Have you ever wanted to be a detective or a spy? Try this
experiment and see if you've got what it takes!
What you need:
- Different types of felt tip pens
- Jam jar
- Paper clips
- Friends and family
- Kitchen towel or other absorbent paper
- Something that your friends and family can steal - how about
1. Give your friends and family a pen and a piece of kitchen
2. Tell your friends and family that you're leaving your phone
somewhere in the house (don't leave it anywhere where strangers
could take it). Ask your friends and family to decide which one of
them will steal it. The thief has to take your phone and leave a
ransom note on the kitchen towel with the pen that you gave them.
Make sure you don't know who has taken the phone!
3. Return to the crime scene a few hours later. Is your phone
gone? Is there a ransom note? If there is, you can investigate the
4. Gather all the pens as evidence. Make sure you know which
person had each pen. You're going to compare ink from the pens to
the ink in the ransom note.
5. Cut the ransom note into 3cm strips.
6. Cut 3cm strips from a fresh piece of paper towel. With the
first pen, draw a small circle on a clean strip of paper. Repeat
with a new strip of paper for each pen you have.
7. Fill a jam jar with water. Use paper clips to attach some of
the paper strips from the ransom note to the edge of the jar. Dip
the bottom of the paper strip in the water, but make sure the water
doesn't touch the ink.
8. Use more paper clips to attach the strips of paper with felt
tip pen circles to the edge of the jar. Dip the bottom of the
papers in the jar, but make sure the water doesn't touch the ink
9. Over the next hour, the water will rise up the paper. What
can you see?
The ink from each type of pen will separate into patterns of
different colours. Do any of the colour patterns match? Compare the
ink pattern from the ransom note to the pattern of each pen. That's
What's going on?
Felt tip ink is made up of different types of molecules. Each
different pen is made up of different combinations of molecules.
When you dip the paper into the water, the water travels up the
The water dissolves the ink spots. Ink molecules travel with the
water as it continues up the paper. The most water-soluble ink
molecules are carried towards the top of the paper. Less
water-soluble ink molecules don't travel as far. This forms the ink
patterns you can see.
This technique is called chromatography. Real
forensic scientists use it to solve crimes.
You can match the ink pattern from the ransom note to one of the
pens. The person with that pen is the thief!