I recently read of an artist who regularly re-cycles paintings that didn't work out by simply painting directly over them, no underpainting or toning of the canvas. Because I happen to have a few of those laying around I decided to try it myself and the painting above is the result. If you look very close you might still see signs of the previous painting underneath. I simply did a rough charcoal sketch of the scene and then went directly into it, what a fun experience! Oh, by the way, black and yellow make a nice green.