Take a simple sheet of paper and crumple it at random; then, in this condition, paint it blindly (without any visual control) using an airbrush or a paint spray. In order to achieve an optimal result, keep in mind, as a unique rule, that the warm colors should be sprayed to one side, and the cool colors to the other. Then flatten the paper (you could iron it out). On every occasion, you will make a surprising discovery. In fact, it is the memory of the folds, the illusion of the initial relief that you will get painted, as each time you will register the play of shadows and light on the initially crumpled surface.