How do you get distinct lines in toothpaste?

26 February 2012

Question

Why when you squeeze a tube of toothpaste with the lines of seperate colours do the colours not smudge into each other? They always come out in perfect lines.

Answer

Dave - Essentially, it's by clever engineering. If you look carefully at the toothpaste, instead of making those beautiful swooshes of toothpaste which they always show on adverts, if you chop the toothpaste straight across, you'll see that the colours are only just on the surface. In the middle, it's all just normal white toothpaste. So, what they're actually doing is, in the nozzle, very close to nozzle which squirts the toothpaste out, there are other little nozzles attached to bags of colour - often several different nozzles attached to bags of colour. So when you squeeze a tube of toothpaste, it squeezes both the main toothpaste bit and those little bags. And so, as the main toothpaste comes out, the extra coloured bits get squeezed out on the outside and you end up with a white tube with little coloured bits around the outside.

Chris - If you don't believe us, cut a tube up and you'll see this marvellous bit of engineering for yourself. It was patented in America, I think, in the 1960s or the late '50s. They actually introduced that as a major selling point. I think Signal was one of the first brands to use it in this country.

Dave - Probably, I think it's based on a similar system for making icing. So you can get coloured icing outside and the boring white icing inside.

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