Brilliance, Fire, Scintillation, what are correct definitions?

[Serg]

Date: 5/4/2010 8:35:02 AM
Author: Paul-Antwerp

Date: 5/3/2010 1:08:30 PM

Author: ChunkyCushionLover


I hope this suggestion does not offend anyone, but the easiest way to break new ground is to build on top of currently published literature. One of my favourite works relevant to this discussion would be this article http://www.agslab.com/spie/spie_lo_res.pdf and its definitions and explanation therein.


I think it would be significantly easier to add, clarify, or modify the peer reviewed definitions found in this article than try to reinvent the wheel.


Gem Brilliance - Gemstone brilliance refers to the ability of a stone to appear illuminated to an observer. For this to occur light must be

directed from the virtual facets to the observer’s eyes. .... For understanding the illumination appearance of a gem it is useful to think of a gem’s facets and their optical projections,

the virtual facets, as a collection of tiny prisms that direct light to an observer’s eyes. Brilliance [can be defined] as the percentage by area of such tiny

prisms that can direct light to the observer’s eyes. This definition is simple and does not intend to account for obliquity factors that could be included to account for differences

in the relative position of facets or illumination conditions.


Gem Contrast - The high angular range ... indicates the zones in a stone crown that are not

illuminated due to the obscuration of the observer’s head. This obscuration produces what is known in the trade as

gem contrast. In proper amount and distribution, contrast creates structured lighting that enhances brilliance,

fire, and scintillation. Contrast can be a detrimental effect if t is significantly localized. Too little contrast results in a

stone appearance lacking variety under broad diffused illumination. Too much contrast results in a stone that lacks

brilliance. The combination of positive contrast characteristics and brilliance properties in a gemstone is known as contrast brilliance.

When a gemstone is in movement the contrast pattern changes in form. This effect is called dynamic contrast and adds substantial appeal to the appearance of a stone.


Gem Fire - The phenomenon of fire is one of the most appealing effects in transparent gemstones. Under favorable conditions

fire makes individual facets appear fully colored with the rainbow hues. Fire inherently occurs due to the light dispersion upon refraction as light enters and exits a stone.

Three factors determine the amount of fire perceived from a facet, namely, the angular dispersion of light upon refraction from the gemstone, the angular subtend of the source,

and the angular subtend of the eye’s pupil in relation to the facet. To best observe fire it is required to have a localized source of light so that its angular subtend is much smaller

than the angular dispersion produced by the gem facet, essentially a point source. As different colored rays arrive to the eye from a facet, some of them enter the eye’s pupil and others are blocked producing a colored appearance of the facet In this process the boundary of the eye’s pupil plays a critical role in obstructing portions of the spectrum to achieve the colored facet appearance.


Gem Scintillation - In the presence of brilliance and fire the most appealing effect is gem scintillation. Thus there are two major scintillation effects, fire and flash scintillation. To observe them it is required that the stone, the observer, or the illumination conditions be in movement. Typically the observer tilts the stone back and forth to observe scintillation and naturally optimizes for the direction that maximizes scintillation. Without brilliance ... there cannot be fire since no light can be brought to the observer’s eyes. Without fire there cannot be fire scintillation as defined by the change of fire pattern. Flash scintillation can occur without fire scintillation and it is due to ight sources not small enough in angular subtend to produce fire, or to the inability of a stone to sufficiently disperse ight for a given position of the observer. White diffused illumination will wash out both scintillation effects. Sources that subtend a small angle will contribute more to produce a flash effect, the rapid turn on and off of the light

from a given facet, than sources that subtend larger angles. Thus fire scintillation is more vivid than flash scintillation. The amount of gem scintillation perceived is linked to the brilliance and fire of a stone. However, scintillation strongly depends on the change of illumination conditions. This change is primarily produced on purpose by the movement of the stone as it is admired.

Thank you for looking up these definitions, CCL.


Reading and re-reading them, I think that AGS did a fine job here. May I suggest that they replace the definitions currently used in the PS-tutorial?


Live long,

re: "Brilliance [can be defined] as the percentage by area of such tiny prisms that can direct light to the observer’s eyes. "

If this percentage depends from Light source positions, I do not see real difference between AGS and Imagem Brilliance definitions .
If this percentage does not depends from Light source positions, I do not know what AGS Brilliance is.

