The shifts in color and/or value of the planes indicate the turning of form. The use of medium-sized planes generally requires a simplification of the forms being depicted, and the artist must make choices concerning which aspects of the form will be emphasized. The shape of each plane can be unique, or the artist can choose to use a particular shape or set of shapes for all of the planes. For instance, only triangular shapes might be used, or circular, or rectangular, etc.

Medium-sized planes used to indicate form need not be hard edged. Each plane might be created with a single brushstroke or swipe of a palette knife, and these strokes/swipes might blur into one another. Or each plane can be carefully filled in and each edge between these planes can be blurred or outlined in any number of ways (see Edges.)

The planes might be compressed near the edge of a form, elongated in the direction of the edge, in order to indicate the turning away of the form from the viewer.

Medium-sized planes can also be used in purely abstract works that create the illusion of a three-dimensional abstraction.

Featured: Jean Metzinger by Robert Delaunay.