In the 1970s and 1980s, he gained fame with his interpretation of urban walls in his signature ribbons series, which consist of clean paper strips and their calligraphy-like shadows. These contrast with his collaged billboard works, such as the Cones Series, Doors Series or Alexander's Walls. These brightly intense, curvilinear ribbon forms seem to burst forth from flat, solid-colored backgrounds. The graceful ribbonlike shapes take on a three-dimensional quality, especially as suggested by the implied shadows. This series later gave rise to alucobond–aluminum composite shadow sculptures and the series known as "Aubusson Tapestries".