Jon Singer (jonsinger) wrote,
Jon Singer

Tenebrescence... a form of photochromism that occurs in a few minerals; the ones I’m aware of are forms of Sodalite. The piece I show here is Hackmanite, which is probably the best known, and was the first type I learned about.

[[I must note that the first and last photos are identical. I don’t have a photo of the piece in its fully bleached condition because I showed the phenomenon to some friends before it occurred to me to write this, and my “Before” photo from this set (which, in any case, is nearly identical to the photo here) is blurred. Grump.]]


Here’s what a piece of Hackmanite looks like when it is mostly bleached, which is its normal condition:

I illuminated the piece with longwave UV (provided by a 4-Watt BLB fluorescent tube) for about 2 minutes. It doesn’t take that long if I put the bulb right on top of the piece, but I wanted to show you the fluorescence, so I moved the lamp a few cm away.

The fluorescence shifts toward the red during the UV exposure, as the sample darkens. It is actually brighter than it appears here; the camera picked up enough UV to dominate the photo.

Here’s what the piece looks like afterward:

This is a nice deep color change; some samples are not as good, some are even better.

It usually takes a while (days to weeks, IIRC) for the color to fade if you leave the sample in the dark or in sunlight; but it occurred to me that I might be able to speed up the process. Here’s what happens when I shine a rather bright white LED flashlight on the sample for a minute or two:


...And here, again, is what it looks like afterward:

Other tenebrescent minerals can exhibit different colors — Tugtupite, for example, at least in the photos I’ve seen, goes to cherry red.
Tags: tenebrescence hackmanite minerals color
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So. Freakin. COOL!
'Tis that. When I first read about Hackmanite I don't recall any photos, so I had to imagine what it was like. Much more recently I went looking for it on eBay, and that's where I got the samples I currently have. It was only last weekend that I tried putting the little blacklight right on top of one of them (which results in better color change than other methods I've used), and then the white LED bleaching notion.

Anyway, glad you like it.
That's awesome. Thanks for sharing these photos and your description of the process with us.
My pleasure; glad you like the posting.

I would be really pleased if I could get a glaze to do something like this. There are a few photochromic glazes, but the color change is fleeting, and nothing like as pronounced as what you get with the Sodalite minerals. I've also had one report of a thermochromic glaze that changes color at temperatures that are reasonable, but haven't seen any confirmation. I do get modest thermochromic effects in a few of my own glazes/materials, but only at well over 100 Celsius, which is rather annoying. (When I make ruby dust [this turns out to be trivially easy] it is mauve to lavender as it comes out of the kiln at about 200 or 250 C, and changes to the expectable pale magenta as it cools.)

Hope to see you in June.


4 years ago

That is amazing. I'd never heard of that.
It really is quite something, and not all that common. I have other fluorescent Sodalite samples, some of which are even from a locality where Hackmanite occurs (and fluoresce about the same orange under LW UV), but do not change color. Go figure.

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Hey. My pleasure; very glad you liked it!
that's pretty cool

Not only is it spiffy, it's relatively cheap; I think I paid 6 or 8 bucks for that chunk. Some of them do go higher, though, and a really good piece of Tugtupite is unaffordium as far as I'm concerned.
Oh, my, that's *gorgeous*.
Yup. Both the fluorescence (I should take another photo with a UV-blocking filter...) and the purple are great; the purple is even richer than the photo that the vendor provided on the eBay auction page.
I'll just repeat what everyone else is saying: very cool. Hot. Warm. Whatever.
I love it when I learn something new like this.
Now I have to get some for a present for my sister-in-law.
There are a few items on eBay that look okay to me, but you need to be careful -- some of the stuff is not particularly tenebrescent.

You are a font of amazing, documented in color.
Eep! It is to blush. In color. ;o)

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;o) Would have been better if I'd thought to try the bleaching thing right off. Oh, well. At least I thought of it at all.

Anyway, a fine party deserves a fine party trick, eh?