3.1.10. Red Gouaches

The FTIR (Figures S27 and S28) and Raman analysis suggested that four different reds (R1 to R4) were used. R1, R2, and R4 contained mainly Toluidine Red (PR3) [17,50] and PR49:2—also found in Pk2. The p-XRF detected the presence of small amounts of lead chromate (Pb, Cr) in R2, while vermilion (HgS) was detected in R1 (Figure S29), as confirmed by Raman (Figure S28) [30]. PR49:2 was the only pigment detected in the less orange-hued R3.

## 3.1.11. Brown Gouache

The brown gouache (Br) was only used in two prints, P2 and P20. The main pigment was a natural iron oxide with a high content of aluminosilicates (possibly Sienna) and was confirmed by the hematite bands in r-FTIR [33] and ochre bands in Raman [31]. The p-XRF analysis also detected a small amount of lead chromate aside from the iron oxides.
