Combating counterfeiters could soon be as easy as breathing

Researchers at the University of Michigan have developed an iridescent material that reveals hidden words or images in the right setting. What exactly causes the message to show? A single breath. That’s right, breathing on the plastic sheets makes whatever has been inscribed on it visible — thanks to a little instant humidity — but otherwise hidden from view. Images are created using a custom ink-jet printer to output a water-repellant coating in the desired shape. When breathed on, water condenses to show the image — similar to the manner in which a peacock’s feathers lose their glimmer when they’re wet.

http://www.engadget.com/2014/08/08/counterfeit-detection-by-breathing/