why red spinel changes colour under different light?

[pajero_exceed]

Hi, I've got a beautiful red spinel, don't know the origin. The stone displays blood red under sunlight, while shows really dark tone under incandescent and fluorescent light，looks like the colour changes to a bit purplish or brownish red. Can anybody tell me the reason? Is it very common for red spinel? Cheers a lot.

 

[chrono]

I cannot explain the reason why but I know that this is common. I shy away from red spinels that become dark and brownish under incandescent and fluorescent lights, which means a longer and more difficult search for the right red spinel. I was told long ago that the browning or muddiness is caused by the iron content.

 

[pregcurious]

Yes, it is common to find red spinels that look brownish under some lights.

Red and pink spinels often have red fluorescence that makes them appear more bright red under UV light. I posted a picture of my red and pink spinels under a shortwave light source here:

[URL='https://www.pricescope.com/community/threads/pics-of-my-3-favorite-stones.202360/#post-3696598?hilit=uv#p3696598']https://www.pricescope.com/community/threads/pics-of-my-3-favorite-stones.202360/#post-3696598?hilit=uv#p3696598[/URL]

This red fluorescence is prized in red stones, and one should look for it in red spinels and rubies before buying. Top red spinels and rubies, however, should look attractive in all light sources, and not have a strong brown tone. (They should not be mistaken for red garnet.)

I have read that some red spinels become dark under sunlight because they have no or weak fluorescence. I have also heard of stones that get much darker under non-UV light sources, like the stone you are describing. I think some people refer to this as blacking out because it can make the stone look extinct.

It can be difficult to find a stone with medium to medium-dark saturation and tone that performs well in all light conditions. I find reds especially tricky because they can go brown. A nice pink sapphire or spinel is more straight forward to me than buying a red ruby or spinel, at least in terms of making sure that the stone performs well under different lights. I also find cooler colors like blue easier to shop for because they tend to go grey, which seems more attractive than brown (to me).

 

[iLander]

Everything changes color in different lights. Everything!

Just look at paint on your walls some night. The areas where the light hits, will be brighter. I know it seems simplistic, but once you come to terms with that, colored stones will be easier to deal with.

 

[pajero_exceed]

thank you very much for your replies. I think it might be the iron content。 I know it's normal for a gemstone to display different colors under different light, but spinels seem to change more than rubies. I heard that red in rubies is caused by chromium while red in some most spinels is caused by magnesium.

 

[Marlow]

no- magnesium is part of the formula of spinel

Corundum is Al2O3 - pure corundum is colorless

Spinel is Al2MgO4 - so Al2O3 + MgO - pure spinel is colorless too!

Chrome is resp. for red in both - ruby/pink sapphire and pink/red spinel. And responsible for fluorescensce. Iron destroys fluor.

The change or shift of color is course by the light source - look in a mirror in a room with ugly halogen or in a room full of light of a warm evening sun.

iLander is aboutly right!

 

[pregcurious]

The well known and respected Richard Hughes touches on both issues of light changing the color of a stone, and also red fluor changing the appearance of red stones:
http://www.ruby-sapphire.com/r-s-bk-quality.htm

Yes, iron quenches fluorescence.
http://www.ruby-sapphire.com/ruby_connoisseurship.htm

 

[GliderPoss]

Yes mine does this too - in the sun and certain lighting it is pure traffic light ruby red but in others it definitely goes slightly more "oxblood brownish" bleh... I guess that's the joy of gemstones


This one isnt mine (it's it's TWIN! ) but shows what it looks like in sunlight.

This is mine indoors in shade (looks a tad orange for some weird reason but definitely not IRL)

 

[chrono]

Almost all gemstones will change colouration depending on the light source but I think the question here is why some red spinels hold their colour better and why some change so drastically.

 

[Michael_E]

Almost all gemstones will change colouration depending on the light source but I think the question here is why some red spinels hold their colour better and why some change so drastically.

The reason is that there are NO stones which change color other than those which are fluorescent. Gem crystals merely transmit certain colors and if those colors are not in the light source, then they can't transmit them to your eyes. If a spinel transmits mostly red with a little green and blue and the light source has little red and lots of green, then the stone will look like a mix of red and green, also known as brown. Check out this site for some neat transmission spectral images of different gems:
http://www.gemlab.co.uk/

 

[chrono]

The reason is that there are NO stones which change color other than those which are fluorescent. Gem crystals merely transmit certain colors and if those colors are not in the light source, then they can't transmit them to your eyes. If a spinel transmits mostly red with a little green and blue and the light source has little red and lots of green, then the stone will look like a mix of red and green, also known as brown. Check out this site for some neat transmission spectral images of different gems:
http://www.gemlab.co.uk/

Let me see if I understand what you mean (and the link too). So if I want a red spinel (or whatever gem type) that looks great under sunlight, incandescent and fluorescent light, I must select a particular spinel that has very specific amounts of modifiers? I have seen red spinels that brown out under incandescent light and some that stay red. I do not recall whether they react to UV or do not.

