Dear Teddy & Koko
How do toothpaste makers get the stripes in toothpaste? And why do they persist until the tube is used up?
Miles Ellingham, London, UK
Surely the different coloured pastes are forced into the tube at the same time, and most likely, the tube is unsealed when this takes place allowing easy access of paste. When the tube is squeezed, naturally the paste exits it in the same manner in which it entered.
The tubes for these toothpastes are specially designed.
The nozzle of the toothpaste tube doesn't end at the 'reservoir' - it is actually a pipe which extends a short way in. At the nozzle end of this tube are two holes located on opposite sides. Either side of the tube are the striping substances in their own seperate reservoirs. When you squeeze the tube, the white paste travels up the pipe, and as it passes the holes in the pipe, it picks up the striping substances and carries them out through the main nozzle. You will note that the stripes are 'stuck' to the outside rather than running through the toothpaste proper.
For a diagram and further explanation see http://www.bbc.co.uk/dna/h2g2/A1047836
Tina "Mainframe" Cassidy:
I'm not entirely sure if my information is correct on this matter, but I was talking to my boyfriend the other day and the colours of toothpaste was mentioned.
He told me that the reason that the toothpaste was able to stay separate within the tube its self no matter how much you play with it is to do with the density of the individual colours to begin with. The main colour of the paste has a higher density than the other colours, and depending upon the other colours depends on the individual densities.
As I said previously I'm not entirely sure if I was told a pack of lies to shut me up for 10 minutes while I could think about the possibility of it being true.
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