Charl
Silver Member
This is likely the oddest artifact I ever found. Very nicely made, colorful, a shame the bit is so beat up. It also behaves oddly. When found in a potato field years ago, it was jet black on the side with all the color. That side was face up in the dirt. Took it home and displayed the other side for a few days. Took it out of the case, turned it over, and the beautiful green coloration was everywhere
Huh??. That side was the same color as the other side when found.
I laid it down with the color side face up, and watched, as over the passage of a few days, the color green vanished!! What the hey?
Finally, a friend explained what my celt was doing:
"I think we’re in the second possibility. “Tenebrescence” - also known as “reversible photochromism” whereby the colour change is the result of sunlight. This effect is the principle behind self-adjusting sunglasses, which darken on exposure to sunlight and also “girly” nail varnishes which change colour in the sun… but the materials used there are synthetic.
There are relatively few natural minerals which are tenebrescent. Some members of the sodalite family (such as hackmanite and tugtupite) exhibit it quite strongly. The colour change is normally from white/colourless to purple-red after exposure. Spodumene (a lithium-rich silicate) also exhibits the property, changing from white/colourless to green. There is a variety of spodumene called hiddenite which is emerald green to begin with, so I would guess that might go even darker green on exposure.
It’s the ultra-violet part of the spectrum that initiates the change and most glass doesn’t let too much of that through, so you may find it takes rather longer to show any effect than would be the case without glass. The phenomenon can be repeated indefinitely, but is normally permanently destroyed by heating.
There are plenty of spodumene sources in your area – it normally occurs in pegmatite rocks"
So, here is my "haunted" celt. I keep the color-side down in the case, so the color won't fade.
Leave it color-side up, and all the green will fade until it looks like the other side of the celt.....
Huh??. That side was the same color as the other side when found.I laid it down with the color side face up, and watched, as over the passage of a few days, the color green vanished!! What the hey?
Finally, a friend explained what my celt was doing:
"I think we’re in the second possibility. “Tenebrescence” - also known as “reversible photochromism” whereby the colour change is the result of sunlight. This effect is the principle behind self-adjusting sunglasses, which darken on exposure to sunlight and also “girly” nail varnishes which change colour in the sun… but the materials used there are synthetic.
There are relatively few natural minerals which are tenebrescent. Some members of the sodalite family (such as hackmanite and tugtupite) exhibit it quite strongly. The colour change is normally from white/colourless to purple-red after exposure. Spodumene (a lithium-rich silicate) also exhibits the property, changing from white/colourless to green. There is a variety of spodumene called hiddenite which is emerald green to begin with, so I would guess that might go even darker green on exposure.
It’s the ultra-violet part of the spectrum that initiates the change and most glass doesn’t let too much of that through, so you may find it takes rather longer to show any effect than would be the case without glass. The phenomenon can be repeated indefinitely, but is normally permanently destroyed by heating.
There are plenty of spodumene sources in your area – it normally occurs in pegmatite rocks"
So, here is my "haunted" celt. I keep the color-side down in the case, so the color won't fade.
Leave it color-side up, and all the green will fade until it looks like the other side of the celt.....
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Wish I could find one of those celts out here.
