Fig. 7

Identification of the blue colorant: a colour image of ‘Area 37’ on the Selden map (Fig. 1) derived from PRISMS data using CIE (Commission Internationale de l´Eclairage) standard D65 illumination and the 2 degree standard observer; the white circle marks the position where the reflectance spectrum was extracted and b near infrared 880 nm PRISMS image; c the reflectance spectrum extracted from the dark blue area (black crosses in the spectrum) is fitted by the KM model using a reference spectrum of indigo (blue circles)