Equipment: filter paper/a circle of craft paper, felt tips, glass of water, pipe cleaners.
How to: using a felt tip, draw a single-line circle around the middle of the filter paper; only use one colour; fold the circle into a cone shape; place the cone in the glass so that it is just touching the water; what happens as the paper absorbs the water? After a couple of hours, lie the paper out to dry, then use a pipe cleaner to scrunch the middle together and create a butterfly shape.
What is happening? Chromatography is a technique for separating mixtures. Here, the ink of the felt-tip (the sample) is put on the paper (the stationary phase) and the water then moves up the paper (the mobile phase). The different pigments of the ink have different properties (more/less soluble etc) which means they travel at different speeds and separate.
Taking it further: children could explore different felt tip colours, different sizes of circles or different sizes and types of paper. They could also use rulers to measure the distance travelled by the different colours.