Mixing primary colours and using up old food colouring

Over the years, I've accumulated more little bottles of food colouring than is maybe sensible.  And I've been dubious about using the decade-old ones for cakes for little people (so we acquired new purple, orange and green for a Gruffalo, and red and black for a big red bus, and goodness knows what I'll be buying and making this year...).  Anyway, I've got an array of little bottles of colours without a good use for them until now.

Gruffalo cake
Gratuitous photo of the Gruffalo cake.  Also for anyone else attempting a Gruffalo, the rest of the blog describes why you don't need to buy orange, green or purple food colouring if you already have red, blue and yellow!

I've mentioned that we've got the Primary Science Lab Set from Learning Resources in my last blog.  One of the idea cards it contains suggests mixing primary colour food colouring.  We deviated a little from the instructions to have a tube of each colour, and to mix them in the conical flask.  We put some water in the beaker and practiced tipping it carefully through the funnel into the conical flask before each "experiment". We then put some of either red, yellow or blue (a couple of drops of food colouring in about 100ml of water) in the flask with the pipette before adding another colour to see what colour it made when mixed. It worked nicely with a piece of white paper underneath.

The lab set is aimed at 4-8 year olds, and my not-quite-3 year old is probably more into playing with water and perfecting his pouring skills than the older end of that age group would be, so their method is a quicker demo of what happens when the colours mix.

We mixed red and yellow to make orange, red and blue to make purple and blue and yellow to make green.

We have done this a few times now and it's a hit - I've been asked to "play colour science" a few times now and on several occasions we've made each colour more than once. He's now got the hang of telling me which colours we need to mix together, but he's a stickler for process and we have to pipette each thing laboriously into the flask rather than pouring! We've also had the table swimming in coloured water a few times when clumsy little hands have knocked things over...

Pipetting food colouring
Squirting coloured liquids around whilst wearing a lab coat is brilliant fun!

As with the red cabbage indicator "experiment", you don't need any fancy kit for this, a few yoghurt pots and some food colouring would work just fine, but the fun seems to be as much in moving different liquids around as seeing what happens when the colours mix for a not-quite-3 year old.