Why are bubbles colourful?

For this activity you’ll need some water, dish-washing liquid, a black container such as a cup or a jar lid painted black on the inside, a shallow dish, a piece of white paper and a spot near a window or under a bright light.

1. Grab a small bowl and add 1 part dishwashing liquid in 10 parts water. Add more dishwashing liquid if you are having trouble making bubbles or let the mix rest over night.
2. Place the white paper in a brightly lit place such as next to a window or under a bright light.
3. Pour the mix into a shallow dish, dip the open mouth of the lid or cup straight down into the soap solution. When you pull it out, a soap film should have formed over the opening. If you are having trouble, try dipping your hand into the bubble mix and swiping it across the edges.
4. Turn the lid or cup onto its side and hold it over the piece of paper. Can you see stripes of different colors forming?

Bubbles are made up of water with a thin layer of soap on either side. White light contains all the colours of light combined. When that light shines on a bubble it bounces around those layers and some of it reflects back to our eyes. The colours that you get depend on the thickness of the water. With a spherical bubble we see those colours swirling as the water moves around the bubble, changing as the water evaporates and wind spins them about. When we make our flat bubble we can see the colours organised by the thickness of the water as gravity pulls the water towards the ground.

Our Scienceworks challenge to you

Take a bubble wand and blow a bubble. Take note of the colours swirling and changing. Now let the bubble land on a smooth surface like a plastic lid with a little bubble mix on it. Do the colours keep swirling or do they form rings? Does your bubble always pop or can you see it start to go invisible at the top? Can you still pop the bubble if it goes invisible?