Fig. 3.

(a) Ignition time (seconds) of paper stripes impregnated with sepia ink at different concentrations (circles and squares). Papers were air dried, and then irradiated with 808-nm laser for different times. The higher the ink content, the faster the paper ignition. Note that even low ink concentration lead to ignition after 5 s, proof of its very high photothermal efficiency. (b) Temperature increase (in °C) of water (squares) and 50% sepia ink in water (circles) during 808-nm irradiation for different times (min). The temperature increases significantly for the sepia ink solution (58 °C at 4 min), while the temperature remains constant for water alone (26 °C at 4 min).