Valutazione analitica degli effetti di una pulitura laser: la statua in bronzo di Napoleone come Marte Pacificatore di Antonio Canova

The laser cleaning on bronze artefacts is becoming a very promising conservation approach and its wider diffusion would benefit from further studies of effectiveness and harmfulness. Some important references are available still the laser cleaning cannot be considered a traditional method on bronzes surfaces. In this paper, we report on the evaluation of the cleaning tests performed on an important Statue of Napoleon, depicted as Mars the Peacemaker, cast by Righetti in 1811 after a model by Antonio Canova. The sculpture is exposed in outdoor environment in the main courtyard of the Brera Gallery in Milan. The analytical survey on the corrosion products was carried out by means of XRD, ?FTIR, ?Raman; SEM observations equipped with EDS analyses were accomplished on cross sections. The results put in evidence the ubiquitous presence of brochantite Cu4(SO)4(OH)6 . Antlerite Cu3SO4(OH)4 is also present sporadically. Residues of an acrylic, wax treatment (Incralac) and of proteins were highlighted by ?FTIR. Laser cleaning tests were carried out with El.En. Combo, both in Long Q-switched (LQS) and Short free running (SFR) regimes. The evaluation of the effects of cleaning was carried out with a portable microscope and a reflectance colorimeter. Moreover a portable FTIR spectrometer was used in order to evaluate the presence of corrosion products after the cleaning. EIS (Electrochemical Impedence Spectroscopy) was used in the field on a selection of the tested areas in order to characterize the effect of laser cleaning on corrosion rate. A specially designed contact probe was used for measurements in the frequency range 100 KHz -10 mHz both before and after cleaning.