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Double rainbow on St Clements

Hello again,

I hope everyone is keeping well.  This week I thought we'd have a range of activities on a rainbow theme.  Don't forget to let me know whether you had a go at any of these activities.

Create a rainbow

First, have a go at creating a rainbow.  This probably works best if bright sunshine is coming in from a window.  You may already have stuff in the house which creates rainbows eg crystals, edges of mirrors etc.  If not, have a go at creating one with a mirror in a tray of water as shown on this web page


Another place you can see rainbow colours is in bubbles, so now is the time to get out your bubble mix.  If you haven't got any bubble mix, then try this recipe .

My bubble making friends have the following tips on creating the above bubble mix:

  • Make sure you use baking powder NOT bicarbonate of soda (they are not the same thing)
  • The cornflour will be very difficult to dissolve but don't be tempted to use a blender as then it won't work
  • In the UK, fairy liquid is probably the best washing up liquid to use (although I've heard good things about Ecover)

If you can't get all the ingredients for the recipe together carefully mixed washing up liquid and water on its own (or with glycerin) works pretty well for smaller bubbles. 

My top tip is leave the mixture to rest over night - it will work much, much better if you do.

Once you have your bubble mix, go outside and blow some bubbles.  If you look carefully you will see the bubbles have lots of swirling rainbow colours which change over time. As more of the liquid in the bubble runs to the bottom black spots form near the top and join together just before the bubble bursts.  It's something Isaac Newton found particularly interesting. 

CD Spectroscope

You can also get rainbow effects using angled CDs or DVDs in sunlight (or a bright lamp). You can use this fact to build a spectroscope.  These are used by astronomers to work out what stars are made of and by jewellers to assess precious stones.  Arvind Gupta has a design that is a bit fiddly to make but works really well.  I recommend his toys from trash pages generally for some great ideas of things to do.  If you want to know a bit more about the science take a look at these resources from Oxford Sparks (the two spectroscope resources for KS3 and KS5 use the Arvind Gupta template). 

When you use the spectroscope NEVER use it to look directly at the sun.


Although most rainbows are created with light, you might like to have a go at some chromatography where you split the ink from coloured felt tip pens into different colours.   There's a bit more information about it on this page. My main tips are:

  • Use salty water (it makes the inks spread out better)
  • Use water soluble pens (crayola washable are good if you have them)
  • Avoid yellow, cyan or magenta coloured pens as they are most likely to be pure dyes (see if you can find out why)
  • Assuming you don't have chromatography paper try coffee filter paper or kitchen towel

Rainbow E-cards from Quentin Blake

Finally, take a look at these lovely, free e-cards from Quentin Blake on the theme of rainbows.  Why not send one to a friend or relative that you aren't able to visit.

That's all from me this week folks.  Do feel free to ask me to suggest activities on a particular theme - I'd love to help you out.