Who hasn’t seen them before in the hall of mirrors at the fair: in a mirror with a bent surface you can appear really small, very tall, very fat or very thin. The bent surface of the mirror distorts reality.

But it also works the other way round: a distorting mirror makes crooked things straight again. For example, a teacup with a reflective surface and a matching saucer that is covered with a distorted image. The curved mirror on the cup reflects the picture on the saucer making it appear normal, and it looks as if it were painted on the cup.