Who wrote the ransom note?
Ink is a complex chemical made up of different colours which can be separated because they are carried at different speeds by water (if the ink is water soluble). Detectives can work out whether a specific pen has been used in a crime by examining the ink and the patterns it creates when it separates.
3 different black pens (water soluble)
One coffee filter paper, cut into wedges
Glass with <1cm water
Ransom note written with one of the pens – don’t show anyone which pen you used
Willing volunteers to be detectives.
- Cut the filter paper into wedges
- Show the volunteers as you draw a dot of each black pen on the filter paper, 2cm from the bottom of the wedge. Mark these A, B&C in permanent pen. See picture below.
- Dip the thin end of each wedge into a glass of water. The water will immediately be absorbed by the paper
- As the water reaches the ink dots, they will start dissolving into the paper – what colours can you see appearing?
They should all be making different rainbow patterns up the wedge.
These patterns can then be compared to the pattern left by the suspect’s pen.
If a permanent marker was used, a solvent other than water would have to be used to dissolve the ink.