

Garry H (Cut Nut)

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Fascinating blog. I am not one of the more well-versed #cutnerds on PS, but I am currently studying visual perception (including anatomy and human visual experience) as it relates to graphical interfaces, and this is interestingly relevant.

It would follow that our perception and its limitations would have serious implications on cutting design, not unlike other designed products. This implies that designs that favor an optimal viewing experience in as many scenarios as possible will be favored by consumers. They may never think about why, but consumers on PS regularly cite that they "select stones with their eyes" - especially old cuts.

If I draw an analogy, a person perceiving darkness in their well-cut diamond (let's say, in bright, direct sunlight) experience it as an error, right? I.e. they might decide then that it's a bad product, or seek reassurance that something isn't wrong with their diamond.

Preventing as much error as possible is crucial in human-computer interaction - was curious if that logic carried through in the diamond industry.

In this article we discuss at great length matters of human perception including the biology and mechanisms as they pertain to diamonds. Especially the fact that we view diamonds with two eyes.


"This study describes how visual properties determine the perception of a diamond's appearance and its performance attributes of brilliance, scintillation and fire, and how these influence beauty. Further articles will describe other parts of our cut study project. This research enables the development of methods and instruments for diamond performance analyses, shifting from diamond cut rejection tools, to diamond performance scoring systems, and the introduction of a new consumer language for communication between buyers and sellers. The proposed Performance Scoring System is consumer friendly and can be used to design and manufacture new diamond cuts with improved optical appearance."
 

Garry H (Cut Nut)

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Its definitely a normal viewing situation in my part of the world.., at least 9 months out of the year. Now for real.., I believe gems & diamonds should be shown in various real life lighting environments, sunlight being one important one.

Besides..., I love the way my diamonds play the lights in total sunlight..., they like it and they handle themselves great in such scenarios...

Light box photography is a total stage performance.

As Cerulean mentioned 2 posts above Yoram, can't tell you how many times in 21 years on this forum I have had to calm people down who are panicking because their diamond looks bad in sunlight.
I do know about sunlight too, as you know I live in an under-polluted paradise.
 

Diamond Girl 21

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In this article we discuss at great length matters of human perception including the biology and mechanisms as they pertain to diamonds. Especially the fact that we view diamonds with two eyes.


"This study describes how visual properties determine the perception of a diamond's appearance and its performance attributes of brilliance, scintillation and fire, and how these influence beauty. Further articles will describe other parts of our cut study project. This research enables the development of methods and instruments for diamond performance analyses, shifting from diamond cut rejection tools, to diamond performance scoring systems, and the introduction of a new consumer language for communication between buyers and sellers. The proposed Performance Scoring System is consumer friendly and can be used to design and manufacture new diamond cuts with improved optical appearance."

Wow! Very exciting!
 

Cerulean

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In this article we discuss at great length matters of human perception including the biology and mechanisms as they pertain to diamonds. Especially the fact that we view diamonds with two eyes.


"This study describes how visual properties determine the perception of a diamond's appearance and its performance attributes of brilliance, scintillation and fire, and how these influence beauty. Further articles will describe other parts of our cut study project. This research enables the development of methods and instruments for diamond performance analyses, shifting from diamond cut rejection tools, to diamond performance scoring systems, and the introduction of a new consumer language for communication between buyers and sellers. The proposed Performance Scoring System is consumer friendly and can be used to design and manufacture new diamond cuts with improved optical appearance."

This is so cool - thanks for sharing!
 

Starstruck8

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In this article we discuss at great length matters of human perception including the biology and mechanisms as they pertain to diamonds. Especially the fact that we view diamonds with two eyes.


"This study describes how visual properties determine the perception of a diamond's appearance and its performance attributes of brilliance, scintillation and fire, and how these influence beauty. Further articles will describe other parts of our cut study project. This research enables the development of methods and instruments for diamond performance analyses, shifting from diamond cut rejection tools, to diamond performance scoring systems, and the introduction of a new consumer language for communication between buyers and sellers. The proposed Performance Scoring System is consumer friendly and can be used to design and manufacture new diamond cuts with improved optical appearance."

Great article! Folks, you just have to check out the stereo pairs. The individual images look flat. Stereo fused, they positively shimmer, almost like the real thing.
 

diagem

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Fascinating blog. I am not one of the more well-versed #cutnerds on PS, but I am currently studying visual perception (including anatomy and human visual experience) as it relates to graphical interfaces, and this is interestingly relevant.

It would follow that our perception and its limitations would have serious implications on cutting design, not unlike other designed products. This implies that designs that favor an optimal viewing experience in as many scenarios as possible will be favored by consumers. They may never think about why, but consumers on PS regularly cite that they "select stones with their eyes" - especially old cuts.

If I draw an analogy, a person perceiving darkness in their well-cut diamond (let's say, in bright, direct sunlight) experience it as an error, right? I.e. they might decide then that it's a bad product, or seek reassurance that something isn't wrong with their diamond.

Preventing as much error as possible is crucial in human-computer interaction - was curious if that logic carried through in the diamond industry.
Fascinating point of view...

I'll start with the end.., The only (well mostly) logic marketing in the diamond industry is still based on historical methodic..., sell by weight and a lot. There are several cut options to choose from and good luck. That's the current norm!

In recent years some more specialized niches were born offering different or more value elements but mostly still catering to the usual normal mentioned above.

The industry at large is still busy pushing supply than listening to consumers for what they really want..., the genuine demand side.

Just like people understand the logic behind darkness in diamonds in a dark, unlit environments they should know that any overwhelming (of practically anything) disrupts the reality of things so does bright direct sunlight on most normal diamonds.

The beauty of diamonds is not just light performance based.., IMO, diamond material and proportional three dimensionality can offer great visuals even in the strongest sunlight. But if we are referring to 90%+ of diamonds cut in the last century, three dimensionality was not a strong point.
 
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