Imi Knoebel Heptagon 1988 Acrylic on wood Signed and dated on the reverse with brush in red, yellow and blue: Imi 75–88. There too a stamp in red: 66 (or 99) 19 1/8 × 20 7/8 × 2 3/4 in. Berliner Sparkasse Collection (acquired1994 at Galerie Silvia Menzel, Berlin)