Magna Doodle is a magnetic drawing toy, consisting of a drawing board, a magnetic stylus, and a few magnet shapes. Invented in 1974, over forty million units have been sold to date worldwide, under several brands, product names and variations. The key element of the toy is the magnetophoretic display panel, filled with a thick, opaque white liquid containing tiny dark magnetic particles. These particles can be drawn to the drawing surface by a magnet-tipped stylus or optionally-provided shapes, or removed to the hidden back side by a sliding eraser bar. The middle layer is divided into a honeycomb of cells, keeping the liquid static and the particles evenly distributed across the panel. The liquid is formulated so that the floating particles can be pulled through it in response to the magnetic forces, but not due to gravity.
Contributions by MarjorieCook, Mr.bonus, and 126.96.36.199.