Imagem :"Brilliance: A measure of a stone''s overall strength of light return that represents its average light return in the face-up position. This measure is determined by computing the mean gray-scale value of all pixels within the face up view of a diamond. Brilliance is average light return."

 

[Paul-Antwerp]

The big difference is that Imagem tries to define it from the static face-up-position only.

In this definition however, one does not limit it to that static position, instead mentioning in a general way ''the ability to appear illuminated'', which seems in line with your goal to maximize a cut''s ability to redirect light from a random light-source to the observer''s eyes.

Live long,

 

[Serg]

Date: 5/4/2010 9:22:48 AM
Author: Paul-Antwerp
The big difference is that Imagem tries to define it from the static face-up-position only.


In this definition however, one does not limit it to that static position, instead mentioning in a general way ''the ability to appear illuminated'', which seems in line with your goal to maximize a cut''s ability to redirect light from a random light-source to the observer''s eyes.


Live long,

1)AGS Scintillation has direct link to the movement:

"To observe them it is required that the stone, the observer, or the illumination conditions be in movement. "

But AGS Brilliance has not any link to any movement.
2) there is huge difference between cut''s ability to redirect light from a random light-source to the observer''s eyes and LR( does not matter LR for face up position only or average LR for different diamond tilts)

 

[Paul-Antwerp]

Can you enlighten us?

 

[Serg]

Date: 5/4/2010 9:56:04 AM
Author: Paul-Antwerp
Can you enlighten us?

I am trying do it last 10 years at least.

Do you really want it?
If yes, please start from mirror examples in This 8 years old article:

http://www.gemology.ru/cut/english/grading1/index.htm

Garry and I recently published direct links to mirror examples. Did you check its?

 

[Serg]

There are two diamonds both of them are red in ASET/IS and have very high ( highest) Brilliance according ASG and Imagem definitions. But first shows a(random) single( but real) light source very often ( for example 1 time in average) and second shows the same single light source very rare( for example 0.2-0.5 in average)
do you know such diamonds? do you believe what such diamonds exist ?

First has high DETAS/ETAS, second Has low DETAS/ETAS.

 

[Paul-Antwerp]

Date: 5/4/2010 10:29:41 AM
Author: Serg

There are two diamonds both of them are red in ASET/IS and have very high ( highest) Brilliance according ASG and Imagem definitions. But first shows a(random) single( but real) light source very often ( for example 1 time in average) and second shows the same single light source very rare( for example 0.2-0.5 in average)
do you know such diamonds? do you believe what such diamonds exist ?

First has high DETAS/ETAS, second Has low DETAS/ETAS.

What you are saying, is:

Take diamond A, very red in face-up-ASET, but all the red is actually coming from only one light-source in the red area, it is a single light source shown very often.
Take diamond B, equally red in face-up-ASET, but the red is coming from multiple potential light-sources, a single light-source only lights up a small area of the red.

Is that correct?

If so, I definitely prefer theoretical diamond B far over diamond A.

As for definitions, according to Imagem, both would score the same.

In the AGS cut-grade, diamond A would not be bright at all in the tilted assessment, and I would think that it would get a very low cut-grade.

However, in the online-assessment of the stone, without an actual cut-grade and only a face-up static picture, diamond A would probably get a thumbs-up from most posters here.

All this of course under the premise that I understood you correctly.

Live long,

 

[Karl_K]

Date: 5/4/2010 10:29:41 AM
Author: Serg


There are two diamonds both of them are red in ASET/IS and have very high ( highest) Brilliance according ASG and Imagem definitions. But first shows a(random) single( but real) light source very often ( for example 1 time in average) and second shows the same single light source very rare( for example 0.2-0.5 in average)

do you know such diamonds? do you believe what such diamonds exist ?


First has high DETAS/ETAS, second Has low DETAS/ETAS.

yes I know such diamond designs and they exist.

Also important is that adjacent virtual facets while both showing red in ASET draw light from different areas of the red zone, they will give many intense flashes as the diamond is tilted if the virtual facets are not too large as one will provide contrast for the other in non-symmetrical lighting and movement while drawing light from the potentially brighter zone.

Also important is where is the VF drawing light from besides the red zone.
If it also draws light from the green zone it will flash more often.
Such a diamond with a lot of these will be described by its owner as a diamond that grabs light from anywhere and returns it to the viewer.
That is a good thing and something I take into consideration.

