Development of an innovative film‑forming cleaning system for the removal of corrosion products from copper alloy artifacts

The cleaning procedure for copper alloy artifacts should aim at the complete removal of the defacing and harmful corrosion products of Cu(II) (copper carbonates, sulfates, chlorides) while preserving, at the same time, the protective cuprite Cu(I) layer. Traditional procedures usually involve mechanical and/or chemical methods, which both present some limits related to scarce selectivity and control of the cleaning process. An innovative polyvinyl alcohol-based film-forming system was specifically designed to overcome these problems. The main advantages of this innovative system are related to the possibility to combine a controlled chemical action, thanks to the confinement of a complexing agent into a polymeric matrix, with a gentle mechanical peeling, which is made possible by the film-forming properties of the system. The physicochemical properties of selected systemswere studied with thermal analysis (thermogravimetry, differential scanning calorimetry). After some preliminary cleaning tests on artificially aged samples, the most promising systems were used for the removal of alteration patinas from two real case studies: an ancient gilded bronze artifact and the Fontana dei Mostri Marini, by Pietro Tacca, in Florence.