You will need:
- Kitchen roll
- Felt tip pens
- Water
- Bowl or cup
- Scissors
What to do:
- Cut a long strip from one sheet of kitchen roll. It should be 2 cm or 1 inch wide.
- Choose one felt tip pen and draw a big dot at the bottom of your kitchen roll strip. IMPORTANT: Do not draw the dot all the way at the bottom, leave about 2 to 3 cm from the bottom to the dot.
- Pour some water into a bowl or cup.
- Place the bottom of your kitchen roll strip in the water and watch what happens. IMPORTANT: When you do this, the dot must be above the water.
- Repeat the method with other felt tip pens.
Background
The inks in felt tip pens are made by mixing different colouring materials, called “pigments”. We can use chromatography separate the different colours because some are soaked up the kitchen roll faster than others.
The reason is that the different pigments have different solubilities in water. The further the colour travels, the more soluble it is. Less soluble colours stay at the bottom.
You can watch a video of this experiment here:
A tang of science 