Ever wondered if you could permanently change your hair colour with just the sweep of a flat iron? Well, probably not, but new researched published this week by Prof. Zeyd Leseman et al. at the University of New Mexico suggests that one day you may be able to do just that.

The paper, entitled 'Nano-Patterning of Diffraction Gratings on Human Hair for Cosmetic Purposes', is the result of experimentation with Focused-Ion Beam (FIB) technology to etch the hair surface into a diffraction grating, allowing certain wavelengths from incident light to scatter and the hair surface to reflect any colours from the visible spectrum.

Confused? Let's break it down...


What is a diffraction grating?

More often than not, the colours you see around you are the result of molecules called chromphores. These molecules are able to absorb certain wavelengths from the light source you see by (known as incident light), reflecting back only the wavelengths your eyes interpret as its colour. So, the chromophores in paint on a red car will absorb most of the orange, yellow, green, blue and violet wavelengths and reflect mostly red ones back. This is how modern hair dye works. We trap molecules in the hair that are made up of chromophores that reflect the colour we want the hair to be.

But not all colour is the result of these molecules:


Yep - the tail feathers of a peacock and the wings of butterflies are actually not the colours they look. They aren't the result of pigmentation and chomophores. No, these molecules are instead called schemochromes. Rather than absorbing and reflecting  wavelengths, schemochromes make up collagen strugtures that diffuse and refract light in such a way that we see the colours we do. This is called structural coloration - think of the glass prism experiment you did in school, and you're along the right lines. This light scattering is the reason that the above creatures have more of a shiny, iridescent look, and why we see them as so beautiful.

A diffraction grating is simply a type of structure that does the same thing. Tiny grooves in the grating are able to interfere with the very light waves that pass through it, showing either the entire spectrum, or just the parts we want to see. Human hair keratin is actually colourless, and each hair is made up of a kind of keratin tube containing the naturally coloured pigment melanin, (which also determines our skin colour). In this study, that transparent outer layer (known as the cuticle) is used to form a natural diffraction grating on the hair surface.


How is this done?

Remember that Focused-Ion Beam (FIB) mentioned earlier? That's our method. Using a device to fire cationic Gallium (Ga+) ions at the hair surface, these tiny diffraction gratings were very precisely 'drawn' onto the cuticle, following two patterns, an Archimedian Spiral (a), and a Hyperbola (b).


(a) Archimedian Spiral diffraction grating


(b) Hyperbola diffraction grating

The original image used to create these pattern were 4096px wide, and yet resulted in the above patterns measuring roughly 0.1mm across. That makes each of these pixels only 24.4 nanometers apart. It's more precise than you can possibly visualise. Using x and y coordinates along with a 'dwell time' (how long the Ga+ ion beam stays in position on one pixel), complex 3D nano-patterns were created on the hair surface.


What do the results look like?

Like this:



The two reflections on the top hair strand to the left are the Archimedian Spiral pattern and the reflections on the bottom strand are the Hyperbola pattern.

Please, don't feel underwhelmed. It may look a little gritty and insignificant, but what you're seeing there are unadultered closeups of human hair with just 0.1mm patches of this diffraction grating - and those patches are gloriously iridescent. It's similar to the film you see on the bottom of a compact disc.


Great! When do I get to do this?

Hold on to your colourist for a little longer. This research proves that it can be done. They still haven't coated an entire human hair - let alone a full head of them - with these patterns yet; nor have they honed a way of giving really specific colour. At the moment, you go to your stylist and look through a book containing dozens of shades. Here we have the possibility of many, many more, but none of the patterns they require.

The flat-iron idea is also conjecture at this stage. It's one way these scientists are suggesting turning this into a more commercially-adaptable technique. That equipment is not yet a reality.


So, will it ever happen?

Well, we just don't know yet. It's certainly a huge breakthrough in potential. But if you're looking for a ray of hope, I'll give you a little one. This was funded by Procter & Gamble in 2011. That's the company that makes a thousand and one of your household products and, more importantly, Wella Professionals in-salon colour. Earlier this year, Wella released an innovative new colour system called Innosence, which ingeniously altered the normal precursor molecule that causes allergic reactions by placing a kind of molecular 'cap' on the part of the molecule responsible. That is not directly related to this, but it does show that if any company is going to be interested in cashing in on the future of hair colouring, this is the one.

So I would definitely keep your eyes peeled.


For more info in this research and to hear Prof. Leseman talk about the discoveries, visit the University of New Mexico webpage on it here: 
http://news.unm.edu/news/new-technology-allows-hair-to-reflect-almost-any-color