Easy Chromatography Experiment: Finding Dye Composition in Ink

In this experiment, you can find out what dyes make up different colours of marker ink and why, turning boring old ink into an array of different colours.

Supplies needed:

1. An assortment of different coloured textas and markers
2. Paper towels (or filter paper)
3. A glass of water or a container

Cut the paper towel into strips, around 30mm (1.4in) wide. Then, using one of the markers, draw a horizontal line across the paper towel, leaving about 10mm of clearance from the bottom. The colours that generally produce better gradients are the complementary colours (orange, green, purple), black, and brown.

Fill the glass one-third full with water and slowly dip the paper towel in, being careful to not put the line underwater. Then, tape the top of the strip to a wall, being careful to move the glass or container away from the wall, making sure the paper towel strip does not touch the wall which could inadvertently dye your wall (although if you did it would look nice).

Watch as the water slowly creeps up to the line, and then spreads the colours upwards. At first, it may look boring, but after a few minutes, you should be able to see a nice gradient of colour, showing the different dyes within the ink. Now try again with another!

So why does this happen?

Chromatography occurs because marker ink isn't usually one colour, but a mixture of different coloured dyes, all combined to create the colour you see. For example, a black marker may look uniform at a glance, but it can actually contain red, yellow, and blue dyes. When you dip the strip in water, the dyes separate due to their different solubilities.

Solubility is the tendency of a solute (like dye) to dissolve into a solvent (like water). If the dye is more soluble in water, it travels further, like a surfer riding a wave to the shore. If the dye is less soluble in water and sticks more to the cellulose fibre, it travels minimally or very little, like a rock in the middle of the ocean.

As a result, the original solid line separates into several coloured bands that if you were to mix together, would create the same ink that you started with.

This simple trick is the actually the same technique that forensic scientists use. By seeing the composition of dyes, and as no brand of marker is the same, they can trace the "fingerprint" back to the pen. Theoretically tracing a ransom note back to a suspect. This can also be used in finding fraudulent documents by checking if there is more than one ink used, which can indicate that it was altered.

And that's the end to this Instructable — a simple way to almost magically separate and see the different dyes inside everyday markers, which has actual uses in the real world. If you complete this project, I'd love to see your coolest chromatography pattern, so please share below. Thanks for reading!