Preliminary drawing that lies under the final painted or inked image. Prior to the eleventh century, underdrawing was often executed with a hard point, but thereafter a metal point, especially a lead point, or diluted ink was generally used. Styli, dividers, and compasses were sometimes employed in the laying out of a design throughout the Middle Ages. See also backdrawing.
Michelle Brown, Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).