Language to describe fancy cuts with High Brilliancy, Fire , Scintillation

[mrs-b]

To sell a product you need demand. It can either generate naturally, or you can try to create demand. But to create demand you need to reach out directly to your market.

So here's a microcosm of industry and market interaction - right here in this thread. PS is a consumer forum. A number of consumers are responding to your comments and contributing to the conversation. Their comments are being entirely ignored. If you just want to chat to each other - no problem! Start a group email. But if you want to contribute to a consumer forum, and ask our opinion, respond to what we say. Until industry stops treating the consumer as tho they are either just a wallet, or alternately, ignorant, connection between the two will never happen. Does the industry indeed have something to offer me as the consumer? I don't know. Convince me.

And enough with the abbreviations and jargon pls. I'm here to learn. Jargon teaches nothing.

 

[Rockdiamond]

Hi David, thanks for your comment. If I understand right, the green in the ASET chart is a light coming from a rather small angle of incidence (measured from the girdle plane) and it is definitely not a leakage. In the various scope charts the leakage appears either as dark or white spots (depending on the scope and the light direction).
I use the term "leakage" in the same sense Tolkowsky uses it in his book and there it is necessarily a lost light and a bad thing... So I am confused now as to how do you interpret this term. And to get rid of my misconceptions I would love to see a diamond of any shape using leakage as a part of amazing light performance. If possible together with a similar stone without a leakage and worse light performance...

Vinnie- you're welcome- and thank you for the nice conversation!

Pretty much any well cut Fancy Colored Cushion/Radiant uses leakage.
Many older colorless stones do as well.
Plus there are "spready" stones. These are diamonds that are far shallower than average- easily dismissed by folks using numbers to eliminate stones.
Some shallow stones do suffer due to to the depth- but it's by no means guaranteed.
I do have a stone here - a fancy color stone- which is too shallow, in a negative manner.
I may try to get pics of what bothers me about the Light Performance.

And the thing about green......if you want your diamond to behave the way it does in an ASET, you'll need to make sure the table is perpendicular to your pupil. What's the likelihood of that? At almost any angle, green in the aset can be a bright area in the diamond.

 

[VinniePooh]

Pretty much any well cut Fancy Colored Cushion/Radiant uses leakage.

Well the thing about colored stones - they act as a band-pass filter - only their own color goes through/back. Everything else is to great extent filtered out (especially in intense/vivid). So one necessarily loses refraction - 'fire'. What is left is just reflection - for both brilliance and scintillation. However since only one color gets reflected - the total intensity and thus total brilliance is reduced. I guess that the darker the color of the stone - the less internal reflections and the more first surface reflections one gets. In this case some carefully introduced leakage may indeed be advantageous as it may provide optical 'depth' to the stone.

The leakage in the stone shown here (thanks, @OoohShiny ):

Do check out @diagem's ASET images of the 'vintage-y asscher' that @Jimmianne purchased from him:
https://www.pricescope.com/communit...-code-name-mildred.236249/page-6#post-4337522
and also his explanation in the linked thread.

is not intended. I believe it neither helps, nor distracts, since the total area of leakage (white spots) is pretty small compared to the total face area. Even when tilted. It also shows that one does not need to "to make sure the table is perpendicular to your pupil".

PS
It's a deep night here in Europe, so I'll take a break and continue tomorrow. Thanks to everyone!

 

[Serg]

Given the fact that a diamond is just a piece of stone, the desire to possess it stems from a combination of two factors - its 'life' (brilliance + fire + scintillation) and its rarity
...

Now I do understand that there is a difference between the brilliance / fire / scintillation and different cuts can optimize for more of the brilliance or more fire or more scintillation.

..

