Robertson's printmaking discussed on pages 148 - 149 in A Spectrum of Innovation - Color in American Printmaking 1890-1960.' by David Acton, 1990, Worcester Art Museum.
Acton writes: "Robertson looked to Native American art for decorative motifs that bore no recognizable meaning. He derived the arcs, floating circles, serpentine slashes and meandering lines of his designs of the 1940's from the decoration of pottery made by the ancient Caddoan Indians of southwestern Arkansas."