APPROCCIO MULTI-ANALITICO PER LA CARATTERIZZAZIONE DI PATINATURE ARTISTICHE SU OPERE IN BRONZO DI EPOCA CONTEMPORANEA

Artificial patination of bronze is an ancient technique aimed at improving the superficial aspect of the artistic manufacts but also conferring protection against environmental agents. It is mostly based on empirical recipes and little is known of the final corrosion compounds formed on the patinated object. In addition, prior to applying the artificial patina, chemical treatments (pickling) and/or mechanical working (polishing, sandblasting, hammering) are usually carried out with finishing purposes. These treatments may influence the final result in terms of patina's composition and morphology, adhesion to the metal, aesthetic features and durability. A better understanding of artificial patinas will not only allow developing appropriate methods of conservation and restoration, but also differentiating between artificial and natural patinas. To reach these goals, a number of bronze specimens was prepared in foundry following the same procedure and recipes adopted for artistic production, with different combinations of chemical-mechanical working and three patinas (green, brown and black) chosen among those preferred by contemporary artists. A multi-analytical characterization of the specimens was carried out through reflectance and ATR-FTIR spectroscopy, XRD, colorimetry, optical microscopy, SEM-EDS, which clearly evidenced differences in artistic patinas' composition, structure, thickness, porosity, adherence and uniformity.