Anyway, after reading Tolkowsky's book, I think the main problem of the fancies is not the lack of language, but Tolkowsky himself:
His postulate that "The design of a diamond or of any gem-stone must be symmetrical about an axis, for symmetry and regularity in the disposition of the facets are essential for a pleasing result".
And his closing sentence: "That some new shape will be evolved which will cause even greater fire and life than the brilliant is, of course, always possible, but it appears very doubtful, and it seems that the brilliant will be supreme for, at any rate, a long time yet."
So until someone can (mathematically) prove that any shape other than round can be as live as a round one - fancies imho will never enjoy the same popularity.

What is mathematical prove in such case( for diamond "Life")? why does it best "prove" for diamonds?
Suppose I have a fancy cut that has similar or better "Life" them AGS0 H&A with same visual size.
Will you reject direct comparison until somebody publish 'Mathematical prove'?

Does mathematical prove for "Life" possible without mathematical description of "Life"?

 

[Serg]

So until someone can (mathematically) prove that any shape other than round can be as live as a round one - fancies imho will never enjoy the same popularity.

I doubt in strong correlation between mathematical prove and fancy cut popularity.
Few consumer will read and understand mathematical article about diamond "life".

 

[Serg]

Consumers' scores work reliably only with mass products. One needs a big number of reviews to get a statistically valid result. That could happen with synthetic diamonds/gems if they will be cheap and popular enough to make big sales.
..

it has been done for Modern Tolkowsky cut and it is possible to do same for many fancy cuts.

I believe the most* consumers are not happy with small variations in cuts . They prefer same as best reference sample.

They reject small deviation from "Ideal reference" and in same time they need big diversity in Designs, Shapes.

So if we have 100-1000 difference Designs( several Pattern facet designs for each cut type as:Emerald, Princess, Oval, Cushion, Heart, etc) and could repeat design with very high accuracy( 0.1 degree or better) then consumers review will start work.

We need try to use in diamond industry the business model: Production On demand , based on consumers reviews, consumers scores.
It could solve a lot of problem in diamond industry .

* Some consumers prefer wabi-subi style even in diamonds.

 

[VinniePooh]

Hi Serg,

thank you for your reply.

What is mathematical prove in such case( for diamond "Life")? why does it best "prove" for diamonds?

Mathematical proof is an analysis that will derive the optimal design for total reflection + maximized refraction, similar to what Tolkowsky did. I believe, such analysis is possible for every imaginable shape and am surprised that in the 100 years nobody undertook such analysis. It's not a rocket science there.

Suppose I have a fancy cut that has similar or better "Life" them AGS0 H&A with same visual size.

According to Tolkowsky a fancy cut can never by better than a round one (btw. I strongly disagree).

Will you reject direct comparison until somebody publish 'Mathematical prove'?
Does mathematical prove for "Life" possible without mathematical description of "Life"?

Without mathematical proof there is no objective optimal reference. Anything else is highly subjective. Moreover, human vision is not perfect and prone to manipulations (by clever shop lighting for example). So no, without proven optimum I won't trust my own eyes, not speaking of somebody else's verbal descriptions.

I doubt in strong correlation between mathematical prove and fancy cut popularity.
Few consumer will read and understand mathematical article about diamond "life".

Tolkowsky book was not intended for consumers, it was intended for those in trade: "This book is written principally for students of precious stones and jewellers, and more particularly for diamond manufacturers and diamond cutters and polishers."
However it outlined a common standard against which everyone can judge and from which consumers have ultimately profited. Moreover since many online sellers do use this standard as a marketing tool, I see a direct correlation between the Tolkowsky proof and the popularity of the round brilliant cut. And lack thereof of the fancies.

They reject small deviation from "Ideal reference" and in same time they need big diversity in Designs, Shapes.

I see no contradiction here. Every single shape, however unique it may be, has its own optimal cut. So there is an optimal heart brilliant cut, there is an optimal asher, oval, princess and so on. Even optimal 'map-of-your-country' brilliant cut. Actually such a proof will both unlock the creativity of the cutters/designers and will allow the labs to certify individual items.

