Art Catalogue for the Quittenbaum Gallery. Rudolf Kämmer has been one of the most important representatives of concrete art and op art since the 1960s. He is interested in the laws of visual perception, the active observer is always a participant in the creative process. These ideas can be found in the visual and haptic implementation of Studio Umlaut's catalog, which was created on the occasion of an overall exhibition of his work in the quittenbaum gallery.