One of the highlights of 2014 for me was a talk by Peter Vukusic of Exeter University at the Society of Cosmetic Scientist’s meeting on May Day near Oxford. It was about alternative ways of creating colours for cosmetics.
Traditionally cosmetic colours are derived from pigments. These work by absorbing most of the spectrum of white light and reflecting back a single colour. This is a pretty well established technology dating back to before people started writing history down and in all probability predating the emergence of humans in our current form. But it isn’t the only way to create colour. Bird’s feathers and butterflies’ wings use a different technique.
If you can create an ordered structure at about the wavelength of light, it can reflect light of different colours. The colours result from a process called interference and was first explained by Thomas Young. Put at its most simple, it is bit like pulling a comb through porridge to create a pattern that was not there before. In practice the production of these kinds of colours, which biologists call structural colouration is a subtle business that can produce all kinds of effects which it would be impossible to produce in any other way.
The most interesting property of structural colouration for cosmetic purposes is that it is capable of producing very virulent colours from very thin layers. This is indeed exactly what butterflies do. It also has the ability to produce iridescent effects. The traditional means to achieve iridescence is using mother of pearl, which is in fact another biological example of structural colouration. This effect has already been replicated in the form of precisely manufactured plastic sheets that can be added to products like nail polishes.
So the possibilities of butterfly wing cosmetic colours are already being exploited, and there are no doubt many more to come.