Fig. 9

a A detail of the colour image derived from the spectral image cube of ‘Area 12’ on the Selden map in Fig. 1 (the white circle indicates the position where the spectrum was extracted); b the reflectance spectrum extracted for the red area (black crosses) fitted with the KM model using a reference spectrum of vermilion (blue circles); c Colour image derived from the PRISMS image cube of ‘Area 25’ on the Selden map (the white circle indicates the position where the spectrum is extracted) and d the reflectance spectrum extracted from a dull red area (black crosses) fitted with the KM model using as reference pigments vermilion and indigo (blue circles)