 He began to collect art with his wife, travelling throughout Europe for this and focussing on masters of the Dutch Golden Age.Upon the death of his father-in-law in 1931, his wife inherited a sizeable fortune, which enabled the couple to expand their collecting interests.His ongoing interest resulted in the four volumes of his famous "Répertoire des catalogues de ventes publiques intéressant l'art ou la curiosité" ("Repertory of catalogues of public sale concerned with art or objets d'art") published in 1938, 1953, 1964, and (posthumously) 1987, which gives essential details of sales catalogues published during the years 1600–1925, held in public collections in Europe and North America.