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 Post subject: Gems' colors and types of lights
PostPosted: Mon Jan 09, 2017 9:35 am 
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Sometimes the more you try to understand things, the more you get confused.
So far I had always stuck to simple opinions like : blue stones like sapphires look better in daylight because there are more blue wavelengths in daylight and sapphires transmit more these wavelengths, red stones like rubies look better under incandescent light because there are more yellow to red wavelengths and rubies transmit more red wavelengths (fluorescence apart).
But things don't seem to be that easy, and according to sources I read different things - sometimes contradictory - and I find it hard to extract general rules.
For instance I read that :
- blue stones might look better under a yellowish light because the yellow, as a complementary color, sets off the blue better
- As a reverse, yellow stones look better under daylight, for the same reason
- Kashmir sapphires maintain their blue intact under incandescent light, which sapphires of other origines cannot do (why should that be ?)
- Heated sapphires look dull under incandescent light, which untreated sapphires don't do (why should that be ?)
- Under daylight only, some stones look better in early morning and late afternoon, some look better in midmorning and midafternoon, some look better at noon, because of the evolution of light along the day
- Garnets, or tourmalines, no matter their color, are always better under daylight than under electric light (why should that be ?)
- ...

So to sum it up and help make the light on this question (no pun on words meant), could you tell me, according to your knowledge and experience, if there are general rules that could define :
- what colors of stones look better under what kind of light
- what families of stones look better under what kind of light
- if there is a general relation between the chromogen agent and the type of light which suits the stone better. E.g, chromium makes emerald green, does emerald look better under incandescent light for this reason, or under daylight because of its blue component ?

Thank you !


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 Post subject: Re: Gems' colors and types of lights
PostPosted: Wed Jan 11, 2017 3:32 am 
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Interesting question...

I notice that my Mahenge spinel with an exc. neon pink get a brownish hint while my cobalt spinel ( Sri Lanka and Vietnam ) look better using LED light.

To be continued....

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 Post subject: Re: Gems' colors and types of lights
PostPosted: Wed Jan 11, 2017 10:39 am 
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Yes, interesting question, I am a bit disappointed not to get more reactions ar answers. Maybe I should have put it in the Colored Stones section, it might have been more widely read.


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 Post subject: Re: Gems' colors and types of lights
PostPosted: Wed Jan 11, 2017 1:31 pm 
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Hi Isi.
I think these questions could all be answered with some experimentation.
-I have never seen a BLUE sapphire look better under any light other than daylight or a daylight bulb.
-I think if we take a sapphire and look at it with a sodium light, we will not be impressed.
And, actually orange is the compliment to blue.
-Yellowish stones look best under incandescent light in my experience. Just take a yellow stone outside. Report back. Do you see an improvement?
-Light changes constantly. The colors we perceive in everything around us changes slightly. This has long been a concern in the textile industry. See metamerism.

-A sapphire can not maintain it's blue color if there is no blue component of the spectrum in the light source. They will ink out.

I remember, years ago on Pricescope, there was a lot of talk claiming the finest colored gems are those that retain the same color when viewed under any light source. This would defy the laws of physics, no?


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 Post subject: Re: Gems' colors and types of lights
PostPosted: Wed Jan 11, 2017 5:35 pm 
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Barbra Voltaire wrote:
This has long been a concern in the textile industry. See metamerism.

As a side note, I've never considered this issue (I'm very far from being a fashion fan, or anything related :) ) before you cited it, some time ago. At the same time, by coincidence, I bought a green micro-fleece sweater online. I opened the package in my kitchen, and... "Hey! This thing is BROWN! They sent me a wrong one, those #@&%". After trashing the envelope, I moved in the living room, I took another look: GREEN. The change is quite evident.
I don't know if I've never realized it in the past, but now I sure own a color-change sweater. :lol:


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 Post subject: Re: Gems' colors and types of lights
PostPosted: Wed Jan 11, 2017 5:54 pm 
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Yellow spodumene goes from "eh..." under normal lighting to "EH!" under fluorescent lighting pretty universally, and (real Cr-bearing) hiddenite sees a similar boost. But I don't think that's a universal property of all yellow stones, just something particular about yellow spodumene.

