Field of Science

Bubbles bubbles: But why are they white?

Last night I got a very interesting 'tweet' from a friend wondering why the 'blue' liquid 'bubble bath' produced 'white' bubbles instead of blue ones?

As I was half asleep I thought it must have something to do with one of the ingredients in 'bubble bath' that causes the 'bubbles' enabling them to be white no matter what colour the initial liquid is. However, upon waking up this morning I realised an ingredient wouldn't make any difference...

:  ": Why r bubbles in baths so white? Surely blue liquid = blue
                                 bubbles? ?.... :D xxx

Not Chemistry but Physics
Why? If you think about it, the 'surf' on a wave is always white isn't it? And when you pour a fizzy drink (be it cola, lemonade or Fanta orange) there's always a white 'fiz'.

So the cause of the 'white bubbles' must have nothing to do with the colour of the liquid, or type of liquid (seeing as I doubt coca cola and bubble bath have the same ingredients?).

So why are they white?
Well what colour lights are in your bathroom? I'm guessing regular white bulbs? (see where I'm going?). At first I thought it has to have something to do with chemistry, but it's actually physics at work here.

A Prism - How white light can be split into different colours
(Taken from Pink Floyd's Album cover: Dark side of the moon)

White Bubbles:
What is a bubble? Well it's a spherical shaped thin layer of 'translucent' liquid, with essentially an 'empty' centre (I don't mean 'space empty' i just mean 'no liquid in the middle empty'). The outside of this 'bubble' is full of bright light from your bathroom (otherwise known as 'white' light). The inside of this bubble is somewhat darker as there's no light souce inside the bubble. So what happens is some of the 'white light' from the room 'reflects' off the outer surface of the bubble (like a mirror) and what our eyes see is 'white'. This therefore gives us a 'white bubble'.

White bubbles in your bath (taken from Clipart)

Still want colour bubbles?
So there you go, you now know the answer to the question: 'Why do we have white bubbles?' However, if you really want blue/green/red bubbles - you can!
Just change that bathroom light bulb to a red/blue or green one and then you can enjoy your colourful bubbles! ;-)

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