The monumental five-volume catalogue of the collection Mahillon commissioned, between 1880 and 1922, also included four versions of his essay on the methodical classification of both ancient and modern instruments, which was to serve as the basis for the organological Hornbostel-Sachs classification systems, still used today. Beginning in 1877, Mahillon also created a restoration workshop in the MIM, where he employed and trained a worker, Franz de Vestibule, to restore damaged articles and make copies of unique instruments in other public collections.