I am teaching myself to paint with watercolors. I went to my local book store and bought a book that comes with a DVD written by Birgit O'Connor. Above is an excercise that has helped me understand how watercolor moves. The book exposes essential watercolor laws to non-painters like myself but are obvious to others. Here are a couple of laws:
(1) [Watercolor] can't move without water.
(2) Backwashes happen when the moisture level is uneven.
(3) Watercolor can be lifted to varying degrees.