In 1948 he co-founded the international artists’ group CoBrA together with Constant, Corneille, Asger Jorn and others. Its members preached that creativity was not the sole privilege of professional artists but could also be found among children and folk artists. Within CoBrA Appel developed an expressive form of painting based on primitive art and children’s drawings. He employed figurative elements but exercised total freedom in his formal language. His sculptures from this period consisted of assemblages.
Around 1965, Appel’s three-dimensional work consisted of painted wooden reliefs and freestanding sculptures. In the 1970s he sculpted animals, figures and heads from stainless steel and glazed ceramics. In the mid-1980s he produced three-dimensional works from wood and rope incorporating Polaroid photographs. From 1989 he made sculptures from objects from various cultures.
Appel was commissioned to produce monumental public works in a variety of media. The best known of these are his wall paintings in the Stedelijk Museum in Amsterdam and in the UNESCO building in Paris and the ceramic wall tiles in the World Forum (Congresgebouw) in The Hague. Appel’s international breakthrough came in the 1950s. Initially his work was poorly received in the Netherlands and in 1950 he decided to leave his native country. He lived in Paris until 1965 and then in Auxerre until 1972. Thereafter he split his time between New York, Tuscany and other homes. Karel Appel died in Zurich on 3 May 2006.