Umbo (Otto Umbehr) was a pioneering German photographer in the 1920s. I did not know anything about him until I saw one of his prints at the Art Institute of Chicago today as part of an exhibition about shadows--
Unfortunately, they don't provide a larger version online, but the tones in the print are incredible. It's just slightly warm, with all the hallmarks of a silver chloride print. I think the German chloride paper available then was Agfa Lupex.
Here's a larger image of another print from the same series--
I think the era between the two world wars (especially in Europe) is by far the most interesting time in the history of photography. Painting was abondoning realism for abstraction, advanced cubism and surrealism. Photography was accepted as the true medium to present "reality". Yet many painters experimeted with cameras and soon discovered that selecive reality in front of the lens could equal experiments in painting.