Science Interviews

Interview

Sun, 17th Dec 2006

The Science of Colour 2

The Dye Industry and How Hair Dye Works - Anna Lacey

Part of the show The Christmas Q & A Show

 

Anna - Last week, we had a look at colour vision, and the range of pigments found in the natural world. We humans have used colours from plants, animals and minerals to make dyes for centuries. But in order to achieve the fantastic array of hues we see in today's world, we needed a colour revolution. Here's Graham Alcock, from the Society of Dyes and Colourists.

Graham - The first man made dye was produced mainly by accident in 1856 by a gentleman called William Henry Perkin. There were certain chemicals readily available at that time, and they were using the chemistry of coal tar to try and produce a synthetic cure for malaria. In other words, synthetic quinine. And while he was actually trying to produce a synthetic quinine, he had many many failures. But what he did do was to produce one day, a black sludge in the bottom of a flask. He was going to clean it out, and to clean it out he put some alcohol in, shook it up, and he actually produced this beautiful purple colour. So he did some tests on pieces of silk and he found out that they were very fast. In other words they didn't fade in the sun, they didn't wash out etc. So he set up his own little factory. And along with his brother who was his business partner, they started to produce this purple dye which he called mauvine.

Anna - So can we still see this colour mauvine today?

Graham - You can't see the original mauvine because the original coal tar had masses of impurties in it, and the other chemicals they were using as well had lots and lots of impurities. And you can't recreate the impurities.

Anna - The success of mauvine, especially after being worn by Queen Victoria, sparked off competition across Europe. With chemists and industrialists vying to create new dyes that not only looked good, but didn't wash out. But what is it that makes a dye stick in the first place?

Graham - Each fabric will require a particular dye recipe, and also it will more often than not require a Mordent. Now a mordent is a chemical which opens the fibre and allows the dye to actually penetrate really deeply into it. And then it closes up again, which if you like grips it within the fibre and stops it from washing out and fading in the sun.

Anna - However clothes aren't the only thing to benefit from the dye industry. Hair dye is used by millions of people world wide, either to hide grey hairs, or just for a change. Hair itself is made of a protein called keratin, and consists of three main layers: the medulla in the centre, the cortex in the middle and a thin protective cuticle on the outside. But before we look at dyeing hair, where does natural hair colour come from? Here's the London College of Fashion's Judy Beerling.

Judy - Hair colour is actually determined by the pigment melanin, which is produced by cells called melanocytes, that are the base of the hair follicle. And there are two types of melanins: eumelanin and pheomelanin. And they have different colours. And it's the combination of those colours that actually gives you your unique hair colour.

Anna - Melanin is normally passed from the melanocytes, into the hair's cortex. But as we get older, the melanocytes stop working. This exposes the natural white colour of keratin, and the overall mixture of white and coloured hairs, gives the hair a grey appearance. But if grey's not really your colour, permanent hair dye can offer a solution.

Judy - Permanent hair dyes work by a mechanism whereby you mix something that gives you oxygen (in fact it's hydrogen peroxide) with another bottle of stuff contianing ammonia and these dye precursors as they call them. That ammonia has two purposes. It helps the hair to swell so those dye precursors can get into the hair, and it activates the peroxide to produce oxygen, which mixes with those dye molecules. The dye precursors are oxidised by the oxygen and you get slightly larger molecules which get trapped inside the cuticle of the hair. So you get something approaching natural colour in the hair.

Anna - So a guaranteed way to have grey-free hair. But there's another surprising beneficiary to this tale. Graham Alcock again.

Graham - In a royal procession in 1850 you'd have had to kill over 10 million insects to actually produce the dye to dye the uniforms of the people in the procession. So if nothing else, making man-made dyes certainly saved a lot of insects.

Anna - Next time, I'll be finding out how mauvine dyes lead to a headache cure, and how a spot of colour can be used to treat disease.

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