As I pour into each smaller vessel there are cries of amazement and "How did you do that?" as each turns a different colour.
Adding two half-filled vessels to make full ones changes the colour again and again and the children excitedly guess which colour I am going to "magic" next while they answer my questions about capacity.
With a little help they soon relate it to their colour-mixing sessions in art and guesses became more accurate.
I explain how I have created the "magic" but it has given them a lesson they have not forgotten and they even remember the maths.
Year 1 class teacher and PSHE co-ordinator, Craven Park School, London borough of Hackney