Coloured pastes are loaded into the tube separately but are not stored in compartments. The pastes are designed to have just the right viscosity or thickness so that they don’t mix, acting like solids inside the tube but flowing smoothly when you squeeze or pump it.
They have similar flow characteristics to ketchup, which only gets moving with a good shake or a squeeze.In some toothpastes, anozzle at the top of the tube has separate holes for different colours, ensuring they emerge as neat stripes.
Read more:
- How is caffeine removed from decaffeinated coffee?
- Does an apple a day keep the doctor away?
- How to make the perfect cup of tea
Asked by: Tina Chapman, Colchester
To submit your questions email us at questions@sciencefocus.com (don't forget to include your name and location)
- This article first appeared inissue 374ofBBC Science Focus Magazine–find out how to subscribe here