Lenticular badges

Lenticular printing, which enables the production of images that change according to the angle of view, was invented during the 1940s. Two or more images are sliced and interlaced so that each is visible when looked at through a correctly aligned lenticular plastic lens.

By the mid-1960s this technology was used in the West to produce advertising material and novelty items such as blinking-eye badges; in China it was employed to multiply the number of slogans that could be expressed on a single Mao badge.