What is happening?

The science behind paper chromatography

How did a simple black marker help solve Mackey's Lunchbox Mystery?

The answer is paper chromatography. Scientists use this technique to separate mixtures into their different parts. In this chromatography experiment, the black ink wasn't made from just one colour. Instead, it was a mixture of many different pigments that were hidden inside the marker all along.

When the pigments separated, they created a unique pattern that acted like an ink fingerprint

.

Why isn't black ink really black?

Although black ink looks like a single colour, it is usually made by mixing several different coloured pigments together.

Different brands of black markers often use different combinations of blue, purple, green, brown or yellow pigments. That's why two black markers can look identical on paper but produce completely different patterns during a paper chromatography experiment.

These hidden colour patterns are called chromatograms, and scientists can compare them just like fingerprints.

Why do the colours separate?

When the bottom of the coffee filter touches the water, the water begins travelling upwards through the paper. This movement is called capillary action.

As the water moves, it carries the ink pigments with it. Some pigments dissolve in the water more easily and travel further. Others stick more strongly to the paper fibres and move more slowly.

Because each pigment behaves differently, the colours gradually spread apart into separate bands, revealing the hidden colours that made up the black ink.

How do forensic scientists use chromatography?

Chromatography isn't just a classroom experiment—it is an important tool used in forensic science.

Scientists can compare inks from anonymous notes, questioned documents or altered records to see whether they were written using the same pen or marker. Chromatography is also used to identify dyes in foods, medicines, plants and environmental samples.

Although chromatography alone cannot prove who wrote a note, it provides valuable scientific evidence that can be combined with other clues during an investigation.