 He theorized on this idea in his 1800 treatise "Reflections and Advice to a Student on Painting, Particularly on Landscape", developing a concept of a "landscape portrait" in which the artist paints a landscape directly while looking upon it, taking care to capture its particular details.Painting outside allowed Valenciennes to capture the fleeting changes of a landscape due to light and weather.He was a proponent of artists working outside and painting the same view at multiple times of day.