Cleaning up colourful milk

There are some days when very little goes to plan. And those aren't the days to let a toddler loose with a plate of milk and some food colouring!  However, for some reason, this didn't dawn on me in time, and as a result I spent yesterday afternoon cleaning milk and food colouring off the toddler, his brother, the table, the floor and his favourite toy. They say there's no point crying over spilt milk, so I thought I'd blog about it instead...

I had hoped that another activity involving food colouring and playing with liquids would be of interest to my eldest boy and provide some amusement for the smaller one to watch. This sadly wasn't the case, but on another day it could have been, and when I recover from seeing a plate of coloured milk flying towards the little one I might give it another go!

We had some full cream milk that was close to date (this works best with full cream for reasons I will explain a little later) and I poured this into a plastic plate, with just enough to cover the bottom of the plate. You could use more, but it doesn't improve the effect and is a waste of milk. In a little plastic bowl I mixed some washing-up liquid with water. I also put out a few cotton buds, and some bottles of food colouring. All set, I explained that we were going to put some drops of food colouring into the milk and then dip a cotton bud in detergent, touch the milk and see what happened. My intention had been to explain a little science whilst we repeated it.

What actually happened is that we put some food colouring in, but bizarrely the red we used mostly sank so it was barely visible. The toddler wasn't impressed so leaned across the table to grab the bottle and put more in.  He slipped and put his hand on the edge of the plate, it flipped over and flew towards his brother (who was sitting by the little table watching with interest). The contents of the plate splattered further than might reasonably be expected, including on the elephant toy the big one had put to 'watch' from a supposedly safe distance.

The toddler was quite distressed that he'd accidentally destroyed his experiment and asked me to put more milk on the plate... meanwhile I was trying to clean the previous attempt!  Once his brother had clean clothes and I'd wiped the rest up, we had another go.  It worked, but he wasn't terribly impressed, and before I had a chance to try any explanation of why, he insisted on taking the toy elephant for a bath to get the food colouring and milk off...

Patterns in milk made with blue and red food colouring

The effect that you see when you put a little detergent on the surface is a rapid movement of the colours around the surface of the milk for a short while, creating pretty patterns.  The reason for this is that the detergent molecules interact with the fat molecules which are suspended in the milk.  The greater the fat content of the milk, the more interaction there is; during this process, the food colouring gets moved around because of the moving fat and detergent molecules.  A more complex explanation would involve the polarity and shape of the fat and detergent molecules.  To explain this to the toddler, I was planning to say that the milk, food colouring and the detergent are made up of lots of tiny things called molecules that you can't see with your eye, even smaller than the yeast we talked about last week.  When you mix the milk and detergent, some of the molecules in the milk like to be near to the molecules in the detergent, and they move around to 'make friends'.  As they do this, the food colouring molecules get carried around too.  My hope was to start to introduce the idea of things being made of molecules.  But that will have to wait until another day!