Never, never do I set to work on a canvas in the state it comes in from the shop. I provoke accidents - a form, a splotch of color. Any accident is good enough. I let the matiere decide. Then I prepare a ground by, for example, wiping my brushes on the canvas. Letting fall some drops of turpentine on it would do just as well. If I want to make a drawing I crumple the sheet of paper or I wet it; the flowing water traces a line and this line may suggest what is to come next.