 

[Serg]

Date: 5/4/2010 10:47:41 AM
Author: Paul-Antwerp

Date: 5/4/2010 10:29:41 AM
Author: Serg

There are two diamonds both of them are red in ASET/IS and have very high ( highest) Brilliance according ASG and Imagem definitions. But first shows a(random) single( but real) light source very often ( for example 1 time in average) and second shows the same single light source very rare( for example 0.2-0.5 in average)
do you know such diamonds? do you believe what such diamonds exist ?

First has high DETAS/ETAS, second Has low DETAS/ETAS.

What you are saying, is:

Take diamond A, very red in face-up-ASET, but all the red is actually coming from only one light-source in the red area, it is a single light source shown very often.

No. I said nothing about only one light-source. Do you remember France Carre example from my and Yurii presetnation in IDCC1 2004?
this cut collect light mainly from two Directions ( ETAS is cross)

Take diamond B, equally red in face-up-ASET, but the red is coming from multiple potential light-sources, a single light-source only lights up a small area of the red.

Yes


Is that correct?

If so, I definitely prefer theoretical diamond B far over diamond A.

As for definitions, according to Imagem, both would score the same.

In the AGS cut-grade, diamond A would not be bright at all in the tilted assessment, and I would think that it would get a very low cut-grade.

1) I saw nothing about tilting in AGS Brilliance definition . but France Carre will collect light from similar directions during tilting, you need rotate thus cut in third axis to do diamond dark. Just tilting in two directions is not enough
2) I do not see any reasons for low cut-grade in AGS cut grading system( LR in ASET light is high even during tilting , angular dispersion( ASG FIRE) could be high too( it is possible to do), ASG Scintillation ( how often VF facets change color in ASET during tilting) could be high too). Am I wrong here?

However, in the online-assessment of the stone, without an actual cut-grade and only a face-up static picture, diamond A would probably get a thumbs-up from most posters here.

All this of course under the premise that I understood you correctly.

Live long,

 

[Karl_K]

Date: 5/4/2010 10:29:41 AM
Author: Serg


There are two diamonds both of them are red in ASET/IS and have very high ( highest) Brilliance according ASG and Imagem definitions. But first shows a(random) single( but real) light source very often ( for example 1 time in average) and second shows the same single light source very rare( for example 0.2-0.5 in average)

do you know such diamonds? do you believe what such diamonds exist ?


First has high DETAS/ETAS, second Has low DETAS/ETAS.

first: high crown asscher with small table
second: flat top asscher with a low crown and large table.

 

[Serg]

Date: 5/4/2010 11:49:57 AM
Author: Karl_K

Date: 5/4/2010 10:29:41 AM

Author: Serg



There are two diamonds both of them are red in ASET/IS and have very high ( highest) Brilliance according ASG and Imagem definitions. But first shows a(random) single( but real) light source very often ( for example 1 time in average) and second shows the same single light source very rare( for example 0.2-0.5 in average)


do you know such diamonds? do you believe what such diamonds exist ?



First has high DETAS/ETAS, second Has low DETAS/ETAS.

first: high crown asscher with small table

second: flat top asscher with a low crown and large table.

Karl, Could you publish ETAS images or dmc files?
My example was RBC( or Princess) and France Carre( or Baget)

 

[Karl_K]

Date: 5/4/2010 11:54:53 AM
Author: Serg

Karl, Could you publish ETAS images or dmc files?

My example was RBC( or Princess) and France Carre( or Baget)

Here is a (virtual)flat top that shows the issue.
very bright for an asscher, .90LR Stereo
It is even bright throughout a range of tilt.
looks pretty in static pictures in symmetrical lighting.
blah in the real world and when in motion, very little life.
The ETAS and DETAS show why.
I uploaded it as a gem file so everyone can play if they want.
Compare it in JS lighting to office lighting and you will see how off axis lighting kills this one.
This is not uncommon in real world asschers but they usually have less brightness than this one making them even worse.

 

[Rhino]

Greetings Paul. As a research gemologist who works with cutters I may be able to offer a unique perspective to your posting.

Date: 4/29/2010 10:16:34 AM
Author:Paul-Antwerp
The job of a cutter is different from that of a gemologist. Where a gemologist tries to describe certain appearances after the product is finished, a cutter has to basically foresee these appearances in design and in production.

