L'INTERVENTO DI PULITURA LASER SU TRE CALCHI IN GESSO DELLA COLLEZIONE DELL'ACCADEMIA DI BRERA

The present paper regards about the laser cleaning intervention on three plaster casts, the Flora Farnese, the Pallade di Velletri and the Fauno Barberini, in the framework of the pilot restoration for the conservation of the Plaster Casts Collection of the Brera Academy of Fine Arts. The three artefacts were objects of a severe decay that altered the plaster casts integrity and impeded a correct lecture of the surface. Before using the laser tecnology, preliminary wet and agar gel cleaning were carried out. This metodology didn't allow a complete deposits removal; in fact unwanted particles were partially penetrated in the gypsum matrix porosity and the traditional methods did not allow to eliminate the grey layer visible on the artefacts. Hence a Nd:YAG system operating in QS mode, was used as an alternative metodology. Several laser cleaning tests were carried out on plaster casts surface and instrumental analysis were carried out to evaluate the laser effects. Laser cleaning was completed at 532 nm wavelength. The possibility to calibrate continuously the operating parameters permitted to ensure selectivity, gradual cleaning and safety conditions needed to reach the desired cleaning level. The laser system allowed the treatment of a sensible, porous material like gypsum is, respecting at the best the surface morphology.