Put an apple in a deep bowl. You can see that the apple takes up space inside the bowl. That perception of filled space is the primary characteristic of mass.
Visual mass consists of areas of color. Whether you paint an apple or just a block of color, the result has visual mass. Every characteristic of color – hue, value, intensity, color quality, temperature,apparent weight, and apparent distance – is a secondary characteristic of mass.
When you think of drawing, you usually think of line. In order to suggest the shapes of forms, line drawing concentrates on the outline of the boundary edges or the contours of the object you’re drawing. In contour drawing you always feel as if you’re touching the surface. An object drawn with simple contours doesn’t carry very much visual weight.
However, there’s a different kind of drawing that’s more useful to the painter – mass drawing. Mass drawing is more concerned with how shapes fill space than with the contour, or outline, of shapes. You make a mass drawing with the side of your pencil, not the tip. An object in mass drawing always feels as if it has weight.
Because it reports the lights and darks as they eye sees them, a mass drawing usually starts somewhere in the middle of the form and works its way out toward the edge, whereas a line drawing first finds the edge and then works its way in toward the center of the form.