Fig. 2

a Visible light detail of the Girl’s face. René Gerritsen Art & Research Photography; b Map of fluorescence spectral endmember (‘blue’) showing red lake fluorescence obtained with UV excitation source. The corresponding first derivative endmember spectrum used for the map is shown in f; c MA-XRF map of potassium (K K); d Map of two fluorescence spectral endmembers (‘red’ and ‘pink’) showing red lake fluorescence obtained with excitation at 460–532 nm. The corresponding first derivative endmember spectra used for the map are shown in g; e average fluorescence spectra of the same pixels used to define the ‘blue’, ‘red’, and ‘pink’ first derivative endmember spectra