## 3 Results and Discussion
### Paint Layers  
Microscopic imaging of the painting is particularly able to represent the peculiar technique of paintings consisting of precise brushstrokes using either a hatching or dotting method. Figure 6 shows the composition of the detail of the right eye of [PERSON], where the separate individual dots of colors are well-represented with different magnification: blue dots made of lapis lazuli for the iris, red ochre for the skin, and vermilon for the lacarimal caruncle. The IRFC images offer a first representation of the differently used pictorial materials, successively confirmed and detailed through spectroscopic and hyperspectral imaging. The blue of the iris is rendered with a red false color, which corresponds to the precious pigment lapislazuli, while the vermilon appears yellow in false color. Figure 7a shows the map of the analyzed points by means of FORS and XRF on the [PERSON] portraits, and Figure 7c shows the pigment distribution map obtained by applying the SAM algorithm to the hyperspectral image in Vis/NIR and for comparison with the results of the FORS analysis. For each point and region, the table reports the  
Figure 5: Pipeline of the elaboration for the underdrawing extraction: (**a**) SWIR image, (**b**) local contrast enhancement, (**c**) binary mask with ad-hoc parameters, (**d**) binary images filtered on the basis of spatial features (dimension and circularity of pixels), where the underdrawing is highlighted. Figure 6: Detail of the right eye of [PERSON]: microscopic images at different magnifications (50\(\times\) and 220\(\times\)). identification of pigments and pigment mixtures made by cross-referencing data from the different surveys [25; 26]. The qualitative, but immediate, representation through the pseudo-colors mapping made by hyperspectral imaging was analytically improved with the combination of point spectroscopies, extending the local materials characterization to the entire painting surface. With the aim of studying the artist's painting technique, including other artworks, it is interesting to compare the materials in the portrait of [PERSON] with those found in the portrait of [PERSON]. Thanks to the SAM mapping represented in Figure 7c, it is possible to confirm a similar execution technique and the comparable pigments used in the realization of the two paintings: calcium-based white pigment for the realization of the ruffs, ochre and vermilion for the reds and skin, and the use of lapis lazuli and gold for the armor. Only the mapping of the skin tones in the portrait of [PERSON] shows a greater use of vermilion, used in some regions of the face to define a greater chromatic richness of tones and shadows. Dark areas in the background resulted in being made with carbon-based or other organic materials, since no significant element was found in XRF, and the low reflectance caused no detectable FORS information. The skin tones of [PERSON] indicate the presence of vermilion and ochre, in different concentrations, mixed with lead white in the highlights. The brown tones of the beard and hair are made with burnt earth, while the blue eyes are painted with small dots of brush with lapis lazuli. The pigments used for the armor and for the golden decorations reveal the use of precious materials, such as lapis lazuli, silver, and gold, the latter in the form of shell gold, resulting from microscope image (Figure S4). Considering the pendant of the Santisima Annunziata, the symbol of the highest honor of the House of Savoy, despite the small size, a rich palette emerges on  
Figure 7: Portrait of [PERSON]: (**a**) map of analyzed point using FORS and XRF spectroscopy, (**b**) result of the SAM algorithm to map similar pigments and pigments mixtures represented in pseudo-colors, (**c**) SAM mapping of [PERSON] for materials comparison.