It is given that Darwin Musselman was a master illustrator. He was also a master of the medium at hand. During the late 1950s and early 1960s, Musselman was hired by an advertising agency which represented Bank of America, to do a series of illustrations for half-page newspaper ads, surrounding agri-business in the San Joaquin Valley.
Given reprographic capabilities at the time, the preferred method for creating crisp, high-contrast art intended for newspaper reproduction was called "scratchboard".
Scratchboard, is explained by Wikipedia
as: Modern scratchboard, as we know it originated in the 19th century in Britain and France. As printing methods developed, scratchboard became a popular medium for reproduction because it replaced wood, metal and linoleum engraving. It allowed for a fine line appearance that could be photographically reduced for reproduction without losing quality. It was most effective and expeditious for use in single-color book and newspaper printing. From the 1930's to 1950's, it was one of the preferred techniques for medical, scientific and product illustration.
Using a sharp, angled blade or scratch tool an outline is made on the surface of the scratchboard. Scratchboard can be purchased in either all black or all white sheets. [Musselman would apply india ink to a white china board.]Shadows and Highlights are created by "scratching" away at the board. Artists using the white scratchboard paint or draw [or inked] black areas onto it and then proceed to scratch into the black portions to create their drawing. Alternatively, the cleared portions of the scratchboard may be left blank for a stark black-and-white image.
As the thumbnail above for one such Bank of America ad does not give the hand or process justice, a close-up of the printed ad shows the mastery of the medium.
This close-up at left of a scratchboard sketch or comp most probably is a self-portrait, circa 1961.
This close-up of a scan from an actual board shows the detail of the highlight and shadows, and shows the underlying strength of composition found in all of Musselman's work.