True. What confuses things too are definitions that are assigned by labs to common optical terms that disagree too. One example coule be what GIA describes as patterned scintillation or what AGS defines as contrast. Both actually mean the same thing but each lab is actually looking at it differently.

GIA''s definition of patterened scintillation is simply the pattern of bright and dark reflections as it is observed in a diffused lighting environment and further broken down into "static patterned scintillation" or "dynamic patterned scintillation" (ie. still or moving). The patterning is either pleasing to the eyes or not. They''re not relying on any particular technology to determine this but relying on the human observation testing performed when determining their cut grading system. Some feel this system is too loose because it is not looking at features under any particular techology (for a more critical evaluation) but rather a fairly loose 5 grade system.

AGS on the other hand attempts to further define and grade this, instead calling it contrast and utilizing a technology in this attempt (blues in the ASET along with ray trace examination of the diamond and analysis of the distribution of blues/reds as the diamond is rocked and tilted to 45 degree angles). The problem here is blues, while very good indicators of contrast do not always accurate translate to head/body shadow. Hearts & Arrows is a perfect example because all 8 mains show up as blue in the ASET and rarely do you actually see all 8 mains go dark at the same time.

Between a cutter and a gemologist however, and more to your point ... I think it is important for both to be on the same page with regards to their definitions and that clear communication be established regarding whatever appearance they are talking about. Your vision for what the appearance is as a cutter may be different from the gemologist who is employing your services to cut.

Kind of like a salesman understanding the needs of his client. If we are helping a person with a setting and the client has an appearance in mind they are looking to accomplish it is the professional who must do his best to understand the needs of his client and carry out the execution to their liking. If the gemologist gives you specific instructions as to what he wants cut with regards to numbers just use the numbers he is giving you that will translate to the appearance he thinks it will accomplish. If you think those numbers will not translate to the appearance he is after communicate this and make your suggestion as to what you think are off in his numbers.

The advantage of being a cutter is that we can build upon experience, our own and that of predecessors, while the gemologist might still be struggling in ways to accurately describe. In that sense, we can produce diamonds, that gemologists have a hard time describing since they are still struggling with the definitions of certain descriptions.

I can understand if the gemologist does not know the numbers to produce the appearance he is after and is asking for your expertise in this matter. Then you must make suggestions as to what numbers will produce the desired optical effect. When we were working on the optical design of August Vintage cushions the cutter brought to the table what he knew from his years of cutting but was unfamiliar with cutting for specific type optics. When he carefully carried out my instructions he acheived precisely what I wanted. Veering from my specific instructions on facet angles in all directions misses the mark and the goal is not acheived. It all boils down to whose capital is at stake too. When you are cutting your own product you are cutting your interpreation of what you think it should look like and staking your investment on that. If a gemologist hires the employ of a cutting facility or decides to work with a particular cutter it is important they follow the gemologits'' instructions because he will be the one investing and marketing the final product and it is his capital at stake. At the same time I think it is wise for the gemologist to listen and hear whatever advice the cutter has but ultimately it is the one holding the bag at the end of they day who must be happy because it is his capital.

This introduction only served to explain that I am coming from a different background than most contributors here. However, I have tried to combine my hands-on-experience with an ever-growing knowledge of gemology. I see it as an advantage that I can consider certain basics of gemology and, as a relative newbie in this area, can pinpoint where a certain gemological definition or description is lacking in clarity.

Absolutely and why it is important for both cutter and gemologist to be on the same page. If certain angle combinations (in mains or minor facets) produce a certain appearance you think will improve a product you are cutting for someone and have evidence that it will do so I think the gemologist should be open to your suggestions.

Over the past years, I have concentrated on the gemological description of brilliance (contrast-brightness), fire and scintillation. Understanding these phenomena now a lot better, I am glad to see that the extra knowledge does not affect my designs or production. But I am shocked to see, on a gemological field, how these terms are often loosely and incorrectly used, hampering new developments in gemological knowledge.

Tell me about it. We hear all the time from suppliers/vendors/manufacturers how "bright" or how "brilliant" a diamond is and when it arrives is nothing like what we thought. It is rampant in the industry and even though GIA and AGS have gone through great strides to define these characteristics (and they are really not difficult to understand) we must also realize that when someone is describing a diamond as "brilliant" ... well ... the first question that goes through my mind is ... as compared to what?