 

[Serg]

Hi Serg,

thank you for your reply.


Mathematical proof is an analysis that will derive the optimal design for total reflection + maximized refraction, similar to what Tolkowsky did. I believe, such analysis is possible for every imaginable shape and am surprised that in the 100 years nobody undertook such analysis. It's not a rocket science there.

Yes, it is very easy to calculate total reflection+refraction but it has not correlation with "Life", Brilliancy, Fire.
Mirror has almost 100% Light Return and Zero Life, Brilliancy, Fire.
Mirrored disko ball create good Scintillation

Moreover since many online sellers do use this standard as a marketing tool, I see a direct correlation between the Tolkowsky proof and the popularity of the round brilliant cut. And lack thereof of the fancies.

Tolkowsky work has several mathematical , logical mistakes and unproved statements.
see for example

http://www.gemology.ru/cut/english/tolkow/tolk2.htm

"Now we know that the angle of dispersion is proportional to the sine of the angle of refraction. It is, moreover, proved in optics that the amount of light passing through a surface as at AB is proportional to the cosine of the angle of refraction. The brilliancy produced is proportional both to the amount of light and to the angle of dispersion"



Tolkowsky did not optimize Round brilliant cut.

Round cut had very good "Life" before his calculations. As I understood from his work, He firstly selected best round diamonds samples, measure angles then did his student work.
it was good attempt for his time.


round cut is popular for other reasons:
1) It had been very well optimised by whole diamond industry in several centuries by trial and error method.
2) it is much more simple for cutting in compare with most fancy cuts. cutters could reproduce it with much higher accuracy then fancy cuts
3) Good combination of yield and "Life" for big range of rough
4) Very good table/pavilion color ratio for colorless rough( Short raytracing from crown direction. )
5) Strong support from GIA cut grading. BTW Tolkowsky work is known now mainly due promotion from GIA.
6) One cut business model is more convenient profitable for current retail system

 

[OoohShiny]

I see no contradiction here. Every single shape, however unique it may be, has its own optimal cut. So there is an optimal heart brilliant cut, there is an optimal asher, oval, princess and so on. Even optimal 'map-of-your-country' brilliant cut. Actually such a proof will both unlock the creativity of the cutters/designers and will allow the labs to certify individual items.

If I am reading things correctly, I think the argument is that 'optimal' does not always equal 'beauty', and that identifying one single 'best' cut for any given shape risks standardisation and a reduction in variety/creativity (identified as an issue in MRBs), whereas we need to identify a way to describe different cutting styles that doesn't infer there is one single 'best' option for each shape.

 

[OoohShiny]

The leakage in the stone shown here is not intended. I believe it neither helps, nor distracts, since the total area of leakage (white spots) is pretty small compared to the total face area. Even when tilted. It also shows that one does not need to "to make sure the table is perpendicular to your pupil".

I would have to let @diagem confirm if he deliberately cuts his vintage asschers to include leakage or not

He has stated that he cuts 'the old fashioned way', though, rather than relying entirely on light performance assessment tools, which I think shows the skill he has if he can produce that sort of quality by eye!

 

[VinniePooh]

Yes, it is very easy to calculate total reflection+refraction but it has not correlation with "Life", Brilliancy, Fire.
Mirror has almost 100% Light Return and Zero Life, Brilliancy, Fire.
Mirrored disko ball create good Scintillation

