When this painting was first reproduced, in the May 1914 edition of the journal Les Soirées de Paris, it was titled La Glace sans tain, or "the mirror without silvering," referring to a device known as a Claude mirror: the dark, red-framed square in the picture. Many artists used one of these slightly convex, dark-tinted mirrors to clarify their compositions; a scene reflected in it is less colorful than life, its compositional elements accentuated. Something close to that effect is visible here in the structured vertical and horizontal bands and the cool blue palette that Matisse painted over other layers of color, some of which are still visible. As he simplified forms he reinforced them with incising and scraping, in, for example, the cloud at top left.
Gallery label from Matisse: Radical Invention, 1913-1917, July 18–October 11, 2010.