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This is a question that has been bugging me for over 15 years! In high school while studying elements our teacher showed us a clear white rock or element.

It was simply flat on both sides but when placed on a sheet of paper would transfer the letters from the page beneath it to the top surface of the rock.

I remember being amazed by this rock, but could not remember what it was. Now I am working on a creative project and would love to see if I can incorporate the material in my design.

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I used F'x answer as a starting point, and I found the mineral. It's called Ulexite.

The fibers of ulexite act as optical fibers, transmitting light along their lengths by internal reflection. When a piece of ulexite is cut with flat polished faces perpendicular to the orientation of the fibers, a good-quality specimen will display an image of whatever surface is adjacent to its other side (as shown in the photograph).

enter image description here

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I'm not sure I understand what you want from the description above “transfer the letters”, but there is a typical high-school demonstration that I can think of that closely matches this description: that of birefringence.

   enter image description here

Calcite (featured above) was the first material with which this effect was observed, in 1669, and still an easily obtainable material for demonstrating it.

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  • $\begingroup$ Very similar to this. Perhaps my memor is bad. What i remember is the image from the bottom sheet of paper looking like it was on top of the rock. So if the rock is one inch thick and sitting on a newspaper, it would be as if the newspaper was on top of the mineral and not beneath. I think the teacher said they were used for tv screens. Dont remember it having the double effect. $\endgroup$ – Frank May 27 '12 at 1:21
  • $\begingroup$ FX thank you for your answer, helped me find exactly what i was looking for. $\endgroup$ – Frank May 27 '12 at 1:42

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