New Mineral Named After GIA’s John Koivula
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 Post subject: Greenish-red, yellow-blue, and the color yellow
PostPosted: Wed Oct 05, 2011 7:28 pm 
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I found this wrirren by Bob Berman..never really thought about it this way

.............."Colors are simply waves of different lengths and the perception of color comes from the mixture of red, blue, and green. Those are lights primary colors. The true colors. They are totally different from the primary colors of paint.

The bright light architecture has plenty of quirks. We see yellow only when we receive an equal dose of green and red light. You would think seeing red and green light would give us the sensation of “greenish-red but no such color exist. Yellow is our “greenish-red” even if it bears no resemblance to either hue.

This contrast with our subjective experiences of sunlight’s other primary colors. We do indeed percieve reddish-blue as purple and greenish-blue as aqua or cyan. Yet thanks to our eye-brain wiring system, we cannot gain the subjective experience of a reddish-green or a yellow-blue, nor even imagine it."......................
Bob Berman

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 Post subject: Re: Greenish-red, yellow-blue, and the color yellow
PostPosted: Wed Oct 05, 2011 11:52 pm 
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Interesting! :-k


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 Post subject: Re: Greenish-red, yellow-blue, and the color yellow
PostPosted: Fri Oct 07, 2011 2:03 pm 
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This was the subject of Brians last chat (The one we couldn't save or copy) That was a real pity because it was something I had never encountered before and was a Fascinating subject. Unlike paint it's colour subtraction rather than colour addition. So if you shine a blue and a yellow light at the same spot on the wall you don't get green...you get white.


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 Post subject: Re: Greenish-red, yellow-blue, and the color yellow
PostPosted: Fri Oct 07, 2011 5:59 pm 
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I was trained as an artist and I have a terrible time trying to reconcile color between fine arts and gemology (not just the names :lol: ). I think maybe it's because of this difference. (Or my eyes... :roll: )

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 Post subject: Re: Greenish-red, yellow-blue, and the color yellow
PostPosted: Sat Oct 08, 2011 7:14 pm 
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In the world of gemstones there are two examples of mixing red and green to make yellow that are quite exciting.

Alexandrite's color change is enhanced because the mixing of it's two colors, as you would see under mixed light conditions, is yellow. Yellow mixed into and dominated by red or green does not produce the continuous color mixture that we perceive when, for example, you would have a color changer from blue to green. I have tourmaline, that I believe to be cuprian, that has a strong shift from blue to green, but much of the time it is blue green because it is difficult to get "pure" white light that isn't mixed in modern homes. I morn the departure of incandescent lights because they can bring out fantastic colors in some tourmaline. Paraiba tourmaline definitely fires up under incandescent.

The other pink/green mixture that I like is in tourmaline. Nigeria has produce quite a bit of this lately. You think you have a tri-color with pink, green and yellow in pastel tones, but you really have only pink and green. As the stone is turned you get to see color change caused by different mixtures of pink and green. It is pretty neat.

Finally like all spectral colors, violet, blue, green, yellow, orange and red, yellow has it's own own set of wavelengths and does not have to come from mixing green and red. It is certainly true that mixing the primary colors, both the set of additive and subtractive, can produce all the colors we can perceive.


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 Post subject: Re: Greenish-red, yellow-blue, and the color yellow
PostPosted: Mon Oct 10, 2011 12:05 am 
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bruce_tourm wrote:
In the world of gemstones there are two examples of mixing red and green to make yellow that are quite exciting.

Alexandrite's color change is enhanced because the mixing of it's two colors, as you would see under mixed light conditions, is yellow.

Don't forget, chrysoberyl is trichroic—red, yellow, and green. The color one sees is also a function of orientation.


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 Post subject: Re: Greenish-red, yellow-blue, and the color yellow
PostPosted: Tue Oct 18, 2011 4:44 pm 
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When you see a good demonstration of metamerism sometimes you can't believe your eyes.

You especially can't believe some light sources like if they have too much blue in them and call themselves white.

Why I suggest people buy xenon arc lamps if they really want to know what color something is under artificial light.


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 Post subject: Re: Greenish-red, yellow-blue, and the color yellow
PostPosted: Wed Oct 19, 2011 10:07 pm 
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I can't add anything to the science, but this discussion reminds me of a comment Tom Stoppard made in one of his plays: “The colours red, blue and green are real. The colour yellow is a mystical experience shared by everybody.” (from Rozencrantz & Guildenstern Are Dead)


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