Fig. 6.

(a) Normalised photoacoustic spectra (symbols) and corresponding normalised optical absorption spectra (solid lines) for four gel wax compounds that contained carbon black ink and coloured inks (green, blue, and violet). Each compounds also contained TiO₂. For each composition, spectra were normalised to the maximum value of the photoacoustic spectrum. (b) Normalised photoacoustic signal amplitudes from 20,000 excitation pulses, which indicated good photostability.