What colours does incandescent light bulbs transmit? Lots of yellow? Does this mean that orange or flame spinels will look brown under incandescent light so for it to stay red, one has to look for a red spinel with a purple modifier? Or are you saying that only red spinels with fluroescence hold their red under incandescent lighting?

 

[Marlow]

Chrono - to many questions!!!

Michael - interesting page - but I need time to understand everything.

Think I need the Hanneman Filter set!

 

[Michael_E]

Let me see if I understand what you mean (and the link too). So if I want a red spinel (or whatever gem type) that looks great under sunlight, incandescent and fluorescent light, I must select a particular spinel that has very specific amounts of modifiers? I have seen red spinels that brown out under incandescent light and some that stay red. I do not recall whether they react to UV or do not.

What colours does incandescent light bulbs transmit? Lots of yellow? Does this mean that orange or flame spinels will look brown under incandescent light so for it to stay red, one has to look for a red spinel with a purple modifier? Or are you saying that only red spinels with fluroescence hold their red under incandescent lighting?

Looking for specific colors as modifiers in a stone doesn't work very well since you also would need to be looking for them with a specific light source. If you search for "emission spectra incandescent" you'll see that incandescent light sources have a range of colors and intensities in those colors, so the answer depends on which incandescent light source you're talking about. It's pretty complicated since there are three things going on:

1. The light source has a particular color mix and intensity in those colors. Then you can have reflected light from walls and other items in the environment, which all absorb or reflect parts of that light from the light source, so the light reaching the gem will be partly from the light source and partly from the environment.
2. The gem is like a fancy filter which only lets certain colors through the crystal. Any colors from the light source that are allowed through the crystal are what you see. If the intensity in one transmitted color is a lot greater than the others then you'll see that color. That's why some stones "change color"...the light going through them is mostly in a color and at a high intensity. Take a red/green alexandrite, it transmits in both green and red. If the light source is mostly green, you see that green, if mostly red, then that's what you'll see.
3. The we have the human eye, which changes a little bit depending on who's eye's they are. Some people can see green and red very well and some see those colors as shades of gray. Where your personal sensitivities lie determine what you see.

Searching on "Emission spectra", "transmission spectra" and "absorption spectra" will give you plenty of neat colored images of how different materials react to light. If you were to overlay emission and transmission spectra's and black out everything else you would get a good idea of what colors you would see in a gem. I think that would actually be the best way to talk about color if you really wanted to know what color a gem was, since the light is standardized and everyone is talking about the same thing. Of course this would lead everyone on P.S. to a degree in Physics and that would be fun as well...right?

 

[chrono]

Searching on "Emission spectra", "transmission spectra" and "absorption spectra" will give you plenty of neat colored images of how different materials react to light. If you were to overlay emission and transmission spectra's and black out everything else you would get a good idea of what colors you would see in a gem. I think that would actually be the best way to talk about color if you really wanted to know what color a gem was, since the light is standardized and everyone is talking about the same thing. Of course this would lead everyone on P.S. to a degree in Physics and that would be fun as well...right?

Interesting and if only there is an easy way to do this. Hey, why can't we all have a degree in Physics? Physics is fun, especially when studying light waves/emission.

 

[T L]

Searching on "Emission spectra", "transmission spectra" and "absorption spectra" will give you plenty of neat colored images of how different materials react to light. If you were to overlay emission and transmission spectra's and black out everything else you would get a good idea of what colors you would see in a gem. I think that would actually be the best way to talk about color if you really wanted to know what color a gem was, since the light is standardized and everyone is talking about the same thing. Of course this would lead everyone on P.S. to a degree in Physics and that would be fun as well...right?

Interesting and if only there is an easy way to do this. Hey, why can't we all have a degree in Physics? Physics is fun, especially when studying light waves/emission.

There was a physicist that posted on this board a long time ago. He got into some really interesting discussions.

I love physics btw. When you think about it, visible light is a teeny tiny part of the electromagnetic spectrum. Our gems would look vastly different to a bee for example, that sees in the UV part of the spectrum. It's also fascinating because certain chemical elements are the source of color in a gem, but that's another topic.