Nude Studies, Raphael, red chalk and metalpoint, roughy 16 x 11 in. (40 x 28 cm); link is to zoomable images on Google Art Project, downloadable file on Wikimedia Commons. original is in the Albertina, Vienna.
Raphael is considered to be one of the greatest draftsmen in history, and this relatively well known drawing of figure studies certainly a case in point.
Note the variation in value of the hatching and the beautifully defined musculature of the back, all with sure handed and seemingly casual lines.