Italian translation of an article from the burlington magazine (1962 pp 56-59). A contribution to a discussion on the cleaning of pictures in the national gallery, london. Stresses the views of the old masters themselves with respect to the appearance of their paintings. Cleaning may be difficult because of the wide variety of varnishing materials used. Varnish may have been used as a painting medium. Artists may have painted their pictures in a higher key to compensate for the dark colour of early varnishes, thus cleaning would change the intended effect. Tinted varnishes may have been used for aesthetic effect. Artists may have anticipated the patina effect and painted in lighter and brighter colours to compensate for it. 41 footnotes, bibliographic references.