## 3 Results
### SEM-EDS and \(\mu\)-Raman  
The paint layers of the three samples from Panel A (SG16, SG17, and SG47) share the same main pigment, that is, ochre, either red (hematite) and/or yellow (goethite), applied on the plaster \"a fresco\". This is suggested by the absence of microstructural discontinuities between the plaster and the paint traces. Generally, the ochres are mixed with fine particles of C black. The stratigraphy of sample SG16 is worthy of further remarks since it is the only one showing \"a secco\" layers, with additional pigments applied on the dry plaster (Figure 4): one green-blue middle layer made of malachite and one yellow-brown surface  
Figure 3: Microphotographs of thin sections of the samples SG16, SG17, SG23a, SG25, SG39b, SG40, SG46, and SG47. The capital letters “**A**”, “**B**”, “**C**”, “**D**”, “**E**”, and “**F**” indicate the different layers visible in cross-section, with “**A**” being the innermost (the plaster) and the others (mostly pigmented) ordered by decreasing depth. Sample SG40 shows a break between the layers consisting of highly purified plaster (**E**) in which remnants of a blue pigment can be seen (indicated by the red arrow), probably due to the use of a dirty brush or the mixing of pigments from the underlying layer (**D**). layer probably composed of Cr yellow (because of the detection of Pb chromate grains); this last identification, however, needs to be taken with reservation. Finally, the SEM-EDS analyses of sample SG47 also highlighted the presence of gypsum particles and several surface irregularities and detachments. Figure 4: Sample SG16: SEM-BSE image with associated SEM-EDS spectra from the spots indicated, and \(\mu-\)Raman spectra calculated on two different paint layers (actual analyses in red, reference spectra from mineral databases in blue and pink). The SEM-EDS analysis revealed similar microstructural and compositional characteristics for samples SG9A and SG9B. The samples are layered, with an air lime-based arenaceous plaster (A) on which two paint layers (B, ca. 20 \(\upmu\)m; C, ca. 8 \(\upmu\)m) are visible (Figure 5). A detachment is observed between layers B and C. Layer B is more compact than C and both are air lime-based. The EDS microanalysis of the small areas of the painted layers reports the presence of iron oxyhydroxides in layer B, and calcium phosphate (bone black), zinc oxide, and iron oxyhydroxides as pigments in layer C. The compositional traverse in Figure 5 shows the gradual diffusion of phosphorus in the underlying layer, confirming the hypothesis of an \"a fresco\" painting. The correlation between K, Al, Si, and Fe in layer C might indicate the presence of red bolus [34]. S is due to the presence of gypsum. Additionally, in SG10, two lime-based layers are visible. Layer B is ca. 20 \(\upmu\)m thick and pigmented with hematite. On layer B, an additional pigmented layer (C) partially detached from the previous was recognized, with a thickness of less than 10 \(\upmu\)m (Figure 6). The two samples of Panel B (SG11 and SG12) show two painted layers applied on an air lime-based arenaceous plaster (A). In SG11, layer B can be distinguished by its content of calcium phosphate, zinc oxide, red ochre, and gypsum. Replicated measurements on two other detail areas on layers B and C of the same fragment provided similar data. The binder in layer C is probably of organic origin. Sample SG12 is layered, with an air lime-based arenaceous plaster (A) on which a B layer is visible in adhesion and a laterally discontinuous C layer. The presence of Mn in the Fe-rich particles in layer B may indicate the use of Sienna, whereas layer C is a lime paint with red ochre. Some gypsum was also identified in this last layer. In Panel C, SG13 is stratified, with an arenaceous lime plaster (A) on which there are two painted layers. Layer B has a gradual stratigraphic contact with A and sharp contact with C. The EDS chemical mapping shows a high P content in layer C due to some calcium phosphate.