After the First World War, as donors and philanthropists as well as Belgium's famed instrument makers started becoming scarcer, only about a thousand instruments were added to the collections between 1924 and 1968. Until 1957, the curators at the head of the MIM; Ernest Closson (1924–1936), his son Herman (1936–1945), and René Lyr (1945–1957) limited themselves to preserving the already collected instruments, in not always satisfactory conditions. Ernest is notable for editing several articles on Belgian makers for the National Biography and devoting a long monograph to "La facture des instruments de musique en Belgique", which appeared at the 1935 International Exposition held in Brussels.