# Deterioration of White Tempera Mock-Ups Paints in a SO\({}_{2}\)-Rich Atmosphere
## 3 Results  
### Pigment Characterization  
XRD confirmed that the mineralogical composition of the white pigments differed to that reported by the manufacturer (Table 1); a similar finding was obtained in [24]. The exception was for Bianco di San Giovanni pigments (BSG-ST and BSG-C) which were composed by portlandite (Ca(OH)\({}_{2}\)) and calcite (CaCO\({}_{3}\)) as informed by the manufacturer. CA-EF pigment was composed of calcite, though dolomite (CaMg(CO\({}_{3}\))\({}_{2}\)) was identified as an impurity; a similar finding was reported in [6]. In gypsum pigments G-EF and G-F, rather than gypsum (as reported by the manufacturer), bassanite (CaSO\({}_{4}\)\(\cdot\)1/2H\({}_{2}\)O) and anhydrite (CaSO\({}_{4}\)) were identified (Table 1). Bassanite was present in GM (accordingto the manufacturer), however anhydrite was also identified. LW pigment, which is sold as basic lead carbonate (Pb(CO\({}_{3}\))\({}_{2}\cdot\)Pb(OH)\({}_{2}\)), is actually composed of hydrocerussite (2 PbCO\({}_{3}\cdot\)Pb(OH)\({}_{2}\)) and cerussite (PbCO\({}_{3}\)), as reported in the literature [25]. Regarding the pigments' grain size, some inaccuracies were found between values reported by the manufacturer and the experimental data (Table 1), as found elsewhere [13; 18; 19]. For example, for pigment CA-EF, a grain size of 20 \(\upmu\)m was reported by the manufacturer, while the laser diffraction detected a maximum particle size of 25 \(\upmu\)m and a range from 0.25 to 100 \(\upmu\)m. Moreover, it is noticeable that for pigment BSG-C, we detected a grain size range between 0.3 and 250 \(\upmu\)m whereas the manufacturer stated a range between 120 and 1000 \(\upmu\)m. In the case of gypsum pigments, differences with the sizes reported by the manufacturer were also detected. For the G-EF pigment, a grain size lower than 75 \(\upmu\)m was reported, while a maximum grain size of 7 \(\upmu\)m and a range from 0.2 to 85 \(\upmu\)m were experimentally obtained. For the G-F pigment, the grain size stated by the manufacturer was lower than 32 \(\upmu\)m while the size range here found was from 0.2 to 75 \(\upmu\)m, with a main maximum particle at 9 \(\upmu\)m. For the G-M pigment, a grain size lower than 40 \(\upmu\)m was reported by [PERSON] while the real maximum grain size was 16 \(\upmu\)m, with the range between 1 and 160 \(\upmu\)m. Likewise, for pigment LW, the manufacturer indicated a grain size lower than 45 \(\upmu\)m, although the primary particle size was 3 \(\upmu\)m with a size range from 0.1 to 10 \(\upmu\)m.  
Physical, Mineralogical and Chemical Changes of the Mock-Ups After SO\({}_{2}\) Exposure Aging Test  
Stereomicroscopy observations made on the paintings before being tested revealed an influence of the grain size on the roughness of the paints, since paints made with coarser pigments had rougher surfaces (Figure 1). For example, the surfaces of BSG-C-based paints showed greater irregularity since the pigment used was the coarsest. The paint surfaces showed surfaces with circular pockmarks, assigned to relics of air bubbles. Moreover, in LW-E paint, where the pigment had the smallest grain size (3 \(\upmu\)m), it was possible to see the brush strokes (Figure 1). On the other hand, some paint mock-ups containing egg yolk often showed a higher yellow coloring (due to the binder tint) than their counterparts made with rabbit glue. (See Figure 1, CA-EF-E, BSG-ST-E, BSG-C-E, G-EF-E, G-F-E). The SO\({}_{2}\) aged paints did not show any visible modification of their surfaces in comparison with the reference paints (Figure 1). However, the spectrophotometry results (Figure 2) revealed that some paints (i.e., CA-EF-E, BSG-ST-E and G-F-R) suffered \(\Delta E^{*}{}_{ab}\) higher than 3.5 CIELAB units, which is the threshold above which a color change is visible by a non-expert observer [26]. Therefore, considering \(\Delta E^{*}{}_{ab}\), the aged paint CA-EF-E showed the highest color change, while the aged paint G-M-R showed the lowest color change.