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 Post subject: Metamerism
PostPosted: Fri May 04, 2007 1:15 am 
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I would like to see some information on metamerism in GP and how it relates to what we are currently referring to color shift in the trade.
I think that an amethyst frequently exhibits metamerism, but a sapphire that changes from purple to blue is color changing.

But this is my personal opinion.

A couple of links on metamerism when used in fashion or web design:

http://www.wisegeek.com/what-is-metamerism.htm

http://www.colormatters.com/des_meta.html

Kurt Nassau touches on it briefly in The Physics and Chemistry of Color in reference to mineralogy.


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PostPosted: Fri May 04, 2007 12:06 pm 
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Hi,

I'm not going to burn myself on that one.
Maybe they are both metamerism effects?

Doos
(Pseudo-Scientist of The gemology Project)


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PostPosted: Fri May 04, 2007 4:29 pm 
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More to ponder: http://www.colorvision.ch/tutorials/lesson05.php

Good luck in this debate. :lol:


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PostPosted: Fri May 04, 2007 6:03 pm 
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Remember these?
Image
Image

The top is an amethyst.
The bottom a rhodolite garnet.
The left pictures were taken with a fluorescent Ott Lite.
The right pictures with a pen light only.
No photoshop tricks, cropping only.

I don't think it's drastic enough to call it a color change. There is enough difference to call it something, but what? Does it define metamerism? Metamerism seems to imply a definite change as to how we perceive color under differing conditions. It doesn't seem to imply a "drastic" change of hue though.
With metamerism they seem to always imply a difference between "TWO identical" items that appear differently under 2 different light sources. Of course no 2 gemstones are exactly the same chemically in their respective breakdowns even if they appear very similar (color wise) under one particular light source. Maybe that's why some stones "shift" and some stones of the same variety and color don't.
Or maybe they all do to a varying degree. Could internal structural differences play a part like twinning or some other variance that might effect how light and it's return is perceived under different light sources?

I have no idea. Just throwing a bunch of stuff out there to further confuse the subject. :twisted:
BTW: Spell check needs an upgrade. It's never heard of half these words. :lol:


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PostPosted: Sun May 06, 2007 1:43 pm 
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JB wrote:

I don't think it's drastic enough to call it a color change. There is enough difference to call it something, but what?



'Night Stones' :? - the colors appear to be turned quite a bit more appealing by incandescent light. Especially the garnet.


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