Heckscher pursued his interests in history and Flemish art by spending his off hours studying at the Dutch Royal Library, the Mauritshuis and the Kröller-Müller Museum, but was dismissed from the Lyceum in 1920 for "lack of scholarly potential".
[3] Having been stymied at furthering his formal art education, at the age of 19 Heckscher returned to The Hague and worked as a portrait painter.
He spent months copying panels by Jan van Eyck and Konrad Witz, took informal painting lessons with Ludwig Bartning of the Berlin Academy, and was contracted to work on an anatomical atlas.
Heckscher passed the rigorous examination[a 2] and was accepted into the University of Hamburg, but was only grudgingly given a seat in the back of Panofsky's seminar.
[6][a 3] Heckscher was released from internment early, on Christmas Day 1941, after the intervention of Canadian senator Cairine Wilson and John Lovejoy Elliott.
As director of the Duke University Museum of Art from 1970 to 1974, Heckscher coordinated the acquisition of the Brummer collection of medieval and Renaissance sculpture.
The second was presented in 1964 for his sixtieth birthday, when colleagues and students at the University of Utrecht dedicated a volume of the Nederlands Kuntshistorisch Jaarboek to him.
He received a third festschrift in 1990 for his eighty-fifth birthday, in the form of a volume titled The Verbal & the Visual: Essays in Honor of William Sebastian Heckscher.