Focus on soluble salts transport phenomena: the study cases of Leonardo mural paintings at Sala delle Asse (Milan)

The program of investigations on “Sala delle Asse”, which hosts a monochrome landscape attributed to Leonardo, in the Sforza Castle in Milan recently concluded the first step. Results of the analytical tests for the characterization of materials and their damages showed the high diffusion and concentration of nitrates and sulphates on the surface of the monochrome at the edge with the restoration mortars, on the right side of the north-western wall. On the base of the scientific literature and laboratory tests, the researchers identified a threshold of RH above which deliquescence of salts could easily occur. Microclimatic monitoring results informed that during the most humid days in spring, summer and fall, RH trespasses this threshold, with a frequency of about 30 events/year. After an accurate analysis of air temperature (T °C) and relative humidity (RH) resulted that the exterior changes especially affect the interior climate at some summer conditions as middle-high speed of wind and, especially, its direction due to some cracks and holes in the north western exterior wall of the hall.