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 Post subject: Re: Gems' colors and types of lights
PostPosted: Wed Jan 11, 2017 6:06 pm 
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So, in your opinion, Kashmir sapphires retaining better their blue under incandescent light, or heated sapphires becoming duller than unheated ones under incandescent light, is sheer fancy ?


Last edited by Isi on Wed Jan 11, 2017 6:09 pm, edited 1 time in total.

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 Post subject: Re: Gems' colors and types of lights
PostPosted: Wed Jan 11, 2017 6:07 pm 
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Barbra Voltaire wrote:
I remember, years ago on Pricescope, there was a lot of talk claiming the finest colored gems are those that retain the same color when viewed under any light source. This would defy the laws of physics, no?


Maybe a Cr-based ruby comes close to this characteristic? Shine red light on it and it will transmit the red light. Shine green or blue light on it and it will absorb those colors and fluoresce red.


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 Post subject: Re: Gems' colors and types of lights
PostPosted: Wed Jan 11, 2017 6:30 pm 
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I remember that Polaroid did some very interesting experiments on how the eye perceives color. It is *not* what you might think - based on amplitude. It is based on differentials in amplitude. As a result, the human eye is pretty hard to fool. It also makes most simple discussions on how different lights affect color wrong.


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 Post subject: Re: Gems' colors and types of lights
PostPosted: Wed Jan 11, 2017 8:34 pm 
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Isi wrote:
So, in your opinion, Kashmir sapphires retaining better their blue under incandescent light, or heated sapphires becoming duller than unheated ones under incandescent light, is sheer fancy ?


I believe it is very unlikely. Remember all Kashmir sapphires are not the same. From the sapphires I own, I have observed that the blues black out with candlelight.

We are smart gemmos, as I mentioned a walk about could answer our questions.

Stephen wrote:
Yellow spodumene goes from "eh..." under normal lighting to "EH!" under fluorescent lighting pretty universally
Spodumene is an out of this world mineral. I bet that improvement of color has something to do with the it's fluorescent, luminescent and tenebrescent qualities.

Just because this is an interesting paper, I'll post it:
[pdfview]http://www.minsocam.org/ammin/AM38/AM38_919.pdf[/pdfview]

Brian wrote:
Maybe a Cr-based ruby comes close to this characteristic? Shine red light on it and it will transmit the red light. Shine green or blue light on it and it will absorb those colors and fluoresce red.

Makes sense, I'll have to do a walk about with a ruby.


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 Post subject: Re: Gems' colors and types of lights
PostPosted: Thu Jan 12, 2017 9:16 am 
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For sure, observation and experience are paramount, but in this case I was trying to understand if there were general physical rules to sustain them.
Especially since the sources where I read about Kashmir and heated sapphires under incandescent lights seem to come from smart gemmos too ! :wink:

I am especially puzzled by this question of complementary color lighting in relations to stones. For instance, diamond graders use daylight color bulbs to grade the color of a diamond because the blue light shows off better the possible yellow tints. So, would a yellow stone appear more yellow under yellow light or blue light ? Oh well, maybe the blue light enhances more the yellow hue, but maybe the yellow light makes it look better. Maybe these 2 notions are different.


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 Post subject: Re: Gems' colors and types of lights
PostPosted: Thu Jan 12, 2017 5:51 pm 
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I agree with Barbra that blue Sapphire looks best in daylight. Kashmir Sapphire I have only seen in halogen light and only one stone was outstanding ( 2ct gorgous - sleepy colour - to die for - "only" 45K ) . Another stone looked similar to high quality stones from Burma, Sri Lanka or Madagascar. Was from Sera Gems/New York.

Another daylight gem is Chrysoberyl imo.

Esp. if there is a green amount ( Vanadium and Chrome - not enough for Alexandrite ) in the color ( neon greenish yellow, green and bluish green) they look best in daylight.

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