|Glow in the dark paint panel.
This is a clever little toy. It's a picture frame with two pieces of glass mounted about 1/8" apart, with the gap about half filled with europium activated strontium aluminate luminous powder (the kind you use to make glow in the dark paint). The powder does not glow on its own, but if you shine a light on it, it glows for a few minutes. Using a small LED flashlight (blue or UV is best) you can "write" on it in light, just like you can write on walls painted with luminous paint.
But then you get to the clever part: After writing something, or just exposing the whole panel to bright light, you can tip it and make the powder cascade down, taking the luminous portions with it. If you've exposed the whole panel you get interesting patterns that look like rock strata, alternating light and dark. (Only the top surface of powder is exposed, and when you mix it up you get layers of dark and glowing powder.)
I think the source I list is correct, but I've had this thing so long I no longer remember exactly who I got it from. The date listed is the date when it was photographed and added to the collection officially.
Source: eBay seller teddp
Contributor: Theodore Gray
Acquired: 9 May, 2007
Text Updated: 12 May, 2007
Sample Group: Powders