In 1963, Koehler had reached another creative height with the production of his unique glass collages known as 'Contre-Collages'. Layers of paper sourced from newspapers, advertisements, magazines and printing materials were glued onto a piece of glass, which Koehler then smashed with a hammer. Subsequently, he covered the broken glass with black or coloured ink which could seep into the cracks, leaving on the paper underneath a linear image created by pure chance.

These works are a testimony to Koehler's powerful creative mind and individual expression which can be situated central to the German 1950s avant-garde, matching the endeavours of Otto Piene, Heinz Mack, Emil Schumacher and Wolf Vostell.

Koehler's works are present in countless museums including: Kunsthalle, Bielefeld; Museum Ostwall, Dortmund; Museumlandschaft Hessen, Kassel; Landesmuseum, Münster; Museum Wiesbaden, Wiesbaden; Märkisches Museum, Witten; Städtische Galerie, Wolfsburg; Museum Moderner Kunst Stiftung Ludwig, Vienna.