Some materials appear homogenous, but are actually a combination of substances.
For example, green plants contain a mixture of different pigments. In addition, the black ink in the pens that are used in this experiment is a mixture of different colored materials. In many instances, we can separate these materials by dissolving them in an appropriate liquid and allowing them to move through an absorbent matrix, like paper. Paper chromatography is used in this experiment to separate the components of black ink. As the solvent is pulled by capillary action up the absorbent paper, it passes through the words written in ink on the paper.