## 3 Results
### SEM-EDS and \(\mu\)-Raman
Ochre is present in both layer B and layer C.  
The painted surface of sample SG46 is also composed of ochre; in this case, however, the yellow ochre (goethite) and red ochre (hematite) are not mixed, with the former composing the \"a fresco\" bottom layer, and the latter, the upper \"a secco\" layer, also including scattered C black particles. The upper layer also recorded SEM signals of S and Cl. From a microstructural point of view, the sample shows a distinct surface microcracking, with fractures expanding across the paint layers or partially separating them from the plaster substrate. The sample from Panel D (SG25) again has red ochre (hematite with some parts of magnetite) as the pigment originally used for the \"a fresco\" layer. The upper layer, probably applied \"a secco\", is blue and made of a combination of ultramarine and Ti white, suggested by the detection of the phases lazurite and rutile; some broad Raman peaks (from about 1300 to 1500 cm\({}^{-1}\)) also point out the presence of organic matter. The SEM microanalyses also revealed the presence of baryte. Finally, another layer, differently oriented in respect to the others (that is, not observed on the surface but sinking into the plaster), is formed of S and Ca (gypsum?) and covers an inner thin red film; although this has the same color as the red ochre layer and is also in direct contact with the substrate, its composition is slightly different, with frequent SEM-EDS signals of Fe, Pb, and Ba from baryte. SG14 and SG15 were sampled from Panel E. In the first case, layer B is present discontinuously on layer A. The stratigraphic contact is sharp, with complex geometry. The binder of the plaster (A) is air lime. Chemical mapping reveals the presence of Ca phosphate, Zn oxide, and ochre (Figure 7). In the second case, layer B identified by optical microscopy shows no clear separation from layer A. There, Fe enrichment and carbonaceous inclusions are detected. The outer surface of B also shows the presence of gypsum. Layer C is poorly preserved and consists of gypsum and calcite. Figure 5: SG9A, SEM-BSE image (**bottom**) of the outer portion of the sample (plaster layer “**A**” and paint layers “**B**” and “**C**”) and the EDS traverse across the identified layers (**top**). The intensities of the K and L lines of the elements in the legend are normalized to better detect lateral variation in the painted layers. Figure 6: SG10, SEM-BSE image of the outer portion of the sample (plaster layer “**A**” and paint layers “**B**” and “**C**”). Light grey tabular fragments of hematite (Hem) occur as pigment in layer **B**. Figure 7: SG14, SEM-BSE image of the outer portion of the sample and related EDS maps of Zn, Fe, and P.  
The sample from Panel \"sky\" (SG23A) is a non-painted plaster fragment. The samples from the vault (SG39B and SG40) are the most complex compositionally, considering their stratigraphy composed of six layers. Sample SG39B has four different paint layers above the plaster substrate: the first and deepest, applied \"a fresco\", is made of red ochre (hematite with magnetite); the second, applied \"a secco\", is blue and made of azurite (with traces of Zn and As)--it is detectable only in a very small area and never on the exposed surface; the third, more continuous but almost colorless, has an ambiguous composition, enriched in gypsum (from the SEM signals of S and Ca) and resins or organic polymers (from the \(\upmu\)-Raman spectra); finally, the fourth, the most superficial, covers the entire surface and is blue and composed of ultramarine (lazurite), with traces of Pb particles (pointing out the possible mix of ultramarine with Pb white) and Ba (probably bartyte) (Figure 8). With regard to sample SG40, this is formed by two main stratigraphic domains.