Here is an example of what's called a rub out technique. After the drawing is done in black prisma on the canvas. Its fixed with workable fixative and then burnt umber is used liberally with a thinning medium like gamsol or even straight walnut oil. Its put on thickly and then rubbed out carefully to add the values to the image. This can be a very zen like experience, moving slowly and finding the rhythms in the flow of darks to lights. Only do a small portion at a time. Say a one foot by one foot section. You'll have a couple of hours of drying time to play with it. Then its a matter of adding the color.
Color is added more in glazes for the darks and more thickly in the lights. The true game with this technique is to understand the edges. Edges form and fade, ebb and flow and you control where you want to lead the eye.
