“The technology behind this children’s toy is both simple and complex. Simple, in that an internal stylus is used, manipulated by turning horizontal and vertical knobs to ‘etch a sketch’ onto a glass window coated with aluminum powder. Complex, because the Etch a Sketch employs a fairly sophisticated pulley system that operates the orthogonal rails that move the stylus around when the knobs are turned…”
Read the rest here, and view a gallery of images here. As a child, I was fascinated by the silver powder inside of Etch-a-Sketchs.