## 3 Results and Discussion  
Samples A1, A4, A5, and A7 were studied by SEM-EDS. Figure 2 shows the EDS spectra acquired on areas and points as shown. Table 2 summarizes the main elements identified. Figure 2: SEM images and EDS spectra of A1, A4, A5, and A7 samples. The reported spectra correspond to areas (yellow boxes) or points (yellow spots). In the red-colored A1 and A4 samples, mercury and sulfur suggest the use of the red pigment cinnabar or vermilion and mineral or synthetic HgS, respectively. We did not attempt to discriminate between these two forms. In the dark samples, iron (sample A5) and lead (sample A7) were found. The presence of calcium in all the spectra may be due to the underlying marble substrate. Elements such as Si, Mg, Al, K, Cl, Fe, and Pb, clearly evident in the dark samples, can be attributed to the use of the mastic encrustation technique [18; 19], in which a melted mix was used as a filler of the engraved stone [14]. The infrared spectroscopy that was carried out on all samples (Figures 3 and 4) aimed to identify organic substances and salts. Figure 3 reports the IR spectra acquired on the A2, A3, A5, and A6 samples. Typical bands of calcium carbonate (1428, 875, and 712 cm\({}^{-1}\)), silicates (1020 cm\({}^{-1}\)), calcium oxalate (1624, 1322 and 780 cm\({}^{-1}\)) [20], and hydrated calcium sulfate (3537, 3407, 1620, 1110, 671, and 598 cm\({}^{-1}\)) are observed. Furthermore, the vibrational bands related to the presence of organic substances are evident: 3300-3100 cm\({}^{-1}\) (overlapping amide A, amide B, and OH stretching vibrations), 2952-2848 cm\({}^{-1}\) (stretching of CH and CH\({}_{2}\)), 1640 cm\({}^{-1}\) (amide I overlapping vibrational bands of calcium oxalate and sulfate), and 1540 cm\({}^{-1}\) (amide II) due to a proteinaceous material, presumably due to a protein binder. In the FT-IR spectra collected on the A1, A4, and A7 samples that are reported in Figure 4A, the features of calcium sulfate (indicated by dotted lines) and wax are found. Wax identification is possible through a comparison (Figure 4B) of the FT-IR spectrum of sample A1 and beeswax, spermaceti, lanolin, carnauba, and candellilla standards [21]. The wax may be unequivocally identified as beeswax. The Supplementary Materials (Figure S1) also report the comparison with the wax standards in the range of 1000-1600 cm\({}^{-1}\). Beeswax is characterized by long aliphatic chains identified in the spectra by asymmetric and symmetric CH\({}_{2}\) stretching vibrations at 2916 and 2848 cm\({}^{-1}\), respectively, and by the typical doublets attributed to the bending and rocking vibrations at 1472, 1462 cm\({}^{-1}\) and 730, 718 cm\({}^{-1}\), respectively [22]. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **Hg** & **S** & **Ca** & **Fe** & **Pb** & **Si** \\ \hline A1, A4 & X & X & X & & & X \\ \hline A5 & & X & X & X & & X \\ \hline A7 & & & X & & X & X \\ \hline \end{tabular}
\end{table} 
Table 2: Elements present in samples A1, A4, A5, and A7 detected by SEM-EDS. Figure 3: FT-IR spectra of A2, A3, A5, and A6 samples. \({}^{-}\) = gypsum; \({}^{*}\) = calcium oxalate; \(\$\) = silicate; \({}^{\circ}\) = calcium carbonate. Raman spectra were collected on the A1, A2, A6 (Figure 5A), and A7 samples (Figure 5B). In the red-colored samples (A1 and A6), the presence of cinnabar or vermilion is confirmed by the peaks at 250 and 345 cm\({}^{-1}\)[23], in agreement with the SEM-EDS results. In addition, in the A1 sample, the bands in the range of 1300-1600 cm\({}^{-1}\) indicate the presence of amorphous carbon on dark material under the red pigment. In sample A2 taken from the dark letter (E from NICODEMVS), amorphous carbon was clearly found. Figure 5B reports the Raman spectrum of sample A7 (dark letter, H from ARI/MATHIA).