Taking raw umber and white (oil paint), mix up a tone that you think
equal to the half tones of the cast before you. Extreme care should be
taken in matching this tone. Now scumble this with a big brush equally
over the whole canvas (or whatever you are making your study on). Don't
use much medium, but if it is too stiff to go on thinly enough, put a
little oil with it, but no turpentine. By scumbling is meant rubbing the
colour into the canvas, working the brush from side to side rapidly, and
laying just the #thinnest solid tone# that will cover the surface. If
this is properly done, and your drawing was well fixed, you will just be
able to see it through the paint. Now mix up a tone equal to the highest
lights on the cast, and map out simply the shapes of the light masses on
your study, leaving the scumbled tone for the half tones. Note
carefully where the light masses come sharply against the half tones and
where they merge softly into them.