An AGS light performance grade of 5-7 (GIA good) is "brilliant" and could be described as such but knowing what we know we immediately ask ... is it as brilliant as the H&A type goodies you and I are accustomed to? Not too long ago we published a video demonstrating optical differences between 2 round diamonds, both GIA Ex cut and both with HCA scores p]

Reading PS''s tutorial-page on the subject (link), I find it hard to understand, and in its attempt to be clear and short, often incorrect. Therefore, I would like to attempt to re-set these definitions. Here it goes:
''
Brilliance, fire and scintillation are traditionally mentioned as the three aspects of light, which jointly describe a beautiful diamond.

In order to better understand them, we need not only define them, but also pinpoint the difference between them. First, the definitions:

Brilliance, or contrast-brightness, is the white light returned and observed by an observer in relation to the contrast, caused by the observer obstructing the light and light-leakage.
Fire is the colored light returned and observed by an observer.
Scintillation is the combination of sparkles, white or colored, observed by an observer, when either the diamond, the light-source or the observer are moving.

Looking at scintillation specifically, there are two major differences with the other two. First, there is a need of movement, and second, scintillation comprises both white and colored light being observed. So, in a sense, brilliance and fire are subsets of scintillation.

Or it could be argued that scntillation is the subset of brilliance (what I commonly refer to as brightness) and fire. We do this in our tutorial''s on the subject.

What I think is important to understand about scintillation is that the type of scintilltion one will observe (patterned or sparkle) is entirely dependant upon the lighting they are observing the diamond under. Sparkle scintillation will be observed in spot lighting and patterned scintillation in diffuse.

On the date of today, it is safe to say that most gemological studies are still limited to studying ''potential brilliance''. As such, many gemological ''truths'' are still based upon a partial study of diamonds.
''
Looking forward to comments.

Agreed. I''ll read throuh the rest of this thread as time allows.

Regards,

 

[Garry H (Cut Nut)]

6am and off to gym

 

[Garry H (Cut Nut)]

.

 

[Paul-Antwerp]

Sergey,

I did not remember your ''French Carré''-example from IDCC, but Garry bringing up the slides from a later presentation (I think) shows the example.

As such, it clearly shows in an extreme example, the limitations of using the face-up ASET-pic as a definite instrument in grading potential brilliance. In the current atmosphere of PS, this is important information, and I have been beating that drum regularly.

For AGS, who have chosen to create a shape-dependent cut-grade in which the grade is dependent upon various tilted assessments, it does not seem to pose a problem, but it cannot be denied that also the AGS-cut-grade is merely a rejection-tool, and this because of various reasons.

Which brings us back to their definitions. You indicated that their definition of brilliance can be improved. I have the impression that you are hinting only at minor tweaking. What change would you suggest? And do you agree with the other definitions?

Live long,

 

[Serg]

Date: 5/5/2010 5:49:25 AM
Author: Paul-Antwerp
Sergey,


I did not remember your 'French Carré'-example from IDCC, but Garry bringing up the slides from a later presentation (I think) shows the example.


As such, it clearly shows in an extreme example, the limitations of using the face-up ASET-pic as a definite instrument in grading potential brilliance. In the current atmosphere of PS, this is important information, and I have been beating that drum regularly.


For AGS, who have chosen to create a shape-dependent cut-grade in which the grade is dependent upon various tilted assessments, it does not seem to pose a problem, but it cannot be denied that also the AGS-cut-grade is merely a rejection-tool, and this because of various reasons.


Which brings us back to their definitions. You indicated that their definition of brilliance can be improved. I have the impression that you are hinting only at minor tweaking. What change would you suggest? And do you agree with the other definitions?


Live long,

I am disagree with all 4 AGS definitions.
I gave my suggestions about Brilliance definition early. Before we agree in Brilliance I do not see reasons discuss others definitions.
My point what Brilliance can not be correctly defined as part of picture or even part of comics( set of static pictures), difference between comics and cartoon is critical for correct Brilliance definition.
Neither AGS definitions nor Imagem definition concern about this critical difference

BTW. French Carre type examples show more fundamental problems in ASG approach than just using Face up image in ASET( tilting does not fix its). AGS approach has huge problem with Scintillation also. I do not like discuss about Fire here( it is too complex issue)

 

[Serg]

"I can not give clear and full definition on English ( it is not easy task even for native speaking experts)

Try something as "The human brain sees Brilliance as united dynamical pattern of white( without flashes) , gray and black zones which is reflection secondary light sources during motion ( i.e. colored zones are eliminated). Scintillation is not united pattern, it is just dynamical set of flashes . very important part of Brilliancy is increased Brightness dynamical range due motion and contrast statical pattern.""