I agree that reflection and refraction alone are not sufficient conditions. But imho they are necessary conditions. Without reflection there can be neither brilliance nor scintillation and without refraction no fire.
I see it the following way:
Let's do some imaginary experiments.
1. Take a perfect sphere made of non-reflective material (either clear or opaque) - it has neither brilliancy, nor fire, nor scintillation.
2. Coat this sphere with reflective coating - we'll get a bright spot on it surface - a reflection from a light source and even in a diffuse light environment it will be a shiny object. So we get some brilliance, but no life yet.
3. Break the surface into facets (disko-ball) - suddenly, as you say, we have scintillation.
4. Let's take a cone made of clear refractive material, say diamond, and place it between the observer and a polychromatic light source - we'll get a constant rainbow, but no life yet.
5. Break the surface into facets - suddenly we get fire.
Conclusion 1: for brilliance one needs reflection.
Conclusion 2: for colors one needs refraction.
Conclusion 3: for fire and scintillation one needs faceting.
The last one gives 'life'. The first two depend only on the combination of proportions and angles and can be optimized for every shape. The last one is where the art comes into play - every faceting pattern will give different character and beauty to the stone.
I think that a stone, precisely cut to optimal proportions and angles (for a given shape) will exhibit life with many different faceting patterns. On the other hand, for a stone, cut way off the optimum to be alive, one needs a really skillful and creative cutter, and even then there is no garantee.
As an average consumer, I know that with an optimally cut stone I can't be wrong. Anything else is a matter of luck, decency of the salesmen and lighting conditions in the shop...

Tolkowsky work has several mathematical , logical mistakes and unproved statements.

True. Nevertheless, the idea of using a ray tracing analysis to optimize or prove performance is correct and can (and should) be applied to shapes other than round. Moreover, the industry had 100 years to find and correct the mistakes.

 

[Serg]

2. Coat this sphere with reflective coating - we'll get a bright spot on it surface - a reflection from a light source and even in a diffuse light environment it will be a shiny object. So we get some brilliance, but no life yet.

What is the Brilliancy for you? Do you see a Brilliancy in a mirror?
just any bright spot has not any Brilliancy for me.

 

[VinniePooh]

If I am reading things correctly, I think the argument is that 'optimal' does not always equal 'beauty', and that identifying one single 'best' cut for any given shape risks standardisation and a reduction in variety/creativity (identified as an issue in MRBs), whereas we need to identify a way to describe different cutting styles that doesn't infer there is one single 'best' option for each shape.

I don't say that optimal means beauty. I think optimal means a stone has more chances to be beautiful. Whereas cutting styles can reveal themselves in different faceting patterns. Not every round brilliant must be Hearts&Arrows. Though due to its round form the variability is indeed limited. But still there are attempts on faceting patterns:
http://www.shimansky.com/discover/diamond-shapes-and-cuts/all-shapes-and-cuts/brilliant-10
https://patents.google.com/patent/US3585764A/en
https://patents.google.com/patent/US5462474A/en
to cite a few.

Conversely, I don't think that changing proportions or angles way off the optimum will provide more, or different beauty. Shallow or deep cuts can perhaps better utilize the rough stone or make it appear bigger in a setting. But these are all advantages for the cutter/jeweler, not for the consumer. With one exclusion - black or dark colored diamonds that have no or little internal reflection, I would prefer a very shallow cut)))

 

[Serg]

Let's do some imaginary experiments.
1. Take a perfect sphere made of non-reflective material (either clear or opaque) - it has neither brilliancy, nor fire, nor scintillation.
2. Coat this sphere with reflective coating - we'll get a bright spot on it surface - a reflection from a light source and even in a diffuse light environment it will be a shiny object. So we get some brilliance, but no life yet.
3. Break the surface into facets (disko-ball) - suddenly, as you say, we have scintillation.
4. Let's take a cone made of clear refractive material, say diamond, and place it between the observer and a polychromatic light source - we'll get a constant rainbow, but no life yet.
5. Break the surface into facets - suddenly we get fire.
Conclusion 1: for brilliance one needs reflection.
Conclusion 2: for colors one needs refraction.
Conclusion 3: for fire and scintillation one needs faceting.
The last one gives 'life'. The first two depend only on the combination of proportions and angles and can be optimized for every shape. The last one is where the art comes into play - every faceting pattern will give different character and beauty to the stone.
.

What did we receive for mathematical prove of "life" for a fancy cut, from all these imaginary experiments?

