How does an Etch A Sketch work?
This popular child’s toy works by encasing a clear glass or plastic screen within a plastic housing, that itself is filled with a large quantity of aluminium powder and tiny ball bearings. This powder sticks to the screen – evenly spaced by the ball bearings – and generates the greyed slate, upon which patterns can be drawn. The drawing mechanism is activated by two circular dials, positioned in the bottom-left and right corners of the plastic frame. These are attached to a stylus via a pair of orthogonal rails, which when turned cause the stylus to draw lines in the aluminum powder. This action, when viewed form outside the Etch A Sketch, appears as if black lines are being drawn on the grey slate. in fact, however, the stylus is merely exposing the darkened interior of the plastic casing to the human eye. Naturally, when the device is turned upside down or shaken, the aluminium powder re-coats the clear screen, destroying the previous carved lines and presenting a clean slate.