## 3 Results
The peaks of Ag (_m/z_ 106.9 and 108.9) were observed when the analyzed area was reduced and localized over the gold lamina (Figure 4a). Despite the weak signal of silver, the overlay of the Au and Ag maps indicates that the silver is localized mostly within the zone of the gold lamina (Figure 4b). It is not possible to quantify the concentration of silver in the gold leaf. However, an upper limit of ca. 1 at% to the silver concentration is a reasonable estimation since the signal of silver was not detectable by EDX [16]. Figure 4: (**a**) Time of flight secondary ion mass spectrometry (ToF-SIMS) mass spectra of the m/z regions of silver and gold for sample A. (**b**) Maps showing total ions, Au\({}^{+}\) (red), Ag\({}^{+}\) (green) distributions. The dashed white lines mark the zone of the gold leaf. On the left of this zone there is the embedding resin and on the right the preparation layer. The overlay of the Ag and Au ion distributions is shown in the last image. The total count rates are 80 for Au and 10 for Ag. Figure 3: Diffractogram of the preparation layer of sample A. The peaks of minium (Pb\({}_{3}\)O\({}_{4}\)) and white lead (2 PbCO\({}_{3}\) Pb(OH)\({}_{2}\)) are marked by empty and filled circles, respectively. Hence, ToF-SIMS measurements confirm that the gilding layer consists essentially of pure gold with traces of silver. Golden leaves were typically obtained by hammering coins which were made of pure gold [1,7] and the use of leaves of pure gold is not surprising taking into account the importance and the wealth commissioning of this wall painting. In the OM and FESEM images of sample B several layers are discernable (Figure 5a,b). The FESEM images and EDX analysis show that in sample B, the gold leaf was laid on a thicker (10-20 \(\upmu\)m) tin foil (Figure 5b). The EDX analysis reveals that the gold leaf consists of pure gold, within the detection limit of the method (Figure 5b). The layer below the metallic lamina, which contains mainly Fe and Ca, is the preparation layer. Layers, which appear dark both in the OM and FESEM images, are visible between the gold leaf and the tin lamina and the tin lamina and the preparation layer. The EDX spectra measured over these regions did not reveal the presence of other elements, besides carbon and oxygen. Thus, they probably correspond to the glue used for the adhesion of the metallic foils between them and to the preparation layer. The results of the ToF-SIMS analysis of sample B are similar to those of sample A, besides the presence of the peaks of the isotopes of tin (_m/z_ 116.9, 117.9, 118.9 and 119.9) (Figure 6a). The chemical maps of tin, silver and gold and their overlay are shown in Figure 6b. From the overlay map, it turns out that the signal of silver is localized mainly on the tin lamina. In addition, in this case silver is present in traces since it was not detected by EDX analysis. Although the analysis is limited to just one sample it should be noted that presence of silver impurities in the tin lamina could be used to derive information about the provenance of the material. The analysis of samples A and B reveals residues of the last restoration carried out between 1989 and 1992. Barium, detected by EDX and ToF-SIMS (_m/z_ 138), comes from consolidation treatments of the wall painting to transform calcium sulphate into barium sulphate. The ion fragments of fluorinated hydrocarbons (_m/z_ 50 CF\({}_{2}\)\({}^{+}\), _m/z_ 69 CF\({}_{3}\)\({}^{+}\), _m/z_ 119 C\({}_{2}\)F\({}_{5}\)\({}^{+}\) etc.) observed in the ToF-SIMS spectra probably originate from previous restorations.