General indications are first given about the purpose and the use of surface modification techniques in art. The activity in this field at the "Centre de Recherche et de Restauration des Musées de France" is then described: surface assessment, techniques of restoration, recommendations for conservation. The authorized range of scientific investigation on patrimonial objects is discussed. A methodological analysis of various surface characterization methods and surface treatments is proposed. A limited number of demonstrative examples show the application of these methods in different areas at the Louvre.