He began to paint CoBrA style pictures in the early 40's, at least 5 years before the formation of the CoBrA group in 1948.After the World War II Gilbert returned to live in Paris, where he exhibited with the Salon des Réalités Nouvelles and Salon des Surindépendants. In 1953 Gilbert organized a series of 12 lithographs, which included prints by himself, Constant and Hilton. Both Constant and Gilbert began to work in three dimensions constructing . metal reliefs, objects, sculpture and even houses.