## 3 Results
### ATR-FTIR Analysis
Indeed, it is known in the literature [14] that the area closer to the ground is where the relatively less soluble salts, such as calcium carbonate and gypsum, tend to form and precipitate as newly formed crystals, generating salt efflorescence which causes the observed detachment of the painted surface. The tensions generated by the increase in size of the salt crystals in the pores of the material can cause the detachment of the most superficial parts of the plaster and/or colored finishes, or, in the most severe cases, can even damage part of the load-bearing masonry. As was demonstrated by [PERSON] et.al. (2023), gypsum accumulation can cause hardening of the surface, which tends to decrease the superficial porosity of the material. The formation of such crusts reduces water evaporation from the surface and consequently increases sub-efflorescence formation [21]. Moving on to Panel A, the samples taken from this sampling site at different heights show different concentrations of calcium and sulphate ions (Figure 4). Figure 3: ATR-FTIR spectra of samples SG_1 and SG_2 taken from Panel E. Marker bands of carbonates (*), silicates (\({}^{\circ}\)) and sulphates (\({}^{\circ}\)) are highlighted. In fact, samples SG_6 and SG_7, taken a few cm above ground level, show higher values of these ions than sample SG_8, which was taken at a greater height close to a window splay (Figure 4). This result indicates that the wall of Panel A close to the ground level are affected by efflorescence produced by sulphation, which produces newly formed gypsum crystals that lead to the detachment of the painted surface [22]. For these samples, the presence of gypsum is confirmed by infrared analysis (Figure 5, Table 3). Typical calcite bands were observed (Figure 5, Table 3) [19,20], and can be attributed to carbonate salts, which contribute to the degradation of the wall. A similar result was obtained by analyzing samples taken from Panel C. Samples SG_4 and SG_5 were taken at lower heights, near the ground level, whereas sample SG_29 was retrieved at a greater height, near the window splay (Figures 6 and 7, Table 3). In this case, sample SG_4 shows significantly higher concentrations of both calcium and sulphate ions, with respect to samples SG_5 and SG_29. These results indicate an even stronger relationship between sampling height and ionic concentration (calcium and sulphate), once again reaffirming the previous conclusions that gypsum neoformation salts deriving from capillary rise tend to be located closer to the ground, in the vicinity of the walking surface. The pressure exerted by these salts causes the rupture of the porous material, leading to the degradation of the walls and, therefore, serious damage to the work of art, in this case the fresco. Indeed, the sampling site from which sample SG_4 was retrieved appears highly degraded, and most of the pictorial layer is no longer visible (Figure 1). In contrast, the area from which sample SG_5 was taken shows signs of superficial degradation, but the pictorial layer is still intact. Compared to the other samples taken close to the window splays (SG_8) or from the vault (SG_37A, SG_41B), sample SG_29 shows relatively high  
Figure 4: Ion concentration of samples SG_6, SG_7 and SG_8 taken from Panel A. (**a**) Ppm (\(\mu\)g g\({}^{-1}\)) concentrations of sodium, ammonium, potassium, magnesium and calcium cations; (**b**) ppm concentrations (\(\mu\)g g\({}^{-1}\)) of chloride, nitrate and sulphate anions. concentrations of calcium and sulphate. This may be attributable to external infiltrations that are specific to this sampling site. Figure 5: ATR-FTIR spectra of samples SG_6, SG_7 and SG_8 taken from Panel A. Marker bands of carbonates (*), silicates (*) and sulphates (*) are highlighted. Figure 6: Ion concentrations of samples SG_4, SG_5 and SG_29 taken from Panel C. (**a**) Ppm (\(\mu\)g g\({}^{-1}\)) concentrations of sodium, ammonium, potassium, magnesium and calcium cations; (**b**) ppm concentrations (\(\mu\)g g\({}^{-1}\)) of chloride, nitrate and sulphate anions.