Fig. 5

Raman spectra of the naphthol reds analyzed in the prints. A Raman spectrum (a) obtained from a red area in a print dated 1894. Signals of reference cotton scarlet (c) were detected. B Raman spectrum (a) obtained from a red area in a print dated 1897. Signals of reference brilliant scarlet (c) were detected. Due to the high fluorescent background, the spectra (a) have been background subtracted (b). C Close-ups (10× magnification) of a red area printed with cotton scarlet: the colorant has bled through the paper and it is visible on the verso (right)