Op Art for Dummies: Marcel Duchamp's Rotoreliefs

In the 1930s, Marcel Duchamp created a set of 12 Op-Art Rotoreliefs. When placed on a gramophone and spun, they create the illusion of depth. You can see more from the series here. In addition, here is a PDF of the full set, suitable for color printing. Cut them out, put them on a turntable at 33 rpm, and look at them with one eye closed to get the Op Art effect Duchamp intended.