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Bruce Harding on Fractioning of Color by a Gem

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pricescope

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Bruce Harding (aka Beryl) wrote an article Fractioning of Color by a Gem showing an effect of dispersion where color components are progressively diverted from the spectrum, as in 'fractional distillation' or 'fractional crystallization' of liquids.

Bruce demonstrates this effect on diamonds with multiple ray-tracing using DiamCalc software
 

belle

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thank you bruce, for taking the time to put this article together. it is always nice to see you here sharing your great knowledge.

love playing with that multiple ray trace option!
 

oldminer

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Looks pretty and shows the technical properties of DiamCalc. Would someone please explain what the demonstration shows in terms of diamond grading, valuation, gemology, etc? In other words, is there a real world use for such an understanding or is it for the sake of understanding alone? I'd like to appreciate it to the fullest extent and am not sure what the conclusions are.

THANK YOU.
 

beryl

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Dave:
It has no application value - certainly not for grading diamonds.
It illustrates and explains some things that are are of interest to those of us who want to know 'Why'.
Responses tell me that there are a few out there; that makes the effort worthwhile - like teaching..
I was delighted to see that DiamCalc was able to do this. Few folks use this feature, I am sure. For example, it is very interesting to see that yellow light is emitted when there is none in the source, and that it is only visible within a certain distance of the gem. This kind of knowledge could be useful in the design of display systems to show-off 'fire' in diamonds. It also shows why there is no green fire, even though there is green in the source of white light.

I wish that I could bottle the various colors as they are fractioned-off, as refineries do with petroleum distillates. The closest I know of this with light is the Japanese businessman who grew incredible tomatoes in his office, having directed sunlight from the roof of his building by some sort of conduit - apparently it selected favorable light and/or ignored unfavorable light. Imagine the financial implications of such a discovery! A good quest for some young person.
 

strmrdr

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kewl stuff thank you!
 

oldminer

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Thank you Beryl for the explanation. Maybe part of this has some effect on color grading of diamonds. I better understand what you were describing and that, to me, is important learning.
 

Garry H (Cut Nut)

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Nice explanations Bruce.

Very easy to follow – we have some Fire enthusiasts who love to take photo’s of their diamonds in sunlight etc and I hope they will read your article and get an understanding of what they see and why.

It has been interesting for me to learn about this field and Sergey has helped me understand a basic weakness in GIA’s Cut research – a recent communication from their study team indicates a continuing lack of understanding why we do not see green very often (GIA do not agree that “green flashes are rarely seen” as we wrote in the Australian Gemmologist April June 2006).


Finally Beryl, you are using a very old version of DiamCalc and you can upgrade to version 2.8 now. If there is a cost I will bear it as a Christmas present. (But I am 99% sure that there is no upgrade fee from any versions of DiamCalc 2.0 to 2.99999).
you can update it here
http://www.octonus.com/oct/download/diam_demo_down.phtml

Oh - and one other thing - you mentioned fire coming from light shining on the pavilion - in my experiance the light that you can see from face up mostly should come from close to parallel to the table or girdle plane - that that comes from the directions you are playing with must come from directly below the stone and in most cases it is pretty black down there.
 

beryl

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Garry:
I wrote this article about a year ago. At that time there was discussion here about light from below the gem, and I think that you mentioned some positive aspects of it; that is why I mentioned it here.
To me the most iinteresting thing was the yellow from white light which had no yellow and the fact that it is visible only a short distance from the gem - as can be observed in the full view with the viewer's head, at right. This may explain this 'phenomenon' to folks who have noticed it and been puzzled.

I play with DiamCalc and Anton's 'Facet Designer' to pass time at the casino; they are both fun and informative and occasionally I find something that I think may be of interest to others. I have already shared such 'handouts' with certain others that I know are interested; I gambled that PriceScope might be interested in this. Recall that there was no response to my article on cutting ovals; since then I have done much more on that but have not shared it here. Perhaps there should be a separate corner of PriceScope for such material so the majority are not bothered but the few can benefit.
 

Garry H (Cut Nut)

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Date: 12/12/2006 6:23:34 AM
Author: beryl
Garry:
I wrote this article about a year ago. At that time there was discussion here about light from below the gem, and I think that you mentioned some positive aspects of it; that is why I mentioned it here.
To me the most iinteresting thing was the yellow from white light which had no yellow and the fact that it is visible only a short distance from the gem - as can be observed in the full view with the viewer''s head, at right. This may explain this ''phenomenon'' to folks who have noticed it and been puzzled.
I play with DiamCalc and Anton''s ''Facet Designer'' to pass time at the casino; they are both fun and informative and occasionally I find something that I think may be of interest to others. Perhaps there should be a separate corner of PriceScope for such material so the majority are not bothered by it.
People can choose to click and open - or not open a link Bruce. Not our problem


http://www.gemology.ru/cut/english/rainbow/4.htm I am sure you read this paper by Anton? You probably translated it for him. there are other aricles that explain why we see different colors at different distances too. It depends on the size of the light source, distance from light, size of pupil and distance from stone to eye, as well as the overall brightness of the background. I have written something with Sergey and Yuri about this but can not post it pre publication in a journal.

I think we were discussing such things in threads on reversability of fire 9you won - I lost and learned) and also one where Michael showed a great firey photo - which I felt was enhanced by fire from pavilion leakage (which Michael denied I think).
 

beryl

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Serg:
As you know, I had wanted to study light, beyond what they taught in school, when I retired. Thanks to you and Anton I can do some of it with your software in my limited spare time (I will never retire).
 

beryl

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Garry:
I did not translate Anton''s article, but rather edited the translation, which was awkward and garbled.
I am aware of Sergey''s work, displayed at the Moscow Conference.
I think that Michael''s famous photo was taken in sunlight filtered through a tree.
 

beryl

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For those of you who want it, I can e-mail a copy of the handout format which is easier to follow because of its juxtaposition of text and illustrations.
 

strmrdr

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Have a question, this is something I was looking into but other stuff came up and my DC broke.

Does the pavilion angle effect the angles at which colored light is returned and which colors?
One of the things I was looking into is the light path of light hitting the mains vs the lower girdles when entering the crown at the same angle.

thoughts?
 

Paul-Antwerp

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Very interesting article, Bruce.

Whenever you write something, we have to re-read it at least twice before grasping it, but it is always extremely interesting.

Live long,
 

JohnQuixote

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Date: 12/12/2006 7:18:57 AM
Author: beryl
For those of you who want it, I can e-mail a copy of the handout format which is easier to follow because of its juxtaposition of text and illustrations.
Thanks for taking the time to do this Bruce. I would enjoy seeing the handout you prepared.
 

beryl

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Strmrdr:
There is no simple answer to your question.
Much has been written about the different reflections of pavilion mains and halves, which differ by about 2°, but this, by itself, has nothing to do with dispersion and fire.
Dispersion and fire have to do mostly with how rays exit a gem (we discussed that here a year ago). Because the colors I have shown here change within about 6° tilt of the gem, it is possible that one color will be separated by the mains while another is separated by the halves. If you read my commentary (addendum to the article) and play with the source colors and intensities, you will observe many fascinating things; this will teach you more than I can with words.
The fractioning effect I describe is only one of many factors affecting color separation = 'fire'. Mike Cowing's famous photo best shows the effect of multiple pinpoint sunlight.
 

:)

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This article was great! Thanks for explaining!
 

strmrdr

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Thanks beryl, I know we had discussed it before and I was curious if your new research had shed any light on it.
 
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