Cambridge: Butterfly colours could be use to make bank notes harder to forge

Research lead

Scientists at Cambridge University have discovered a way of mimicking the bright colours found on the wings of tropical butterflies and say the findings could have applications in the security printing industry, helping to make bank notes and credit cards harder to forge.

The striking iridescent colours displayed on beetles, butterflies and other insects do not rely on pigments, but are produced by light bouncing off microscopic structures on the insects' wings.

The researchers studied the Indonesian Peacock or Swallowtail butterfly (Papilio blumei), whose wing scales are composed of intricate, microscopic structures that resemble the inside of an egg carton. Because of their shape and the fact that they are made up of alternate layers of cuticle and air, these structures produce intense colours.

Using a combination of nanofabrication procedures, including self-assembly and atomic layer deposition, the researchers made structurally identical copies of the butterfly scales, and these copies produced the same vivid colours as the butterflies’ wings.

“Although nature is better at self-assembly than we are, we have the advantage that we can use a wider variety of artificial, custom-made materials to optimise our optical structures,” said researcher Mathias Kolle.

As well as helping scientists gain a deeper understanding of the physics behind these butterflies' colours, being able to mimic them has potential applications in security printing.

“These artificial structures could be used to encrypt information in optical signatures on banknotes, or other valuable items, to protect them against forgery. We still need to refine our system but in future we could see structures based on butterflies wings shining from a £10 note or even our passports,” says Kolle.

The butterfly may also be using its colours to encrypt itself, appearing one colour to potential mates but another colour to predators.