When the contents of Rubens’ studio and his collection were gathered for an estate sale, one of the last items listed was ‘Une quantité de visages au vif, sur toile, & fonds de bois, tant de Mons. Rubens, que de Mons. van Dyck’. These head studies testify to the practice undertaken by Rubens and his studio of making ad vivum oil sketches from models, which served as working tools for assistants. Many such studies, spontaneously and rapidly finished, were painted on composite panel supports and then sometimes enlarged and further worked up. This hitherto unrecorded sketch is an excellent example of this workshop practice and the manner of execution indicates a close affinity to Rubens. An attribution to the young van Dyck, then working in Rubens' studio, has been proposed.