Draw an even tone to depict a plane parallel to the picture plane. Then draw a blend
describing a plane that is not parallel to the picture plane.
Draw, in succession, a blend that describes a cylinder; a cone; and a sphere.
Using line only, draw the five basic forms as they would appear when concave and when convex. Next, put the appropriate shadow and light shapes on these drawings. include reflected light on the convex forms. Arrange the contrast so that some forms appear to advance toward the foreground and others recede into the background.
Again using only line, draw two squares with a circle inside each. Then draw the lights and darks so that one circle looks like a concave form and the other convex.
When a composition has only middle and light values overall, a haze or mist seems to cover the picture. When only middle to dark values are used, the picture seems to be in a cast shadow. When a full range of values that includes extremes of dark and light is used, the picture seems to be in clear air and strong light.