Butterfly Wing Colours May Reduce Bank Fraud

I love that headline.

From ScienceDaily, reporting on an article in Nature Nanotechnology last month, is a story about how some of nature’s colours have provided the inspiration for a potential source of encryption. You may have seen visual devices on bank notes – little holograms, for instance. These are difficult to reproduce without very specialised equipment, which makes it harder for counterfeiters to ply their fakery.

Harder, but not impossible. So those responsible for coming up with technical tricks to protect money are always looking for new, harder-to-copy methods for creating these sorts of identifying devices.

And nature has given them an idea for one: iridescence, which is when things – like butterfly wings, beetle shells, and the inside of seashells – appear to change colour when you view them from different angles.

Iridescence happens when something is made in layers that are translucent(that is, some light can pass through them), and usually with tiny structures in the layers. Light goes through the top layer, some of it bounces back out (at angles depending on the tiny structures) but some of it goes down to the next layer, where some of it bounces back out but some of it goes down to thenext layer, etc. But all of those reflections interfere with each other, and their frequencies are shifted with respect to each other, and they reflect differently off different bits of the tiny internal structures. Bottom line: the colours reflecting from objects made like this appear differently when viewed from different angles.

According to that article, a team have succeeded in artificially creating layers of material with those little microstructures. It’s a very complicated bit of nanotechnology to do so, and the end result could be a device that could more securely mark legit currency.

Thanks for the idea, nature.