*3.2. Characterization of the Fresh Paint*

The paint film prepared from Golden Heavy Body Artist Acrylics in C.P. Cadmium Orange is uniformly orange in color with no obvious inclusions. Elemental analysis by XRF of the cadmium orange paint confirmed the presence of cadmium (Cd), sulfur (S) and selenium (Se), consistent with the cadmium orange pigment. Barium (Ba) and zinc (Zn) were additionally identified in the paint.

The Raman spectrum of the cadmium orange paint (Figure 4a) contains bands assigned to the longitudinal optical (LO) phonon and overtone (2LO) of CdS at 296 and 595 cm−1, respectively. The LO phonon for CdSe is typically observed at around 200 cm−<sup>1</sup> but may shift in wavenumbers based on the pigment composition, and as such may be accounted for by either or both of the peaks at 192 and 214 cm−<sup>1</sup> [21]. The presence of barium sulfate, identifiable in Figure 4a by the peak at 988 cm−<sup>1</sup> representing the symmetric stretching of the SO4 group, indicates that the paint contains the lithopone version of cadmium orange [16]. The mineral form of zinc could not be identified from analysis, however, the identification of lithopone may suggest the presence of zinc sulfide (ZnS) and the UV fluorescence observed in the paint, discussed below, may be attributed to the presence of zinc oxide (ZnO).

**Figure 4.** Raman spectra obtained from (**a**) fresh C.P. Cadmium Orange acrylic paint (Golden Heavy Body Artist Acrylics) and (**b**) fresh Titan Buff acrylic paint (Golden Heavy Body Artist Acrylics).

The cadmium orange paint has the same distinct green UV fluorescence visible in the cross-section images shown in Figure 2c,d. The fluorescence occurs from very fine particles distributed evenly throughout the paint matrix. Multiple cadmium orange reference samples and pure barium sulfate displayed no fluorescence under the same UV conditions. A reference sample for lithopone contained a scattering of particles which fluoresced pale yellow, typical of zinc oxide (ZnO). Zinc oxide may be present in lithopone in trace amounts, and whilst the fluorescence of zinc oxide is not a match for the green fluorescence observed in the cadmium orange paint film, it is the only pigment identified to have a fluorescence that may be present. It is speculated that the fluorescence color has altered as a result of the paint preparation, however, further study is required.

The paint film prepared from Golden Heavy Body Artist Acrylics in Titan Buff is off-white in color and includes both red and black inclusions. XRF analysis of the paint film showed the presence of titanium (Ti) and Raman analysis identified the presence of rutile (titanium dioxide, TiO2), based on the presence of B1g, Eg and A1g Raman active modes of the of the rutile single crystal at 142, 446 and 610 cm−1, respectively (Figure 4b) [22]. The red and black inclusions were identified as hematite (Fe2O3) and rutile, respectively, with Raman. The identification of rutile in the black inclusions suggests the use of the natural form of the mineral in addition to the white synthetic form used for the bulk of the paint [23].

Importantly, no Cl was identified in either of the paints, supporting the theory that residual chloride ions in the terracotta are involved in the observed alteration of the paint. FTIR analysis confirmed the presence of an acrylic binder in both the cadmium orange and Titan Buff paints, which was identified to contain a combination of methyl methacrylate, n-butyl acrylate and n-butyl methacrylate by pyrolysis-GCMS.
