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

Through the doors, women working as outsourced workers for existing nearby factories can be seen putting handles on plastic bags and metal springs together.

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When Jerrold Zacharias was developing the first atomic clock, working in Building 20, he removed two floors in his lab to make room for a three-story metal cylinder.

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