Do you have any suggestion for "Life" metric that can be calculated and used as mathematical prove for a fancy cut ?

 

[VinniePooh]

What is the Brilliancy for you? Do you see a Brilliancy in a mirror?
just any bright spot has not any Brilliancy for me.

https://en.wiktionary.org/wiki/brilliance:

1. The quality of being exceptionally effulgent (giving off light).

https://en.wiktionary.org/wiki/effulgent:
Shining, resplendent, radiant.

Brilliance for me is the ability of an object to appear as if it were a light source. A mirror in general has no brilliancy. However, a mirror placed sufficiently far away (to reduce it to a small viewing angle, a spot), will appear brilliant when reflecting a light source. I bet no one can tell the difference between the white flash originating from a distant piece of a mirror and of white flash originating from a distant diamond of the same size.

 

[Serg]

https://en.wiktionary.org/wiki/brilliance:

1. The quality of being exceptionally effulgent (giving off light).

https://en.wiktionary.org/wiki/effulgent:
Shining, resplendent, radiant.

Brilliance for me is the ability of an object to appear as if it were a light source. A mirror in general has no brilliancy. However, a mirror placed sufficiently far away (to reduce it to a small viewing angle, a spot), will appear brilliant when reflecting a light source. I bet no one can tell the difference between the white flash originating from a distant piece of a mirror and of white flash originating from a distant diamond of the same size.

It is more similar to Scintillation than to Brilliancy .
For me any single light spot has not both of them: Brilliancy and Scintillation .

 

[VinniePooh]

What did we receive for mathematical prove of "life" for a fancy cut, from all these imaginary experiments?

These experiments do not prove 'life' for a fancy cut. They show the necessary conditions for 'life' in any cut.

Do you have any suggestion for "Life" metric that can be calculated and used as mathematical prove for a fancy cut ?

How about
1. The average amount of rotation needed to see the next flash/fire from any given orientation in any rotation plane.
2. Partition of the viewing hemisphere into regions where white flashes/fire possible/visible and where not.
3. Average intensity of the flashes/fire for a given light source and distance.
4. Minimum distance from which the different colors of the fire can be distinguished.

 

[VinniePooh]

It is more similar to Scintillation than to Brilliancy .
For me any single light spot has not both of them: Brilliancy and Scintillation .

So what are the industry-standard definitions of
Brilliancy
Scintillation
Fire

Above terms must be crystal-clear for both the industry and the consumers long before we start speaking about abstract things like a life of a stone. I thought I do understand those terms, but this can be yet another misconception on my part...

 

[Rockdiamond]

Shallow or deep cuts can perhaps better utilize the rough stone or make it appear bigger in a setting. But these are all advantages for the cutter/jeweler, not for the consumer.

I’m the case of a well cut, yet shallow fancy shaped diamond the consumer gets a stone that looks larger or costs less than another stone of a similar price. Which is a win for a large percentage of folks looking to buy a diamond.
This is one of many assumptions that just don’t meet reality

 

[Serg]

These experiments do not prove 'life' for a fancy cut. They show the necessary conditions for 'life' in any cut.



How about
1. The average amount of rotation needed to see the next flash/fire from any given orientation in any rotation plane.
2. Partition of the viewing hemisphere into regions where white flashes/fire possible/visible and where not.
3. Average intensity of the flashes/fire for a given light source and distance.
4. Minimum distance from which the different colors of the fire can be distinguished.

So you suggest Averaging approach to calculate Fire.
In such case Diamond with 2 small Color flashes and diamond with 1 big Color flash (with same total area = sum of small flashes areas )will give same Fire for you. Right?
And 1 bright color flash gives same fire as 2 flashes with same area but half intensity. Right?

 

[Serg]

So what are the industry-standard definitions of
Brilliancy
Scintillation
Fire

Above terms must be crystal-clear for both the industry and the consumers long before we start speaking about abstract things like a life of a stone. I thought I do understand those terms, but this can be yet another misconception on my part...

