Mr Cassagnes saw the potential for the toy when he noticed, while working with metal powders, that marks in a coating of aluminium powder could be seen from the other side of a translucent plate.

BBC: Etch A Sketch inventor Andre Cassagnes dies at 86

One Saturday evening in early 2001 Rabinowitz mixed the drug with a solvent, transforming the mound of powder into a film 1 micron thick (that's a thousandth of a millimeter) coating a piece of foil.

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