Secure printing with water-based invisible ink
Researchers in China have developed a rewriteable paper coating that can encrypt secret information with relatively low-tech invisible ink—water. A message printed out by a water-jet printer on a manganese-complex-coated paper is invisible to the naked eye, but the message reveals itself under 254 nm UV light. The paper can be ready for another round of printing after erasing the message by heating it with a blow dryer for 15-30 seconds. The method, presented September 25 in the journal Matter, allows reversible secure printing for at least 30 cycles.