I teach elementary art and last week we were doing a crayon resist (white crayon snowflakes to be painted over) Acouple of the children could not make their snowflakes show; I couldn't figure it out. I tried a new mark on a piece of paper, thinking shey had not leaned down enough. As I checked the brand of crayon, I saw the little word "washable" aha! the watercolor paint was washing the crayon off the paper so it barely showed. My only experience and on paper, but I would think it would wash out with warm water and soap.