Abstract: In order to polish a zone (9) of a surface (2) so as to leave visible marks, the zones of the surface which are not being worked on are covered by a mask (4) having an adhesive face and a face covered with an abrasion-resistant metal layer (7) with the total thickness (e) of the mask not exceeding 40 .mu.m so that the non-polished margin along the edge (8) of the mask (4) has a width (l) of less than about 0.1 mm, thereby making it invisible to the naked eye so that adjacent zones appear to come directly into contact without a visible separating margin.