## 3 Results
### Pigments
#### 3.2.4 White and Black  
The SEM-EDS elemental analyses of white paint samples revealed high concentrations of Zn coexisting with Ba and S elements, suggesting the use of lithopone (PW5) and/or barium white (PW21) and zinc white (PW4). The Zn element is commonly present in other investigated paint mixes; however, it is difficult to ascertain whether zinc white was used or whether zinc was present as part of the lithopone added by the manufacturer as an extender. Interestingly, an exclusive presence of zinc white was recorded in the white paint (sample 3) from _Seaside_ (1936).  
Low concentrations of Pb found in almost all investigated white paint samples may be indicative of trace presence of lead white (PW1). Frequent admixtures of lead white to zinc-based white paints may relate to the commercial modification of the latter. As zinc white is characterised by poor hiding power in the oil binder, manufacturers often employed lead white or titanium white to improve its properties [35]. Based on the SEM-EDS analyses, lead white features as the main compound only in the white paint (sample 5) from _Countryside in China_ (1933). This finding was corroborated with the UVR imaging of the sampling area, which appears white, indicating highly reflective lead white (Figure 14) [12,13,15].  
Figure 14: VIS (**a**) and corresponding UVR detail image (**b**) of _Countryside in China_, 1933, indicating a strong UV reflectance of white paint from the building (red arrow), suggesting a presence of lead white and/or lithopone.  
Figure 13: ATR–FTIR spectra of the brown paint of sample 11, extracted from _Working at the fields_, 1933, with labelled marker peaks of upper and reference spectra of the same pigment.  
Frequent occurrences of chalk at low concentrations were suspected based on the detection of Ca element. The presence of chalk may suggest its commercial use as an extender to other white pigments [36]. The detection of Ti only in the white paint (sample 14) from _Waterfall_ (1936) seems to point to the minor addition of titanium white (PW6). This white pigment is known to be used as a commercial admixture of zinc white, barium white or lithopone to improve their properties [37]. According to the 1934 W&N catalogue, titanium white was extended with barium white (Appendix A, Figure A1), which is also present in the analysed sample. However, Lefranc listed this white pigment as pure titanium dioxide in the 1934 catalogue (Appendix A, Figure A3), whereas R&S did not sell it in the 1930s (Appendix A, Figure A2) [37]. Although titanium white was found in a single white paint sample, the SEM-EDS analyses lead us to believe that this pigment may be present in small amounts in other investigated colour mixtures. However, it is also known that titanium is a frequent impurity in mineral-based pigments [37].  
Black brushstrokes were observed only in _Chinese house_ (1934). The analyses of sample 5 from that painting revealed that instead of pure black pigment, the paint was composed of a mixture of Prussian blue, ultramarine, viridian and some bone black. The minimal admixture of bone black was suspected in other paint mixes to modify their shade.