## 3 Results
The FTIR analysis of each paint mock-up (F and SB) showed the characteristic bands previously identified in each pigment, shown in Table 2, except for VER-G-F. In addition, bands assigned to calcium carbonate (i.e., the lime-based mortar, marked in Figure 4a) were observed in both paints (F and SB) regardless of the pigment used: at 1795 cm\({}^{-1}\) (C=O) and 875 cm\({}^{-1}\) (CO\({}_{3}\)\({}^{2}\)- antisymmetrical bending) [36; 45]. These bands were generally more intense on F paints. An additional band around 1400 cm\({}^{-1}\) (CO\({}_{3}\)\({}^{2}\)- stretching), also associated with calcite [36; 45], was exclusively present in the F paint spectra. In relation to NE as the binder, Figure 4a shows the FTIR spectra for the colloidal solution NE (after polymerisation) and is compared to EG-SB (silicate), CHR-G-SB (oxide), and VER-R-SB (sulphide) paint mock-ups. Bands around 1065, 1045, and 445 cm\({}^{-1}\) (Si-O) were present in the spectra of all the SB mock-ups, assigned to the formation of silica gel [63; 64]. In silicate pigments, e.g., EG-B-SB; however, the bands were covered by the characteristic Si-O bands of the pigments, marked with a black rectangle in Figure 4a (in this case assigned to cuprorivaite, see Table 2). In VER-R-SB (sulphide), the silica gel band could also be ascribable to SiO\({}_{2}\) present as an impurity. Regarding the silanol bands from NE, the broad band at 3700-2800 cm\({}^{-1}\) (Si-OH stretching) decreased in intensity, and the bands at 1645 cm\({}^{-1}\) (Si-OH bending) and 960 cm\({}^{-1}\) (Si-OH stretching) disappeared, overall suggesting the good polymerisation of NE [63; 65; 66]. Lastly, regarding the alteration observed in VER-G-F (Figure 2i), Figure 4b shows the FTIR spectra for the raw pigment compared to that of the fresco. The characteristic bands assigned to the acetate changed considerably in the F paint. The three large characteristic bands related to the water molecules associated with the acetate ion (Table 2), were no longer visible in the F paint. A broad band between 3600 and 2700 cm\({}^{-1}\) appeared in its place, also assigned to -OH stretching [55] (marked with a black rectangle in Figure 4b). Regarding copper carboxylate groups (COO\({}^{-}\)), the band present in the powder pigment at 1600 cm\({}^{-1}\), shifted to 1536 cm\({}^{-1}\) in the F paint (marked with a black arrow in Figure 4b). Lastly, the bands assigned to O-C-O bonds shifted to lower wavenumbers (670 and 620 cm\({}^{-1}\), respectively) and lost intensity in the F paint (marked with a black rectangle in Figure 4b). The morphological and textural study of the surface by SEM revealed that in some cases the NE binder did not fully penetrate the _intonaco_, remaining in part on the surface. A cracked xerogel appeared on the surface of the SB mock-ups (marked with white arrows in Figure 5a). The presence of pigment particles on the surface was also observed to a greater or lesser extent in all the SB mock-ups (Figure 5b), regardless of the pigment composition. The study of cross-sections of the SB mock-up by SEM revealed fissures which in places penetrated up to the _intonaco_, and even within the SB layer itself (Figure 5c). The study of the SB paint mock-up cross-sections by PLM and SEM allowed us to evaluate the distribution of pigment particles within the paint layer and the degree of adhesion of the paint to the _intonaco_. Silicate-based SB paints presented a homogeneous distribution of the pigment particles, especially synthetic EG-B-SB (Figure 6a) and UL-B-SB (Figure 6c). The others (natural LA-B-SB and GE-G-SB, Figure 6b,d, respectively) were more heterogeneous, with pigment particles protruding from the paint layer, especially in GE-G-SB. All the paints showed small fissures to a greater or lesser extent, though they were much more evident and pronounced in GE-G-SB (marked with a white arrow in Figure 6d), in addition to a slight detachment of the paint layer from the _intonaco_.