A wash is a technique used in watercolor painting to lay down a large area of color using a flat brush and a lot of water. It can be used to create a variety of values and colors in a painting. To create a graduated wash, which is a wash that gradually changes from one color to another, start by wetting the paper in the area where you want to lay down the wash. Then, using a flat brush, paint the edges of the area with the lightest color, and gradually work your way to the darkest color.