## 3 Results
### Pigments
#### 3.2.2 Green  
The analyses of green hues revealed a frequent use of viridian, often in combination with ultramarine, Prussian blue, yellow iron-rich earth pigments and yellow chromate pigments. Sample 4, taken from the green paint of _Countryside in China_ (1933) was found to contain a high concentration of viridian. The pigment was confirmed by IR absorption peaks at 3083, 1285, 1252, 1064 and 794 cm\({}^{-1}\). The result was consistent with the PLM observation and SEM-EDS analysis. However, an unequivocal declaration of the presence of viridian in other green paint mixtures was challenging due to overlapping bands of other compounds. Besides viridian, emerald green is another green pigment used. However, it was found only in two investigated green paint mixtures--samples 3 and 4, extracted from _Countryside in China_ (1933). This pigment was evidenced by the coincident presence of copper and arsenic elements (Figure 10) as well as IR absorption peaks in the region 1555-1530 cm\({}^{-1}\) and ca. 680 cm\({}^{-1}\) and 630 cm\({}^{-1}\)[29]. Minor use of this green pigment by [PERSON] was already reported in the research of his Paris painting practice (1929-1932) and paintings from the 1950s, suggesting a reluctance to give it a more pronounced role [28; 30]. Figure 8: Microscopy image (**a**), corresponding SEM-EDS elemental map (**b**) and SEM-EDS spectra (**c**) of sample 6, extracted from _Seaside_, 1936. The SEM-EDS analyses show the distribution of S elements relating to ultramarine, Cr relating to viridian and Fe attributing to yellow iron-containing earth in the paint sample. A green hue of sample 10 extracted from _Backyard_ (1934), was achieved by mixing ultramarine, some Prussian blue and strontium yellow. The latter was verified by the SEM-EDS detection of Cr and Sr elements and FTIR absorption peaks at 903, 881, 873 and 840 cm\({}^{-1}\) (Figure 11). Prussian blue was suspected based on the PLM characterisation of the particles, followed by trace Fe-signal and an IR absorption peak at 2089 cm\({}^{-1}\), whereas ultramarine was assumed based on strong S-, Na-, Si- and Al-signals, an IR absorption peak at 1000 cm\({}^{-1}\) and PLM observation. The microscopic image of the paint cross-section shows partially mixed pigments allowing us to infer that the green was obtained on the palette by the artist (Figure 12). Figure 10: Optical microscopy image of the paint cross-section of sample 3 obtained from _Countryside in China_, 1933 and captured at 100\(\times\) magnification (top-left), followed by SEM-EDS elemental distribution maps. The intensity of the signal of each element is represented by a range of grey tones: white represents high intensity and black represents low intensity. A concomitant presence of highly intensive copper and arsenic signals suggests the use of emerald green. Figure 9: Detail of _Working in the fields_, 1933, photographed in VIS showing the location from which sample 3 was extracted (**a**) and IRFC image of the same area (**b**). SEM-EDS spectra of the blue paint, extracted from the sampling spot (**c**) and corresponding optical microscopy image of the cross-section of sample 3 at 200\(\times\) magnification with the marked area of analysis in layer 2 (**d**). A blue colour recorded as dark violet in IRFC (**b**) and the presence of Fe and Cr (**c**) in layer 2 (**d**) suggested a mixture composed predominantly of Prussian blue and viridian. A combination of Prussian blue and yellow chromate pigment(s) is assumed in some green paint samples. Although Prussian blue was positively identified with FTIR, a precise attribution of yellow chromate pigments was challenging due to their overlapping bands and signal interferences of other compounds. For example, FTIR of the green paint in sample 4 from _Sensible_ (1936) implies the presence of zinc yellow (PY36) (937, 872 and 820 cm\({}^{-1}\)), chrome yellow (PY34) (839 and 820 cm\({}^{-1}\)), barium yellow (PY31) or strontium yellow (872 and 839 cm\({}^{-1}\)), chalk (PW18) (872 cm\({}^{-1}\)) and viridian (797 cm\({}^{-1}\)).