Surface investigations of bronze and brass statuary monuments in open-air exposure

Abstract The study of patinas plays an important role in the field of cultural heritage. This review reports systematic investigations of European institutional co-operations. A stable patina relies on a certain atmospheric content of sulphur dioxide from industrial immissions. Since these are decreasing recently, patina phases change to aesthetically unsightly appearances. Analytical case studies are presented of selected bronze monuments and one bronze sculpture in Europe of the period from 1807 until 1934. These were the emperor Joseph II. Memorial (Vienna, Austria), the Maria Theresia Memorial (Vienna, Austria), the Gustav II Adolf Memorial (Gothenburg, Sweden), and the Marquês de Pombal Memorial (Lisbon, Portugal), as well as one Quadriga ensemble on the Austrian Parliament (Vienna, Austria). X-ray diffractometry (XRD), atomic absorption spectral analysis (AAS), scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDX), and optical microscopy provided insights into deterioration processes in urban and marine climates. On the basis of these findings suggestions are put forward for innovative conservation interventions on bronze and brass statuary monuments in open-air exposure including laser cleaning technologies which allow the selective removal of encrustations from original patinas.