The paper refers to the analytical characterization of Roman painted plasters dating back to the second century AD . The following techniques were used: optical microscopy (OM), scanning electron microscopy (SEM-EDS), micro-Raman and Fourier transform infrared spectroscopies ( µ -Raman and FT-IR), X-ray diffraction (XRPD), colorimetry and thermal analyses (TG/DTA).The investigation analysed the chemical composition and structure of the plasters, the chemical composition of the pigment layers, the use of binders and any chemical alteration of pigments as well as deterioration of the samples. Stratigraphic analysis of plasters allowed identification of their individual components, which proved helpful in finding out more about the mural painting technique employed.
The weathering of the Mt. Prinzera serpentinites (Parma province, Northern Apennines, Italy) produced dominant smectite and minor Fe-hydroxides. The mobility of the elements during weathering has been estimated using the ratio Ki = MiS/MiR, where Mi indicates the mass of a generic component i before (R) and after (S) the weathering, and using TiO2 as a practically immobile component. For prevalently to tendentially mobile elements, the degree of mobility, which in our case increases as Ki decreases, is in the order Mn ≈ Cr = Fe < V ≈ Zn ≈ Co < Ni < Si < Mg < Ca. The elements Ti, Ga, Al and Zr are prevalently immobile. The mass chemically removed by the circulating waters during weathering may reach very high values (on average 52% of the original mass of serpentinite) and the main contribution to the mass loss is due to Si and Mg. The composition of the perennial and ephemeral springs in the area is in agreement with the degree of the element mobility at least for Cr, Mg and Ca.
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