Face of Christ on St. Veronica’s Cloth (alternately: Sudarium of Saint Veronica), Claude Mellan, engraving on paper, roughly 17 x 13 in. (43 x 31 cm); in the collection of the Metropolitan Museum of Art, (click on image to zoom, click small down arrow to download)
This remarkable engraving by 17th century French engraver and painter Claude Mellan consists of a single spiral line!
Beginning on the tip of the nose, the line spirals outward, its passages of increasing or decreasing thickness defining the darks and lights of the image.
To understand how even more remarkable this accomplishment is, see the Met’s page on engraving, and how it’s done.