IL RESTAURO DELLA FACCIATA DIPINTA DA GIOVANNI STALF SU DISEGNO DI FRANCESCO SALVIATI NEL PALAZZO MELLINI FOSSI A FIRENZE

Some notes on the techniques used, and an art-historical essay, were published in the last number of this journal; here we give an account of the complex work of restoration that lasted almost three years. At the beginning of the restoration (1994) the painting's state of preservation was disastrous, with a general tendency for the colour to come away from the plaster, some detachment of the plaster from the mural support, an abundant and generalised presence of gesso (calcium sulphate) caused by atmospheric acidity and suggesting that the calcium carbonate used as a binder, as well as the plaster at the painting interface, had turned into calcium sulphate, causing loss of adhesion to the support. The thick grey-black encrustation which covered the façade consisted of gesso with particles of carbon and silicates (hydrocarbons and ordinary dust), typical of stone monuments exposed to the elements. Rainwater from the guttering had resulted in carbonisation. Before commencing the restoration, as is the usual practice in our laboratories we began a series of scientific investigations involving stratigraphic analysis, chemical microanalysis and spectrophotometric analysis. From these investigations it appeared that the painting still present on the greater part of the façade had been executed by the technique "a calce", and that the thick encrustation consisted of a mixture, in varying proportions according to its distance from the pictorial surface, of gesso, calcium oxalate, nitrates, carbon and silicate particles. The restoration envisaged the following phases: consolidation of detached colour, cleaning, anti-sulphate treatment, final consolidation, pictorial restoration. Work ended in autumn 1996, and it is regarded as one of the most important restorations of recent years in Florence.