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Jack Thurber
Joined: 18 Dec 2009
Posts: 11
Location: Georgia
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 Posted: Dec 13, 2010 04:10 Post subject: Light source dependent color |
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Since I was quite young I have slowly built a modest general collection with some breadth. Recently I decided to dedicate future purchases to a long-planned focus, (though I will still field collect outside of it.) Now I will attempt to buy only minerals that have marked color change, compared to the general environment, with changes in light spectra. It seems my choice of specialty is more limiting than some others. Hopefully this will be good for the collection though. I suspect that I will make fewer purchases, and will therefore more easily be able to acquire higher quality items.
(Aside from fluorescents) I start off only with specimens of Olmiite, Monazite-Ce from Siglo XX, and a Rogerley Fluorite. I admit I may have something else that fits without being aware of it.
At any rate, I was wondering if there were any favorite minerals of this kind that anyone would like to mention. There are a couple of things I have in mind but I have a lot of research to do. By the way, is there a term for this property? I'm interested in knowing about other collections like this that might be out there, in case any come to mind. …and of course anything else anyone might want to share.
Eventually I will build a new case to elegantly and effectively show off the specimens. Perhaps fiber optics could help to keep things simple as far as the display.
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James Catmur
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Location: Cambridge
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| Posted: Dec 13, 2010 04:43 Post subject: Re: light source dependent color |
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Jack
If you are looking for some really good LED lighting (instead of fibre optic) I can recommend the following source. I have recently fitted my cabinets and they look superb
https://www.lowestone.com/acatalog/LED_LIGHTING.html
They are not cheap but that are far better than anything else I can find on the market
James
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Jordi Fabre
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Joined: 07 Aug 2006
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Pete Richards
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| Posted: Dec 13, 2010 08:51 Post subject: Re: Light source dependent color |
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A number of cerium-bearing minerals show this property. Ancylite-Ce and burbankite from Mont Saint-Hilaire are good examples. They are pink or orange under a halogen light but colorless or greenish under standard fluorescent lights. These color changes are a direct response to the light source, and shift instantly when the light source changes.
Some sodalite from Mont Saint-Hilaire turns deep pink when exposed to long-wave ultraviolet light, but bleaches to white under a halogen light. This color shift is a change in the chemistry of mineral itself, in the sense that it persists for some time after the light source is removed, but the change occurs in seconds to less than a minute when exposed to the right strong source of light.
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Collecting and studying crystals with interesting habits, twinning, and epitaxy |
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alfredo
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Joined: 30 Jan 2008
Posts: 979
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| Posted: Dec 13, 2010 10:05 Post subject: Re: Light source dependent color |
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Today at the Tokyo show I saw a kyanite that changed between deep blue and a lighter green depending on whether it was illuminated by incandescent or fluorescent lights! Alexandrite is probably historically the most famous colour-changing mineral variety. Neodymium-bearing minerals commonly show a pink-green colour change, like the Siglo XX monazite-(Ce) you already have. A lot of minerals whose green colour is due to iron, like ludlamite and boracite, will look a lovely green under incandescent lights and a sickly greyish green under fluorescent tubes.
A twist on this topic is that I have often used minerals to demonstrate to people that the folk selling energy-efficient compact fluorescent bulbs are liars if they make claims using the words "daylight", "sunlight", "full spectrum", "continuous spectrum", or variations on that theme. The fact that my ludlamites look so damn ugly under those bulbs is proof that they produce nothing resembling a "full spectrum" or sunlight! Some minerals, on the other hand, look much brighter under those lights. I think they should be banned from mineral shows, for being misleading, except for people like Jack using them to demonstrate colour change.
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Elise
Joined: 22 Dec 2009
Posts: 243
Location: New York State
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| Posted: Dec 13, 2010 12:49 Post subject: Re: Light source dependent color |
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| alfredo wrote: | | Today at the Tokyo show I saw a kyanite that changed between deep blue and a lighter green depending on whether it was illuminated by incandescent or fluorescent lights! |
It would be neat if you get a chance to look at it again to see if it changes also with direction and with a polarizing filter. My understanding is that the color-change seen in blue kyanite from Kenya is due to chromium in the near absence of vanadium and in one direction the color can go from light green in daylight to purplish in incandescent; the mixed effect of pleochroism and color-change due to the light source. Gamma and beta rays are bluish green of different intensities and alpha is the weakest, but is the one showing the color change (that is, the color change is caused by one vibration only). In combination without separating the colors with the filter, maybe one would see something like you did today as an overall effect, or maybe you would be surprised if you turned it and saw a much more dramatic color-change while using different light sources. Wish I was there...
Have fun,
Elise
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Jack Thurber
Joined: 18 Dec 2009
Posts: 11
Location: Georgia
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| Posted: Dec 13, 2010 14:56 Post subject: Re: Light source dependent color |
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First of all, thanks so much for the information, especially the tips on the minerals and the causes of the changes in them. The Mont Saint-Hilaire location has interested me for some time and now I have something to look into further. I can't help but wonder if Alfredo does what I do when shopping for cloths and takes them to the window or outside to see how the colors look in daylight. Actually that seems unlikely somehow.
When I mentioned fibre optics I simply meant that I might use the material to transmit light from various sources. I should have been clear about this as I'm not looking to buy a fibre optic lighting system. At this point I haven't looked into what type of filtering the material might demonstrate. (I was already quite interested in that particular LED lighting system actually.)
