# Deterioration of White Tempera Mock-Ups Paints in a SO\({}_{2}\)-Rich Atmosphere
## 3 Results
### Pigment Characterization
On the other hand, the FTIR spectra of the rabbit glue binder showed bands at 3290 cm\({}^{-1}\) assigned to O-H symmetric stretching or/and N-H stretching from proteins, at 2871 cm\({}^{-1}\) assigned to C-H symmetric stretching, and at 1620 cm\({}^{-1}\) associated with C=O stretching from amide I. A band at 1520 cm\({}^{-1}\) assigned to C-N stretching and N-H bending from amide II was also found. Finally, bands between 1400 and 1000 cm\({}^{-1}\) were associated with collagen absorption features attributed to CH\({}_{2}\) wagging, CH\({}_{3}\) deformation, C-N stretching and C-O stretching [13; 31]. Regarding the reference paints, in the CA- and BSG-based paints, calcite was identified through their characteristic C-O bands: the most intense at 1409 cm\({}^{-1}\), and weaker ones at 874 and 725 cm\({}^{-1}\) assigned to CO\({}_{3}\)\({}^{2-}\) stretching [32]. Compared to calcite, dolomite displayed characteristic FTIR absorption bands at 3020, 2626 and 730 cm\({}^{-1}\)[33]. Surprisingly, although dolomite was identified in the reference CA-EF-E paint by using XRD, the FTIR analysis did not allow the detection of the aforementioned bands assigned to this mineral. Portlandite was identified by XRD in several reference and aged mock-ups (Table 1). In the FTIR spectra, the presence of this mineral was confirmed through a strong band around 3680 cm\({}^{-1}\), which was assigned to O-H stretching vibration of portlandite [34]. Figure 6: FTIR (absorbance) spectra of the reference (-Ref) and aged (-SO\({}_{2}\)) mock-ups. Check Table 1 for the identification code of samples. (**A**) Egg-yolk-based paints, (**B**) Rabbit glue-based paints. In red, new FTIR bands, not present in the reference samples, are indicated. Letters between brackets, a: anhydride, b: bassanite and g: gypsum. For the reference G-based paints, the sulfate ion (S-O) of gypsum was detected through four fundamental vibration modes: bands \(\sim\)980 cm\({}^{-1}\) due to SO\({}_{4}\)\({}^{2-}\)\(v_{1}\) symmetric stretching vibration, \(\sim\)450 cm\({}^{-1}\) due to SO\({}_{4}\)\({}^{2-}\)\(v_{2}\) symmetric bending vibration, \(\sim\)1100 cm\({}^{-1}\) for SO\({}_{4}\)\({}^{2-}\)\(v_{3}\) symmetric bending and \(\sim\)610 cm\({}^{-1}\) for the SO\({}_{4}\)\({}^{2-}\)\(v_{4}\) asymmetric bending vibration [35; 36]. Considering the diverse calcium sulfate minerals (gypsum, bassanite and anhydrite), small shifts can be found among the FTIR spectra bands [36]. The SO\({}_{4}\)\({}^{2-}\)\(v_{1}\) vibration was found at 1017, 1015 and 1008 cm\({}^{-1}\) for anhydrite, bassanite and gypsum, respectively, being more intense in bassanite and almost inappreciable in anhydrite [36; 37]. Gypsum, bassanite, and anhydrite all exhibited a doublet for the \(v_{2}\) symmetric bending of the SO\({}_{4}\)\({}^{2-}\) tetrahedra at 439 and 415 cm\({}^{-1}\), 489 and 427 cm\({}^{-1}\) and 499 and 416 cm\({}^{-1}\), respectively. The SO\({}_{4}\)\({}^{2-}\)\(v_{3}\) symmetric bending was identified through two bands at 667 and 595 cm\({}^{-1}\) for gypsum, at 659 and 594 cm\({}^{-1}\) for bassanite and three bands at 672, 610 and 591 cm\({}^{-1}\) for anhydrite [37]. For the \(v_{3}\) antisymmetric stretching vibration, the strongest absorption peaks were found at 1111, 1102 and 1094 cm\({}^{-1}\) for bassanite, gypsum and anhydrite, respectively [37]. For the \(v_{4}\) antisymmetric bending vibration modes, the identified bands were those at 676, 629 and 612 cm\({}^{-1}\) in anhydrite, 668 and 628 cm\({}^{-1}\) in bassanite and 670 and 620 cm\({}^{-1}\) in gypsum [37]. Additionally, we found (i) for gypsum, O-H stretching vibrations at 3500 and 3394 cm\({}^{-1}\) and O-H bending vibration at 1680 and 1619 cm\({}^{-1}\), and (ii) for bassanite, O-H stretching vibrations around 3600 and 3540 cm\({}^{-1}\) and O-H \(v_{1}\) bending vibration at 1617 cm\({}^{-1}\)[37].