3.1.7. Green Gouaches

Three distinct green gouaches were used in *Jazz*, a darker (G1), a lighter (G2) yellowgreen, and a teal green (G3) that appears streakier. G1 and the lighter G2 both contained Hansa Yellow 10G (PY3), a yellow pigment with a greenish tint, and phthalocyanine green (PG7). The two are often found combined in yellow-greens [48]. PG7 was observed in confocal and p-Raman [49] (Figure S13) and detected by p-XRF through the presence of Cl and Cu peaks (Figure S14), though not confirmed by FTIR [17,50]. Conversely, PY3 was more readily observed by μ- and (non-KK transformed) r-FTIR [17] (Figure S15) than by Raman [49] spectroscopies, emphasizing the advantage and necessity of complementary techniques. The green gouache was applied on top of the gray background in P17 and P19, and both p-Raman and r-FTIR detected a signal from underlying pigments. G3 contains PG7 and ultramarine blue. Both pigments were confirmed by p-XRF and Raman. Some of the PG7 bands were weakly detected by μ-FTIR.

#### 3.1.8. Yellow Gouaches

A total of seven different yellows (Y1 to Y7) were identified across twelve prints, with tonalities varying from light green-yellow to dark orange-yellow. Several prints present both a lighter and a darker yellow. All the pigments were identified as Arylid Hansa yellows, by themselves or combined: green-yellows PY3 and PY5 (Hansa Yellow 5G); red-yellows PY6 (Hansa Yellow 3G) and PY10 (Hansa Yellow R). It is notable that PY5 and PY10 are no longer in production [41]. All were easily identified by μ-FTIR and by r-FTIR when sufficiently abundant (Figures S16 and S17) [17], and/or confocal and p-Raman (Figures S18 and S19) [49]. Cl is a constituent present in most of these monoazo yellows and was detected by p-XRF (Figure S20). A small amount of lead chromate was seen in Y5 as confirmed by p-XRF (Cr, Pb) and μ-Raman (Figure S21) [31].
