Gesso is normally used as a canvas primer. I use it fairly regularly in my watercolors. The effects of gesso can be seen in the watercolor paintings, "War Dance", "Force of Nature", "Summer to Winter II", "Navajo Girl in White Dress" and "Cabo". Sometimes I paint out unsatisfactory passages with the gesso and repaint the area. However, I usually use if for effect. In "Cabo", the exploding wave is gesso flipped on with a toothbrush and razor blade. In the other paintings mentioned, I poured thinned gesso into wet paint and allowed the mating to take place. It can be quite messy but the effects are sometimes breathtaking.