Counterfeiters be warned: banknotes may soon be harder to fake thanks to a new iridescent film that changes colour when you turn or twist it.
The polymer film mimics the structure of naturally occurring opals (pictured) and could be used to make eye-catching paint that shimmers when viewed from any direction, or food packaging that changes colour if its contents spoil.
Butterfly wings and opals have already inspired the creation of make-up and paints with the same flickering, iridescent colours. These qualities spring from photonic crystals, whose micro-spheres sit in a three-dimensional repeating pattern, similar to a stack of…
