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UltravioletPhotography

Visible induced IR fluorescence in mineral specimens


Hornblende

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I recently began to do some experiments with minerals and IR light (hopefully with UV soon).

Unfortunately, only a few minerals had an interesting behavior under IR 850nm, such as turquoise turning completely opaque to IR, or very dark chrome tourmaline turning completely transparent!

 

Being inspired by some of the VIIRF thread on the forum I tried to do the same. A lot of minerals are fluorescent under UV light, why not under visible light? And it works! See below.

 

Gear and Procedure :

 

- Zwo ASI 120mms monochrome camera

- Zwo IR 850nm filter

- Iphone led light

- UV/IR cut filter from an old webcam

 

I first taped the UV/IR cut filter over the led light of my iphone to make sure no IR light is shined on the mineral specimens.

Then, with the camera equiped with the IR filter I took 30s pictures at 0 gain to keep the noise low.

 

Here are the two results so far, I'll post more as I go through my collection :

 

 

Jadeite jade : monochrome visible light

post-136-0-34750700-1485659272.jpg

 

Jadeite jade : visible induced infrared fluorescence.

post-136-0-35652800-1485659271.jpg

 

The glowing parts are green in visible, which in jandeite means they are rich in chromium. Minerals rich in chromium are often fluorescent under UV light, now we know they are under visible light.

 

Chromium garnet + Apatite : monochrome visible light. Even at the naked eye these apatites and garnets looks almost the same! Which are the garnet? Which are the apatite? Maybe the fluorescence can separate them??

post-136-0-77684700-1485659270.jpg

 

Chromium garnet + Apatite : visible induced infrared fluorescence.

post-136-0-34399400-1485659273.jpg

 

Annnd.. the apatites are strongly fluorescent in IR under visible light! This is probably because apatites are rich in Neodymium. I tested a glass marble enriched in Nd and it fluoresced strongly in IR.

The garnet however, even being rich in chromium, dont show any sign of fluorescence. Maybe their Iron content inhibits the fluorescence..

 

Visible induced IR fluorescence in minerals is easily observable and safer than UVIVF. I think it could be even used for identification purpose or treatment detection in gemstones.

It could even be possible to shine violet light, cyan light, green light, etc in order to see the difference in IR emission and make a composit image showing "false colors IR fluorescence".

More tests are to come!

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This was quite interesting! Tell me, do you have a filter wheel? I know they make them for astro camera setups. Sounds like it might be handy for doing your false-color VIIRF pics, for instance.
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Thanks Andy!

No I don't have a filter wheel yet. For the moment I tape the filter in front of the CCTV lens. It is a little chaotic but it works :lol:

Do you know what would be awesome? A camera with an IR bayer filters over the sensor in order to have native false color IR images and a correspondance between colors and wavelenghts. Same for UV.

 

Something like 300-330nm filter, 330-360nm filter and 360-400nm filter over the pixels...

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I'm not 100% sure how they make the Bayer, but it might be part of the chip fabrication process (depending on camera) according to wiki, which suggests that many manufacturers make it from photoresist during chip fabrication, rather than as a separate step. Doing "true color IR" would probably be easier than UV, since photoresist has its own interactions with UV -- that's how they cure it! -- aside from the reactions of any dyes. The current Bayer already produces a "true color UV" palette that we all use here, so I assume you mean making the different wavelength-to-color mappings more distinctive.
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The current Bayer already produces a "true color UV" palette that we all use here, so I assume you mean making the different wavelength-to-color mappings more distinctive.

 

Yes, I think I read somewhere that we can't really make a correspondance between UV false color showing up and wavelenght being reflected.

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It seems to be yes-and-no? I think most people accept that the false-yellows are shorter wavelength colors than the false-blues. Whether it can be made more fine-grained than that, I am not sure. This assumes our standard white balance off the accepted materials like PTFE.

 

Edit: whole long discussion back here:

http://www.ultraviol...d__104#entry104

 

But you know, even if the Bayer were improved to make the UV false colors more distinctive (say by adding something that produces a false-red), you still couldn't directly invert the mapping to go from particular wavelengths to particular colors. Same with visible light photos, for that matter.

