3.1.14. Gray Gouaches

Three different grays (Gy1 to Gy3) were distinguished. Gy1, used only in print P18, contained possibly zinc white and barium sulfate (based on the high Zn to Ba ratio detected by p-XRF—Figure S31) and/or lithopone, and a small amount of Prussian blue (confirmed by a very weak CN band in r-FTIR). Gy2, on the other hand, was mainly composed of titanium white in anatase form according to Raman analysis, and calcium carbonate confirmed by Raman and FTIR (and a small amount of zinc white and barium sulfate or lithopone). The gray tonality was due to the presence of ultramarine blue and Prussian blue in (Figure S23c), both confirmed by p-XRF and by Raman [31]. Gy3 was present in P9 and was similar to Gy2 in tonality and composition except for the presence of the zinc-based pigment.
