Pre-school day: mixing colours

Cute little girl with painted hands.

We all know what you get when young children mix paint: every possible shade of… brown. I don’t really understand brown – one of the most common colours on earth, and I can’t quite work it out.

Colours of paint absorb some colours of light and reflect others. White light is made up of a whole spectrum of colours, the result of different lengths of light waves. Blue objects reflect blue light and absorb everything else. Red things reflect red light and absorb everything else. But the spectrum doesn’t include brown. You don’t get brown light. Mix green light and red light and you get yellow. Mix all the colours of light and you get white. So how can we see brown?

Mixing coloured liquids at Life Science CentreOn a computer or phone screen, all of the colours are made by little rectangles of red, green and blue. The other colours aren’t really there at all – there is no pink, or brown, or yellow. The blobs are so tiny that our brains interpret a combination of hundreds of rectangles as a single colour, and with the right proportion of red, green and blue you can make anything. If you get the chance to put a phone screen under a microscope, you’ll see what I mean. This is additive colour mixing – the colour is made by adding together light of different wavelengths.

Paints or ink are a bit different. They use subtractive colour mixing. It’s all about what light is absorbed. Red absorbs everything but red. Green absorbs everything but green. Mix the two together, and we should be absorbing everything, right? So why do I get brown, not black? I think the answer here is that it’s never that perfect. We’re seeing some red reflected and some green reflected, and maybe even a trace of blue, and the whole mulch comes out as brown. The conclusion I draw from this is that I still don’t fully understand brown.

Let your toddlers play with mixing coloured liquids this pre-school day, and if you come up with a better explanation of the inevitable final product, let me know!

Come along and play this pre-school day! Tuesday 20 June, 9.30am – 3.00pm

Pre-school day

About Naomi Foster

I'm a Public Engagement Officer. My job involves developing science shows and public workshops, organising lectures for big people and our preschool days for little people. Any excuse to play! I'll be keeping you posted about some of the things I've got coming up.
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