I have learned from experience that it is useful to begin by drawing one's picture clearly on a virgin canvas, first having noted the desired effect on a white or gray paper, and then to do the picture section by section, as immediately finished as one can, so that when it has all been covered there is very little to retouch. I have noticed that whatever is finished at one sitting is fresher, better drawn, and profits more from many lucky accidents, while when one retouches this initial harmonious glow is lost. I think that this method is particularly good for foliage, which needs a good deal of freedom.