Joseph Conrad (2015). “The Complete Novels of Joseph Conrad - All 20 Works in One Premium Edition: Including Unforgettable Titles like Heart of Darkness, Lord Jim, The Secret Agent, Nostromo, Under Western Eyes and Many More (With Author’s Letters, Memoirs and Critical Essays)”, p.4543, e-artnow
Interview in "Artforum" Magazine, November 1969; as quoted in "Six Years: The Dematerialization of the Art Object from 1966 to 1972" by Lucy R. Lippard, University of California Press, (p. 121), 1973.