Congratulation with the Question!
The Industry has NOT standard definition of Brilliancy, Scintillation, Fire!

You could find more about different definitions from diamond industry here:
http://www.gem.org.au/ckfinder/userfiles/files/GAA_Journal_V25_No3_web2(1).pdf

see pages 85-85.

"Cut group" definitions you could find few pages later

 

[VinniePooh]

So you suggest Averaging approach to calculate Fire.
In such case Diamond with 2 small Color flashes and diamond with 1 big Color flash (with same total area = sum of small flashes areas )will give same Fire for you. Right?
And 1 bright color flash gives same fire as 2 flashes with same area but half intensity. Right?

Serg, these are suggestions, as you pointed out. You don't have to accept them. These can be rejected, supplemented, replaced with other. I think these four are a good combination of metrics to start of. Neither of these is sufficient as a single metric.

 

[Serg]

Serg, these are suggestions, as you pointed out. You don't have to accept them. These can be rejected, supplemented, replaced with other. I think these four are a good combination of metrics to start of. Neither of these is sufficient as a single metric.

I would like to show You that Easy Mathematical prove is not possible at all. It is rocket science.
If we use Complex mathematical Prove then few consumers in world will understand it.
So Mathematical prove is wrong way for fancy cuts promotion. it will not work at all.

and in any case we have to create the language .

 

[Rockdiamond]

VinniePooh

Are you posting as a trade member or a consumer?

 

[blueMA]

True. Nevertheless, the idea of using a ray tracing analysis to optimize or prove performance is correct and can (and should) be applied to shapes other than round. Moreover, the industry had 100 years to find and correct the mistakes.

VinniePooh - you certainly don't seem like an average consumer and you've done more than adequate research to wade through the diamond industry conundrum - I completely understand where you're coming from.

While we're currently able to somewhat quantify light performance of stones to help reject potential poor performers these days, we may soon realize some years from now that the current reflector based systems based on assumptions are also quite limited for determining the actual overall beauty of diamonds for real world application. I'm not sure if we necessarily had it so wrong back 100 years ago, because some older cuts such as OEC, OMC, small SC are making a comeback.

Diamond is also a luxury commodity - people are not only drawn to the light performance of the rounds, but also know that rounds tend to be more costly than fancy cuts despite being easier cut, which tends to increase the demand for certain population.

You may want to visit this fascinating thread where @Miki Moto prefers her not-so-perfect stone compared to her two HOF super-ideal cut stones. People react very subjectively to brilliance/fire/scintillation, and their general exposures to the available lighting.

https://www.pricescope.com/communit...a-signature-super-ideal-diamond.174235/page-4

 

[VinniePooh]

Are you posting as a trade member or a consumer?

First time consumer. It just so happened that my fiancee does know a thing or two about diamonds and I had no choice but to dive head on into the subject...
I am an engineer (mechanical/aerospace)

 

[Rockdiamond]

Welcome, Vinnie.
You're making a lot of definitive ( and inaccurate) statments....if that matters to you.
Diamonds are NOT rocket science. ( not to contradict Sergie- it seems that from his perspective, measuring aspects of them are)
They're also not mechanical.

 

[VinniePooh]

You're making a lot of definitive ( and inaccurate) statments....if that matters to you.

It does. Being corrected is part of every education...

 

[Rockdiamond]

Being corrected is part of every education...

Exactly!!

To better inform you why I take my position: my training- which was completely hands on. The only tools were loupe and tweezer- and of course, eyes. So I have been on one side of this discussion for many years- but like you, I also have learned a lot.

 

[blueMA]

First time consumer. It just so happened that my fiancee does know a thing or two about diamonds and I had no choice but to dive head on into the subject...
I am an engineer (mechanical/aerospace)

I wonder if you're my nephew who works at NASA propulsion?