New material reveals hidden message when you breathe on it

Chemists from Belgium and China have produced a new material that changes colour under a flow of human breath. After a while, the colour returns to normal. This creates possibilities for encryption and anti-counterfeiting. Our clothes, food and everyday devices get their colour from dye or pigments that absorb light. These colours fade over time, as laundry detergent ads never fail to remind us. But a different, more lasting type of colour exists as well. Structural colours.