Fountain pen and ink jar.

Catching criminals with colour

Follow these instructions to create your own chromatography activity and learn about how ink can help forensic scientists to catch criminals.

• 26 June 2006 | Updated 14 October 2011

• What you need
• What to do

A ransom note has been written. Forensic scientists extract the ink from the envelope so that it can be analysed. The extracted ink can then be compared with ink from the pens of the suspects.

What you need

To do this activity you will need the following items:

• paper towel
• scissors
• a jar
• felt-tipped pens and markers
• two paper clips
• water.

What to do

This is what your experiment should look like.

1. Cut some absorbent paper (such as paper towel) into strips about 2 cm wide. The length isn't really important and will depend on the size of the jar you hang them in.
2. Draw a small circle 1 cm from the bottom of the paper with different black markers or felt-tipped pens.
3. Fill a clean jar with about 1 cm of water and carefully place the paper into the jar making sure that the bottom of the paper is in the water. The circle must be ABOVE the water level. Use paper clips to hold the paper upright in the jar. Watch the water rise up the paper.
4. After a few minutes remove the paper from the jar. Notice how different colours in the ink travel up the paper at different speeds.
5. Now try some different colour pens and markers. Can you see any differences?
6. Did you have any pens for which the ink did not separate? If so, repeat the experiment using methylated spirits instead of water in the jar. Try out a variety of pens. Can you see any differences?  

The method used to compare inks is called chromatography. It involves separating the ink in each of the pens. As the solvent (water) rises up the paper, the different colours of the ink separate.

Ask your family to play your suspects. Have them use specific pens for the job and see if you can figure out which ink comes from which pen and nab your suspect!

Itching for more forensic fun? Check out our fantastic Forensics kit at the CSIRO Education Shop.