Inspired by a butterfly whose wings appear to change colours, researchers from Harvard University have found a way to mimic the colour change using artificial materials to build a new counterfeit-proof material.

The material can be used to make more secure banknotes or passports.
The superthin, transparent material is made of a series of microscopic plates. Each tiny plate, about 18 mm tall, features a ridged edge.

By changing the height size and spacing between the plates or the ridges, the researchers can change how the material diffracts light.

"We thought there could be some benefit for such a unique material in security printing. The material could also coat the solar panels to manipulate how light enters the individual cells," explained study co-author Mathias Kolle from Harvard.

The male Pierella luna butterfly from Latin America has wings that appear to change colour when looked at from different angles.

The optical trick is possible thanks to tiny scales on its wings that curl slightly upward at the end and diffract light, Live Science reported.