Imi Knoebel Core Pieces Author:Martin Hentschel, Johannes Stüttgen, Colin Lang German artist Imi Knoebel (born 1940) is celebrated for his minimalist, abstract painting and large-scale sculpture. This exhibition catalogue reviews his earlier works, focusing on the central piece Raum 19 (1968)-a large, wooden environment that references the work of Knoebel's teacher, Joseph Beuys.