Magnetic Field Paper

From Coolest Gadgets:

As a kid I remember tapping iron filings on a piece of paper held over a magnet to see the magnetic field, this special magnetic field paper does the same job without the need of the filings. Developed back in the 1970s, with ideas that it might become a replacement for paper, this paper makes magnetic fields visible. Any other magnet can be used, and the paper will allow to to make the magnetic field visible.

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