Secret Messages Using Ink Pen Chromatogrphy

Chromatography is a technique that scientists use to separate things. A good analogy for this is to picture bees and wasps flying in a pack over a flower bed. The bees will be attracted to the flowers, but the wasps will just keep moving. If you were standing just at the end of the flower bed, you would see the wasps fly by first (unattracted to the flowers) and the bees second (their attraction to the flowers slowed them down). [Credit wikipedia] Scientists in a lab will often use similar techniques to separate things. Today we are going to try to separate the inks in pens. Did you know that there is more than one color in your black marker? How many colors do you think there will be? Some colors will stick to the paper more than other colors, thus, just like the wasps and bees, the colors will separate.

Completely Safe.

Filter paper
Black water soluble pen
Black permanent pen
Cup and water set up

Write a secret message in permanent (caps) and washable marker on the filter paper:
SeCret In mEssage. Need CodE.
Or
ChrOmatOgrapHy! (where only the first leg of the H is in permanent ink, so that the secret message is “cool!”)
Codes may be made ahead of time, and you can make your own with your students if there is extra time. You can give the following scenario if you want to:

Imagine you are part of a spy network, and you are trying to leave a code for a friend, but you don’t want anyone else who finds it to read it. One way to make a secret message would be by using three different pens, with different inks. Maybe the inks look the same, but are CHEMICALLY DIFFERENT.

How do you think someone made this code message?
What inks did they use?
How can we tell the inks are chemically different?

The water soluble ink was able to travel with the water up the paper, while the permanent ink stayed behind, revealing the message!

Chromatography was invented in 1910 by Russian botanist Mikhail Tsvet. He used it for separating the pigments that made up plant dyes. This technique provides an easy way to separate the components of a homogeneous mixture. Chromatography uses two phases (states of matter) to separate a homogeneous mixture because each component of the mixture has different affinities to each phase. We have a stationary phase (solid material), and a mobile phase (liquid or a gas). Some components of the mixture will stick to the solid better than others so each component will move at different rates so we can separate them. The rate at which a compound moves depends on the size of the molecule and the solubility in the solvent.

No special clean up; water goes down the drain, paper in the trash.