# Degradation Products Assessment of the Wooden Painted Surfaces from a XVIIth Heritage Monastery
## 3 Results and Discussion
The stretch vibration adsorption of ZnO at 420\(-\)460 cm\({}^{-1}\) is not detected, which indicates that ZnS was not oxidized to ZnO during the preparation as reported by [PERSON] et al. [61]. Metallic soaps contain pigments based on heavy metals, such as lead or zinc, which react with the fatty acids resulting from the hydrolysis of glycerides in the oil binding medium or from the protective layers [62]. Soap inclusions in oil paintings, studied by gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR), concluded that they contain saturated C16 (palmitic) and C18 (stearic) zinc carboxylates, and relatively small amounts of zinc azelate (C9) [63; 64]. In Raman spectra, Figure 12, a strong band near 545 cm\({}^{-1}\), along with a weaker band near 1098 cm\({}^{-1}\), are the features of Ultramarine pigment (artificial Lapis lazuli) [65; 66; 67]. By EDS and WDXRF, were identified the four key elements (apart from oxygen) of this pigment, Na, Al, Si, and S.  
The band near 1085 cm\({}^{-1}\) is arising from calcite, and the presence of BaSO\({}_{4}\) is evidenced by the band near 987 cm\({}^{-1}\). The presence of Ba, S, and Zn above identified indicate that the main component is lithopone (BaSO\({}_{4}\) + ZnS). Additionally, the presence of Ca indicates the presence of CaCO\({}_{3}\) (calcite) near 1085 cm\({}^{-1}\) was observed in the spectra from the same area obtained. Figure 11: The FTIR spectra for zinc carboxylates. Figure 12: The Raman spectrum of fatty acids. The three bands near 224 cm\({}^{-1}\), 291 cm\({}^{-1}\), and 408 cm\({}^{-1}\), and the weaker band from 611 cm\({}^{-1}\), are indicative of the presence of red ochre (Fe\({}_{2}\)O\({}_{3}\) + clay). Of the known red pigments, only haematite (the basic component of red ochre) contains iron. The two peaks near 1725 cm\({}^{-1}\) (v(C=O)) and 1 160 cm\({}^{-1}\) (v(C-O)) are assigned to the presence of triglycerides, basic constituents of the binding material. The relatively broad carbonyl band is arising from the contribution of oxidation products of triglycerides (aldehydes, ketones, and carboxylic acids). The band from 1600 cm\({}^{-1}\) (v(C=C)) is partly due to unsaturated triglycerides present in the binding materials. Because of the sample constraints mentioned previously, it is rather difficult to make unequivocal assertions about the organic substances present in the sample on the basis of the Raman spectra alone. The zinc ions from the pigments bind to the carboxylate ions in the polymerized oil network as an intermediate step in paint aging [69], a process in which the diffusion of metal ions and fatty acids takes place to explain the appearance of metal soaps in the paint structure oil. The use of a protein binder by master painters is demonstrated by the presence of linoleic, stearic, azelaic, and palmitic fatty acids, according to GC-MS measurements, Figure 7:0 Azelaic acid is a marker of the use of drying oil. Additionally, long-chain hydroxycarboxylic fatty acids could be derived from waves, such as beeswax, and has been used as a binder in a painting technique called encaustic. The use of a protein binder by master painters is demonstrated by the presence of linoleic, stearic, azelaic, and palmitic fatty acids, according to GC-MS measurements [70]. Monocarboxylic and dicarboxylic saturated fatty acids (azelaic and palmitic acid are the most abundant), indicate the presence of a lipid material, and are found in all the analyzed samples [71]. Phthalates are also identified in the chromatogram in Figure 13; they are a sign of the microbial population present in the painting layer. The peaks corresponding to phthalate derivatives can be easily observed in the investigated samples. Regarding the lipid content, palmitic acid, stearic acid, and azelaic acid, are present in all the analyzed samples, Figure 7:1 Special attention was paid to the determination of the azelaic acid content, because of its high level in the drying oil.