More technical definition ( just first attempt )

Brilliance is "low frequency" image changes ( due big angular size for secondary light sources), Scintillation is "high frequency'' image changes( due small angular size primary light sources)

for example Zero contrast will give zero frequency

Integral such functions could give metrics for Brilliance and Scintillation

 

[Garry H (Cut Nut)]

Date: 5/5/2010 6:28:50 AM
Author: Serg
''I can not give clear and full definition on English ( it is not easy task even for native speaking experts)

Try something as ''The human brain sees Brilliance as united dynamical pattern of white( without flashes) , gray and black zones which is reflection secondary light sources during motion ( i.e. colored zones are eliminated). Scintillation is not united pattern, it is just dynamical set of flashes . very important part of Brilliancy is increased Brightness dynamical range due motion and contrast statical pattern.''''

More technical definition ( just first attempt )

Brilliance is ''low frequency'' image changes ( due big angular size for secondary light sources), Scintillation is ''high frequency'' image changes( due small angular size primary light sources)

for example Zero contrast will give zero frequency

Integral such functions could give metrics for Brilliance and Scintillation

An attempt to help with the English on the first part. Is it correct Sergey?

Try something as "The human brain sees Brilliance as united dynamical pattern of white( without flashes) , gray and black zones which is reflection secondary light sources during motion ( i.e. colored zones are eliminated).

Scintillation is not united pattern, it is just dynamical set of flashes .

very important part of Brilliancy is increased Brightness dynamical range due motion and contrast statical pattern.""

"The human brain sees Brilliance as united (united could be ? cohesive ? ? integrated ?) dynamic patterns of white (without flashes), gray and black zones which are reflections of secondary light sources during motion (i.e. colored zones are eliminated).

Scintillation is not united or integrated patterns; it is only the dynamic set of flashes.

A very important part of Brilliancy is the increased Brightness because of the dynamic range due to motion and static contrast pattern."
Sergey – is it static or another word like these http://en.wikipedia.org/wiki/Visual_illusions

 

[Serg]

Date: 5/5/2010 7:47:23 AM
Author: Garry H (Cut Nut)

Date: 5/5/2010 6:28:50 AM

Author: Serg

'I can not give clear and full definition on English ( it is not easy task even for native speaking experts)


Try something as 'The human brain sees Brilliance as united dynamical pattern of white( without flashes) , gray and black zones which is reflection secondary light sources during motion ( i.e. colored zones are eliminated). Scintillation is not united pattern, it is just dynamical set of flashes . very important part of Brilliancy is increased Brightness dynamical range due motion and contrast statical pattern.''


More technical definition ( just first attempt )


Brilliance is 'low frequency' image changes ( due big angular size for secondary light sources), Scintillation is 'high frequency' image changes( due small angular size primary light sources)


for example Zero contrast will give zero frequency


Integral such functions could give metrics for Brilliance and Scintillation

An attempt to help with the English on the first part. Is it correct Sergey?


Try something as 'The human brain sees Brilliance as united dynamical pattern of white( without flashes) , gray and black zones which is reflection secondary light sources during motion ( i.e. colored zones are eliminated).


Scintillation is not united pattern, it is just dynamical set of flashes .


very important part of Brilliancy is increased Brightness dynamical range due motion and contrast statical pattern.''


'The human brain sees Brilliance as united (united could be ? cohesive ? ? integrated ?) dynamic patterns of white (without flashes), gray and black zones which are reflections of secondary light sources during motion (i.e. colored zones are eliminated).

Scintillation is not united or integrated patterns; it is only the dynamic set of flashes.

A very important part of Brilliancy is the increased Brightness because of the dynamic range due to motion and static contrast pattern.'

Sergey – is it static or another word like these http://en.wikipedia.org/wiki/Visual_illusions

Garry
, Thanks

re:. Brilliance as united (united could be ? cohesive ? ? integrated ?) dynamic patterns

could be cohesive pattern, but definitely can not be integrated pattern

it is as united front, united action,..

re:Scintillation is not united or integrated patterns; it is only the dynamic set of flashes.