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I never know how to respond to this! There might be a broad correlation, but nothing you can be 100% sure about. UV recording and its accompanying raw colour is dependent upon so very many variables. Camera sensor, lens, filter, converter, colour spaces, monitor, illumination, time-of-day, altitude, geographic location, camera white point, white balance algorithms and more.

 

That we can standardize the false colours across Bayer-filter platforms is somewhat surprising, so there is something to the correlation. But the standardization is NOT precise. It varies a great deal.

 

Think about it for a second with this example: Yellow light composed of reflected Red+Green versus yellow light as a single wavelength.

 

An example like that tells you that there is a many-to-one relationship between wavelength-to-colour* mappings. So when you see false yellow can you be sure about where it came from?

 

*Perhaps I should say wavelength_combinations-to-colour.

 

Without a spectrometer to confirm the research, we can't really say.

 

ADDED: In attempting to determine a many-to-one wavelength-to-colour mapping, first start with the raw colours before white balance has been adjusted.

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I should have also added this: Do flower petals (for example) only reflect "pure" wavelengths? (How do you refine that question?) Like, could there be an area on a yellow flower petal which is actually reflecting equal amounts of red and green to get that yellow? If not, then the wavelength-to-colour mapping might be valid (subject to all the constraints and approximations which are incurred when we translate from physics to 8-bit colour RGB representation.
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I don't think so, although they probably do reflect predominantly in a narrow band for a particular spot on the petals? The only "pure" wavelengths we ever see come from lasers, pretty much (and even they have a very tiny spread). I am not sure how flowers produce their colors in the first place. How much of what we see is from pigments versus interference phenomena (like on butterfly wings)?
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I think it could be even used for identification purpose or treatment detection in gemstones.

 

See my site http://www.beyondvisible.com/BV1-UVIRLum2006GRC.html

 

You are on the right track. I spent 13 years as a research gemologist at GIA Research in Carlsbad CA. While fluorescence can be a reliable test for some gemstones it requires an enormous reference library of gemstones from different locations before a positive fluorescence ID can be used reliably due to variations in trace element chemistry. In addition, the many and varied gemstone treatments can effect fluorescence reactions.

 

Fluorescence can often be induced by visible wavelengths and is quite noticeable in some gemstones - "Burma" rubies were famed for their spectacular color almost glowing red, and in fact they were, as red fluorescence was induced by the blue component in visible light.

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I have also been trying some minerals with IR luminescence techniques. The image below is of a section through a fossilised Monket Puzzle tree (Triassic). Unfortunately I don't know the different minerals involved in the fossilisation process.

 

In the Kodak book on Applied Infrared Photography (1972. no. M28) there is a good section on IR luminescence. They used the mineral Greenockite as a "standard", but I can't get hold of a piece!

 

My images was shot with a cyan LED torch (LEDWAVE), and 850nm IR filter in a completely dark room.

post-47-0-11801700-1485776913.jpg

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Thanks shane, Your website is very interesting! I am happy to see UV and IR reflected photography can be used for pearl identification/treatment.

In fact I am a FGA gemologist myself. I often use the UV fluorescence test, even if it is not diagnostic I think it is quick to do and can give a lot of infos.

While fluorescence can be a reliable test for some gemstones it requires an enormous reference library of gemstones from different locations before a positive fluorescence ID can be used reliably due to variations in trace element chemistry. In addition, the many and varied gemstone treatments can effect fluorescence reactions.

 

This is why I have in mind to do a DUG in Nante with pr. Emmanuel Fritsch about the practicability of UV and IR photography for gemstones treatment detection/identification.

 

 

Adrian, very nice photo! Strangely the IR paterns doesn't seems to correlate with the visible paterns.

I really need to have one of those Cyan led light

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They used the mineral Greenockite as a "standard", but I can't get hold of a piece!

 

Should be able to buy it on line but better to get pure cadmium sulphide.

 

In fact I am a FGA gemologist myself.

That makes 2 of us.

 

Emmanuel Fritsch

Emmanuel hired me at GIA in 1995, we are old friends but been out of touch for a while.

 

See https://www.gia.edu/gems-gemology/spring-1999-separation-natural-synthetic-colorless-sapphire-elen

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