In 1925, he became Lincoln Professor of Classical Archaeology and Art at the University of Oxford, a position he held until 1956. He specialised in Greek decorated pottery (particularly black-figure and red-figure), and became a world authority on the subject. He adapted the art-historical method initiated by Giovanni Morelli to attribute the specific "hands" (style) of specific workshops and artists, even where no signed piece offered a name, e.g. the Berlin Painter, whose production he first distinguished. He looked at the sweep of classical pottery—major and minor pieces—to construct a history of workshops and artists in ancient Athens. The first English edition of his book, "Attic Red-figure Vase-painters", appeared in 1942 (in German as "Attische Vasenmaler des rotfigurigen Stils", 1925).