Scintillation is not united or integrated patterns; it is only the dynamic set of random( or individual ) flashes. ( may be now difference is more clear . Random pattern is as opposite united pattern

 

[Paul-Antwerp]

Where I thought that I understood Sergey''s distinction between brilliance and scintillation two pages earlier, I now must say that I did not and do not.

Are you saying that in a light-environment with only secondary light sources, there is no scintillation?
Vice versa, in a light-environment without secondary light sources (If that exists), there is no brilliance?

Live long,

 

[Serg]

Date: 5/5/2010 8:48:00 AM
Author: Paul-Antwerp
Where I thought that I understood Sergey''s distinction between brilliance and scintillation two pages earlier, I now must say that I did not and do not.


Are you saying that in a light-environment with only secondary light sources, there is no scintillation?

Vice versa, in a light-environment without secondary light sources (If that exists), there is no brilliance?


Live long,

In Igloo you can not see Scintillation, under one spot light you can not see Brilliance, In ASET/IS you can not see Fire, Brilliance, Scintillation even if you are tilting diamond

a lot of primary light sources could be equally one secondary light. Light source angular size is important key for this approach
Both relation between angular dispersion and light source angle is critical for Fire and light angular size is important Brilliance. Small angular size is good for Fire and Scintillation but is bad for Brilliance

 

[Paul-Antwerp]

This is what I understand.

- In ASET/IS, you cannot see or judge Fire, nor Scintillation. I fully agree, and it is for me also one of the reasons why I describe them as rejection-tools.

- For Fire, both angular dispersion and the angular size of the light source and the relation between both are important. Absolutely, it makes the difference between observing a fiery colour or not.

Difficult to understand is:

- "In an igloo, you cannot see scintillation." Considering that an observer (not wearing white clothing) is present in the igloo, does that mean that the ''sparkle'' (on/off-effect) of some virtual facets as you move the stone is not scintillation in your definition?

- "Small angular size is good for Fire and for Scintillation". I understand your point for Fire, but can Fire not be observed in an igloo? Me not understanding your statement for Scintillation is actually connected to my question above.

Live long,

 

[Serg]

Date: 5/5/2010 10:43:17 AM
Author: Paul-Antwerp
This is what I understand.


- In ASET/IS, you cannot see or judge Fire, nor Scintillation. I fully agree, and it is for me also one of the reasons why I describe them as rejection-tools.


- For Fire, both angular dispersion and the angular size of the light source and the relation between both are important. Absolutely, it makes the difference between observing a fiery colour or not.


Difficult to understand is:


- 'In an igloo, you cannot see scintillation.' Considering that an observer (not wearing white clothing) is present in the igloo, does that mean that the 'sparkle' (on/off-effect) of some virtual facets as you move the stone is not scintillation in your definition?




- 'Small angular size is good for Fire and for Scintillation'. I understand your point for Fire, but can Fire not be observed in an igloo? Me not understanding your statement for Scintillation is actually connected to my question above.


Live long,

Just "On/off-effect " is not enough for "sparkles of light, flashes". For Flashes you need light source with brightness much more bigger than level of your eye brightness adaptation what is not possible for igloo even if you are using tuxedo .

 

[Karl_K]

Serg,;
I see what you mean, but that explanation is not going to work, head shadow will break up a single light source and produce scintillation at some point in some diamonds. An igloo can have many spotlights for lighting it is better to define the actual lighting.

The biggest thing that the current definitions of brilliance leaves out is contrast against the background.
Which of these diamonds is brighter?

 

[Karl_K]

Date: 5/5/2010 10:56:12 AM
Author: Serg



Just 'On/off-effect ' is not enough for 'sparkles of light, flashes'. For Flashes you need light source with brightness much more bigger than level of your eye brightness adaptation what is not possible for igloo even if you are using tuxedo .

I don't agree for a diamond someone is wearing, it just has to be brighter than the background if the background is significantly larger in all directions than the diamond which it will be unless the person is just holding up one finger.

 

[Serg]

Date: 5/5/2010 11:07:03 AM
Author: Karl_K
Serg,;

I see what you mean, but that explanation is not going to work, head shadow will break up a single light source and produce scintillation at some point in some diamonds. An igloo can have many spotlights for lighting it is better to define the actual lighting.


