Figure 6

Raman spectra recorded on pigment and plaster samples, (a): red pigment (haematite) (0.5 mW, 5 scans of 20 s), (b): yellow pigment (goethite) (0.5 mW, 5 scans of 50 s), (c): black grain in yellow pigment (carbon black) (0.1 mW, 10 scans of 20 s), (d): black pigment (carbon black) (0.1 mW, 10 scans of 20 s), (e): preparation layer (gypsum) (1 mW, 10 scans of 20 s), (f): plaster layer (quartz + gypsum) (1 mW, 10 scans of 20 s).