[5] In 1911 and 1912, Ottmann exhibited at the Artistes de la Société Moderne at the Gallery Paul Durand-Ruel together with Armand Guillaumin, Henri Lebasque and others.

[6] In 1912, Henry Ottmann exhibited at the Galerie Eugène Druet.

[7] In 1919 he was working on illustrations of La Gebre periodical in Woodcut technique together with Paul Signac,[8] Henriette Tirman and other painters.

[9] In 1920, Ottmann exhibited at the gallery Marcel Bernheim together with Manguin, Tirman, Alexandre-Paul Canu and others.

[10] In 1922, he exhibited at the Exposition du Cercle Artistique de Bruxelles together with those of Paul-Albert Besnard, Pierre Bonnard, Raoul Dufy, Othon Friesz, Charles Guérin, André Lhote, Henri Matisse, Paul Signac, Maurice de Vlaminck and others.