Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: EvaH on 16/04/2020 10:10:23
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Jan wants to know:
Why is the foam is always white? No matter what color soap I use (red, purple, even black shampoo), when I spread it around the foam is always white.
What do you think?
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If you can create a single large bubble, you can often see rainbow-hued interference bands in the bubble wall.
When you have very many bubbles together, they reflect light of all wavelengths in all directions.
- A mix of all possible colors is seen as "white" light
- This is the same effect as seen in white clouds and snow
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Bubbles are bounded by a thin film of liquid that is essentially colourless and transparent, so most of the light from each bubble is passing through it rather than reflected off it, and they appear white not because they are white, but because they're scattering white light. Perhaps if you could find a liquid which is sufficiently opaque that the light transmitted is less than the light reflected it might be possible to dye it and get coloured suds. Milk perhaps? Come to think of it, the bubbles in an Aero chocolate bar are brown, not white.