## 3 Results and Discussion  
### Panel A \"Il Bacio di Giuda e la Cattura di Cristo\"  
In the case of the SG_18B sample, the spectrum obtained from the yellow-orange area (Figure 2) presents two structures, at \(\sim\)1180 and \(\sim\)1270 cm\({}^{-1}\), that could be attributed to the goethite of yellow ochre; the contribution of this mineral expected at \(\sim\)440 cm\({}^{-1}\) is probably masked by the high value of fluorescence, mainly due to the binding media. Additionally, the contribution of calcite, reasonably coming from the preparation layer, is visible. The sample SG_19, collected from a green leaf (Figure 1), shows a four-layer stratigraphy (Figure 3): starting from the surface, we can observe a greenish layer (A) with a thickness of about 25 \(\upmu\)m, a blue layer (B), with the same thickness, related to the sky, a red layer (C), and the substrate consisting of the mortar (D). The elemental analysis (SEM-EDS; Table 2) shows the presence of abundant copper in the green and blue grains of the A and B layers, which is due to the use of malachite and azurite pigments. The presence of large amounts of calcium in layers A and B could indicate the use of a white pigment (_Bianco di San Giovanni_?) to lighten the green and blue tones; layer C is made of red ochre film (_morellone_) to protect the pigments from the alkaline effects of the mortar. The XRD analysis of the selected green grains from this sample shows the presence of malachite, along with traces of quartz (Table 3). The sequence of layers of the sample SG_20 (obtained from the base coat of the sky, see Figure 1) consists of only three layers (Figure 4): a very thin (less than 20 \(\upmu\)m) blue film (A), a red layer (probably _morellone_) (B), and the mortar substrate (C). The SEM-EDS (Table 2) investigation displays the use of azurite for the outer layer, taking into account the copper content, and red ochre (_morellone_) for the second one. As well as in the sample SG_19, a similar consideration about the presence of a high percentage of calcium in the blue layer is necessary. Figure 3: (**a**) Micrographs of SG_19 cross section obtained using OM, showing the four-layer stratigraphy; (**b**) SEM-EDS back-scattering electron image of the four layers. Figure 2: Raman spectrum collected on yellow-orange area of SG_18B sample. As for the fragment SG_21A, taken from a blue wash above the window (Figure 1), the observation under the light microscope shows two different shades of blue on the surface (layers A and B), overlying a red layer (C), and the substrate of mortar (D) (Figure 5). The blue layers differ in tonality. The first one (A) is lighter and contains black grains of small size, while the second (B) displays a more intense blue tone and a coarser grain size. In addition, the B layer is not continuous along the section, suggesting a loss of colour from the original film in some areas, and supporting the presence of a secondary integration with the lighter blue pigment belonging to layer A. The SEM-EDS analysis (Table 2) of layer A detected the presence of iron and zinc, suggesting the use of a mixture of Prussian blue and Zinc white. These materials clearly attest to the non-original nature of layer A, allowing us to date the intervention to not before the second half of the XVIII century. The punctual investigation of the black grains observed inside layer A revealed the presence of calcium and phosphorus, due to the use of a bone black pigment, probably added to make the tone of blue darker (too much light), making it uniform with coat B. The elemental analysis confirms the use of azurite for the coarse blue grains of layer B and red ochre for the _morellone_ C layer. The SG_22 greenish fragment was collected from the sky background (Figure 1) that was probably subjected to chromatic alteration. The cross section, observed under the optical microscope, features three layers, including an altered green layer on the surface (A), a thin red layer, probably _morellone_ (B), and a substrate consisting of mortar (C) (Figure 6).