# Degradation Products Assessment of the Wooden Painted Surfaces from a XVIIth Heritage Monastery
## 3 Results and Discussion
By separating the white deposit from the pigment surface (in this case blue pigment), the FTIR spectrum reveals the main specific bands of the components, Figure 9.  
The most obvious characteristic for the detection of metal soaps in oil paint layers is the intense asymmetric stretching vibration of the carboxylate head group, for Zn soaps this band is at 1547 cm\({}^{-1}\)[56]. Interestingly, the IR spectra of zinc oleate and zinc azelate also show a split carboxylate band structure, similar to the short-chain zinc soaps, Figure 10.  
Figure 8: ATR-FTIR spectra of the analyzed samples (green color pigment, blue color pigment, red color pigment). By analyzing all these results, it could be observed that in FTIR spectra of all icons' pigments, the bands of acids could be identified, in very good agreement with literature [57]. The pigments used in painting are mineral, natural, or synthetic minerals: colored clays with hydrated iron oxide (ochre) or anhydrous iron oxide (red ochre), Fe, Al, Mg, and K hydro silicate (green), silicates (blue enamel), lazurite, calcium carbonate (calcite). To obtain more shades, these pigments were blended with white, probably calcite or titanium dioxide (from previous restoration), remaining from some previous restorations' procedures, or as impurity from natural raw materials used for pigments preparation. Figure 10: The FTIR spectra of fatty acids. Figure 9: FTIR spectra of blue pigments and white deposits. The red pigment is a red inorganic pigment as Fe\({}_{2}\)O\({}_{3}\) (hematite). Hematite is identified by the FTIR spectrum that highlights the bands characteristic of hematite (\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)) located at 467 cm\({}^{-1}\) and 534 cm\({}^{-1}\). At the same time, for the purpose of obtaining different shades, the masters probably used the white Tarigrad pigment containing a natural aluminum silicate-Al\({}_{2}\)O\({}_{3}\)-2 SiO\({}_{2}\).2H\({}_{2}\)O-white, and the white lime pigment constituted by calcium hydroxide. According to FTIR spectra, gypsum from the painting can be identified (1627 cm\({}^{-1}\) and 1126 cm\({}^{-1}\)) and the proof of its application has been shown above, by visual photo taken from the church. Quartz is generally indicated by the typical doublet at 779-800 cm\({}^{-1}\)[32]. For the blue pigments, based on WDXRF, EDS, and FTIR, could be identified a mixture between ultramarine (Na, Ca)\({}_{8}\)(AlSiO\({}_{4}\))\({}_{6}\)(SO\({}_{4}\), S, Cl)\({}_{2}\), and lazurite (Na, Ca)\({}_{8}\) (AlSiO\({}_{4}\))\({}_{6}\)(S, SO\({}_{4}\)), with very small concentrations of Cr\({}_{2}\)O\({}_{3}\)-Fe\({}_{3}\)O\({}_{4}\) and ZnO. Lazurite, as an aluminosilicate, is the essential ingredient of lapis lazuli and the mineral that gives it the blue color. Lazurite is a sodium, calcium, aluminosilicate mineral that contains sulfur: the color is due to a charge transfer between sulfur atoms. ([[https://www.minerals.net/mineral/lazurite.aspx](https://www.minerals.net/mineral/lazurite.aspx)]([https://www.minerals.net/mineral/lazurite.aspx](https://www.minerals.net/mineral/lazurite.aspx)), accessed on 10 December 2022). The \"green earth\" pigment is a mixture of Fe, Mg, Al, K (mainly minerals as ecladonite and glauconite). Additionally, Cr\({}_{2}\)O\({}_{3}\)-Fe\({}_{3}\)O\({}_{4}\), viridian, hydrated chromium oxide, like green zinc or green Rinmann's green (CoZnO), and iron oxide, are present in this pigment. The presence of all these elements could be identified by elemental analysis. The green pigments based on chromium, such as viridian and chromium oxide, did not exist in the 18 th century, so it can be presumed that these pigments could be sourced from different restoration procedures which occurred in time. Figure 11 shows the FTIR spectrum of the ZnS nanoparticles. The spectra exhibit strong bands appearing in the 1114, 1259, 1384 assigned to ZnS nanoparticles [58]. The peaks at 612 cm\({}^{-1}\) are assigned to the ZnS band (i.e., corresponding to sulphides) [59; 60]. The O-H bending region due to absorbed water appears at 1620 cm\({}^{-1}\).