Drawing by Adolph Menzel. I love unmade beds as a subject. In this one, Menzel really has the values right, and you can feel the heaviness of the duvet and sheets. You get a sense of how some things are resting on other things, and also how some are in front and come forward, and some are behind and recede.

According to Wikipedia, Menzel was the second most prominent 19th century German artist, after Caspar David Friederich, but I think his reputation must have faded after his death.