Lichtenstein extended his source material to art history, including the work of Claude Monet and Pablo Picasso, and experimented with three-dimensional works. During a trip to Los Angeles in 1978, Lichtenstein became fascinated by lawyer Robert Gore Rifkind’s collection of German Expressionist prints and illustrated books, and in 1980 began exploring the Expressionist stylistic vocabulary in paintings such as The White Tree, which evokes the lyricism of Der Blaue Reiter landscapes, and Expressionist Head that mimics Erich Heckel’s 1919 woodcut, Portrait of a Man. Lichtenstein also created a number of small pencil drawings that he used as templates for woodcuts, a medium favoured by Emile Nolde and Max Pechstein among other Expressionist artists. The culmination of this exploration was the Expressionist Woodcut Series, 1980. This set of seven woodcuts includes motifs that echo the Expressionist masterpieces, such as Dr. Waldmann, which recalls Otto Dix’s Dr. Mayer-Hermann, 1926, and Reclining Nude: an addition to Lichtenstein’s repertoire of iconography that had hitherto excluded nude figures. Lichtenstein’s use of appropriated imagery has influenced artists such as Richard Prince, Jeff Koons and Raymond Pettibon.