YOU dip a plastic wand into a mixture of water and washing up liquid and raise it to your lips. With a gentle blow, you unleash a stream of bubbles that bob about in the air, winking a swirling rainbow of colours back at you as they reflect the light. This is the beauty of iridescence.
You can also see it on the wings of birds and the shells of beetles. It is a completely different way of creating colour than the pigments and dyes we typically load onto brushes and into printers, one that is more subtle and adaptable. Now, we are starting to get a deeper understanding of iridescence. We are learning that animals make use of it in surprisingly varied ways, and it seems we could soon join them in harnessing this phenomenon to pull a few tricks of our own.
Most of us think we know the basics of how colour works. A ray of white light, composed of many different wavelengths or colours, strikes an object. Some of the wavelengths are absorbed by pigment molecules and the remaining ones are bounced back and seen as a particular colour. All this is true – but it isn’t quite the full story.
Colour can also be produced by surfaces that reflect, or scatter, different wavelengths of light back in slightly different directions. This is what happens when we look at the surface of a bubble or a bird’s wing and see that characteristic iridescent shimmer. If you move your eyes, the colour of the surface seems to shift and dance. The reflections are caused by tiny structures – …