I will have some playing around to do to attempt to make the effects more dramatic. In the past I've tinkered with making light that's basically perceived as white generally more colorific by reducing the range of wavelengths that make it up. I love my optical supply catalogs and if I'm not careful the lighting could quite easily take the lions share of the cost of the endeavor. When it comes time to construct the cabinet I will need to consult with experts.
Kurt Nassau's book "The Physics and Chemistry Of Color" should help my project quite a bit but has been sitting on my shelf for a year. It may take some dedication for me to get through as I'm not a scientist. (I have studied the science of color but not in a comprehensive or systematic way.) At times I get excited and wander into unknown terrain without packing properly. When I attempted Dana's textbook I discovered that I need to take some more advanced math classes before trying again.
More direct observation is one thing for which I need to take the time too. Anyway, I apologize for the long rambling nature of my posting. Thanks again to all.
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Elise
Joined: 22 Dec 2009
Posts: 243
Location: New York State
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| Posted: Dec 13, 2010 16:28 Post subject: Re: Light source dependent color |
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| Jack Thurber wrote: | | Kurt Nassau's book "The Physics and Chemistry Of Color" should help my project quite a bit but has been sitting on my shelf for a year. |
You might like the condensed version on just minerals which he wrote for American Mineralogist and which is published on the AmMin website (1978) The origins of color in minerals Volume 63, pages 219-229:
https://www.minsocam.org/msa/collectors_corner/arc/color.htm
(link normalized by FMF)
He also published a similar version in several installments of Lapidary Journal in 1975 which is in an even more readable form (I picked up the 4 issues on eBay for just a few dollars, the last one has corrections to the 3 part series): Nassau, K. (1975) The origins of color in minerals and gems. Lapidary J., 29, pp. 920-8, pp. 1060-70, pp. 1250-8, p. 1521. They really are very good summaries and, along with the book, are a basis for understanding color, but they really don't go into all the color change mechanisms out there....for that I can recommend a mountain of papers which is ever growing.... I can say it is a really complicated subject to study, especially when several mechanisms are working in concert!
Best wishes,
Elise
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Elise
Joined: 22 Dec 2009
Posts: 243
Location: New York State
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| Posted: Feb 26, 2011 10:20 Post subject: Re: Light source dependent color |
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The link above ties in more information on the LEDs; I was hoping also that this current thread would tie together with the discussion on caring for light sensitive minerals with its updates on the Frank Howie book: https://www.mineral-forum.com/message-board/viewtopic.php?p=9759&highlight=#9759
| alfredo wrote: | | A twist on this topic is that I have often used minerals to demonstrate to people that the folk selling energy-efficient compact fluorescent bulbs are liars if they make claims using the words "daylight", "sunlight", "full spectrum", "continuous spectrum", or variations on that theme. The fact that my ludlamites look so damn ugly under those bulbs is proof that they produce nothing resembling a "full spectrum" or sunlight! Some minerals, on the other hand, look much brighter under those lights. I think they should be banned from mineral shows, for being misleading, except for people like Jack using them to demonstrate colour change. |
At one of the conferences I participated in at Tucson, there was a very interesting presentation on daylight equivalent lighting, including OttLights and others which are used in color-grading gemstones. Since subtle variations in color, or lack of color, translate into huge differences in pricing in the gem world, the topic is very hot within in that industry. The presentation showed spectrums of many brands of fluorescent lights which illustrated just what Alfredo points out. During my two weeks at the Tucson shows, I spent as much time looking at dealer's cases and lighting as I did admiring the mineral specimens within (I also walk around with my own arsenal of flashlights).
Yesterday I met with a lighting specialist and electrician to go over plans for installing new lighting in existing display cases housing a variety of specimens. These were very knowledgeable people who have done work in some well-known museums, but admittedly not for mineral displays. As a demonstration, I brought out a chunk of kunzite spodumene and a faceted color-change glass (whose color almost exactly matched the kunzite) and put various lights over the materials to demonstrate what happens (color shifted and under the OSRAM fluorescent light, the glass changed to blue).
I was very impressed with the LED light strips which are available in a range of temperatures. I really had no idea how fast the technology has progressed in recent years and was happy to go home with a sample 3000K strip to play with (they are getting me 3500 K and higher samples). What surprised me was what the LED strip did to the OSRAM light tube with the latter turned off (bottom photo) - what are the implications for sensitive minerals? We are contemplating a mixture of lighting - LED strips retrofitted to case shelving with fluorescent lights in top of that case; halogens inside another large case with ventilation, and halogen spots on ceiling tracks for a case which can not be retrofitted with internal lights (here we also grapple with reflections).
Another aspect we are dealing with is a new coating on inside of the case glass which only transmits 88% of the light while cutting down UV to almost zero. Kunzites and fluorites which have been in the case for 25 years have faded to pale versions of their former selves; going forward I hope to mitigate that while still displaying what is within to its best advantage possible given a compromise of many variables.
Hoping this might also be apropos to the discussion on mineral museums: https://www.mineral-forum.com/message-board/viewtopic.php?t=1580
Cheers!
Elise
| Description: |
Kunzite spodumene crystal shards (Oceanview mine, CA) and faceted color-change glass. Top: winter overcast daylight; middle: 3000K LED strip; bottom: OSRAM Fluorescent ?K (transmitted), glass changes to blue.
(photo: Elise Skalwold) |
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The same group with the OSRAM fluorescent light turned off and the 3000K LED strip shining on it; the OSRAM's tubes are glowing, but not enough to change the color of the glass to blue.
(photo: Elise Skalwold) |
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Elise Skalwold |
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