Colourful milk and washing up liquid

A while ago we had a go at what is often referred to as the "magic milk" experiment. The "magic" is really science - it's a result of fat and detergent molecules interacting, with colours carried in the milk moving quickly away from added detergent. Anyway, last time around was a messy disaster with milk and food colouring all over the floor and the baby.

We had another go, as we had some out of date full fat milk and I was feeling brave.  It works better if there's more fat in the milk and I don't like wasting fresh stuff that the smallest one can eat. This time around was far more successful!

I added some food colouring to a children's plate filled with milk, with enough to cover the bottom but only about 5mm depth.  I put the plate of milk and food colouring on the bottom of our cake carrier turned upside down to protect a little against spillages and put some washing up liquid (detergent) in a little pot. I gave the 3 year old some cotton buds (cotton swabs if you're in the US) and asked him to try dipping one in the washing up liquid then putting it on the surface of the milk. He didn't seem to have a recollection of the last time we tried this unsuccessfully (probably for the best...) but he followed the instructions nicely and looked really happy to see a growing circle of white around the cotton bud. 

Coloured milk moving away from the detergent

He repeated it again and again, enjoying creating patterns with the colours. Interestingly the yellow green and blue floated best on the surface, and the initial patterns were mostly green, but after 5 minutes or so, the red which had clumped together in the milk started to float more and little flecks of red whizzed away from the detergent when he touched the surface.  I think it's probably because the red food dye I used is dissolved in water whereas the other colours are in glycerol, rather than being because of the red pigments themselves.

Pattern after several lots of detergent

After 10 minutes, he resorted to "whisking" the milk with the cotton buds to "make pancakes". Once he had an unappealing green mess that started spilling we used the remaining washing up liquid to clean everything up!  Definitely more fun had this time around, and worth repeating.