Graphic designer Karel Martens is recognized for his experimental Dutch modernist style, which is marked by clean Swiss typography, repetitive geometric shapes, and static forms. He started working in graphic design before it was considered an independent field, and got his start as a designer of book covers for the socialist publishing house Socialistiese Uitgeverij Nijmegen (SUN). Martens is best known for his series of Dutch PTT phone cards, which feature a rainbow of faded, overlapping numbers that represent a coded version of the Dutch national anthem. Fascinated by optical illusions, Martens produced a series of monoprints by deliberately misusing a letterpress to create experimental, one-of-a-kind images. The monoprints are inspired by the aesthetics of the artists’ group ZERO, and display a more innovative side of Martens’s signature minimal designs.