The invention relates to a printing method according to which, during the printing process, one or more narrow nozzles eject a printing liquid, and to a printing liquid suitable for such a method. The invention is particularly suitable for forgery-proof printing on papers or articles. According to the invention, the printing liquid contains nanoparticles that can be induced to fluoresce or phosphoresce. Said nanoparticles are small crystalline particles that can be induced to fluoresce or phosphoresce on their own or when mixed with dopants. Individual dots (10, 12) can be printed by means of a printing liquid that contains said nanoparticles. Due to their small size of from 1 to 1000 nanometers, preferably in the range of 300 nanometers or even much smaller depending on nozzle diameter, there is no risk of very narrow ink jet nozzles getting plugged. The induction and fluorescence emission frequency ranges are narrow-band so that for a security control of the print the respective wavelength-specific induction or detection is required, thereby increasing protection against forgery.