The biggest thing that the current definitions of brilliance leaves out is contrast against the background.

Which of these diamonds is brighter?

Karl, I do not see clear connection between my and your posts. Seems what you did not understand my statements .
I do not like argue with anybody here to proof my point of view about Brilliance, and other definitions . Sorry , I am not interesting argue with you too.

 

[Serg]

Date: 5/5/2010 11:14:29 AM
Author: Karl_K

Date: 5/5/2010 10:56:12 AM

Author: Serg




Just ''On/off-effect '' is not enough for ''sparkles of light, flashes''. For Flashes you need light source with brightness much more bigger than level of your eye brightness adaptation what is not possible for igloo even if you are using tuxedo .

I don''t agree for a diamond someone is wearing, it just has to be brighter than the background if the background is significantly larger in all directions than the diamond which it will be unless the person is just holding up one finger.

This statement shows what you are with me, but you just did not understand what you agree with me

I advice you to compare Floor, wall, ceiling brightness for example in office light conditions. it could be big surprise for you

 

[ChunkyCushionLover]

Date: 5/5/2010 6:05:18 AM
Author: Serg

Date: 5/5/2010 5:49:25 AM
Author: Paul-Antwerp
Sergey,


I did not remember your ''French Carré''-example from IDCC, but Garry bringing up the slides from a later presentation (I think) shows the example.


As such, it clearly shows in an extreme example, the limitations of using the face-up ASET-pic as a definite instrument in grading potential brilliance. In the current atmosphere of PS, this is important information, and I have been beating that drum regularly.


For AGS, who have chosen to create a shape-dependent cut-grade in which the grade is dependent upon various tilted assessments, it does not seem to pose a problem, but it cannot be denied that also the AGS-cut-grade is merely a rejection-tool, and this because of various reasons.


Which brings us back to their definitions. You indicated that their definition of brilliance can be improved. I have the impression that you are hinting only at minor tweaking. What change would you suggest? And do you agree with the other definitions?


Live long,

I am disagree with all 4 AGS definitions.
I gave my suggestions about Brilliance definition early. Before we agree in Brilliance I do not see reasons discuss others definitions.
My point what Brilliance can not be correctly defined as part of picture or even part of comics( set of static pictures), difference between comics and cartoon is critical for correct Brilliance definition.
Neither AGS definitions nor Imagem definition concern about this critical difference

BTW. French Carre type examples show more fundamental problems in ASG approach than just using Face up image in ASET( tilting does not fix its). AGS approach has huge problem with Scintillation also. I do not like discuss about Fire here( it is too complex issue)

I don''t understand what you disagree with in the AGS definition of Brilliance from Sassian et al.

[Their] definition is simple and does not intend to account for obliquity factors that could be included to account for differences
in the relative position of facets or illumination conditions.

For example, in typical illumination scenarios the relative intensity of light provided by light sources varies
significantly from place to place. This makes the inclusion of obliquity factors substantially irrelevant. In addition,
the definition is congruent with the intuitive idea that something brilliant is an object that can direct light to an
observer’s eye. Thus a gem is said to have the attribute of brilliance if it can direct light to the observer’s eyes. Effectively,
a brilliant gem can be equated with a structured light source.

If you disagree with that than please explain why as I still don''t get what the problem is.

 

[ChunkyCushionLover]

Date: 5/4/2010 3:44:05 PM
Author: Garry H (Cut Nut)
.

Re; ASET Carre Versus RB

Garry,

I feel we can easily put this recurring reminder to rest by saying that on PS ASETs should be compared within the same cut design and it is not always correct to use the same general rules to compare different facet designs.
AGS points out that each cut has its own set of performance standards and they are not held to the same standard as a round brilliant.

Further the Carre in AGS-PGS would surely have a penalty when tilting from -30 to +30 in 5 degree increments both in contrast and brightness. Even taking into account the most heavily weighted faceup image it would still receive substantial deductions. Similarly if one were to view the Carre diamond under ASET filters in 5 degree tilt incremements it would be readily noticeable how small the tilt range available really is where the Carre directs light most optimally back to the viewer.

I should also point out the most current model of AGS-ASET is a video feed with direct port to a computer and the intended functionality of offering ASET video, it is definitely their intention to provide this functionality. I feel retailors should provide video, especially in the cases of step cuts and other novel fancy shape designs.