Black ink contains pigments of many different colors. Acting together, these pigments absorb all the frequencies of visible light. Because no light is reflected, the ink appears black. We can use molecular attractions to separate the components of black ink through a technique that is called paper chromatography. What you need: black felt-tip pen or black water-soluble marker; piece of porous paper, such as paper towel, table napkin, or coffee filter; solvent, such as water, acetone (fingernail-polish remover), rubbing alcohol, or white vinegar Procedure:
1. Place a concentrated dot of ink at the center of the piece of porous paper.
2. Carefully place one drop of solvent on top of the dot, and watch the ink spread radially with the solvent. Because the different components of the ink have different affinities for the solvent (based on the attractions between component molecules and solvent molecules), they travel with the solvent at different rates.
3. Just after the drop of solvent is completely absorbed, add a second drop at the same location as the first one, then a third, and so on until the ink components have separated to your satisfaction. Paper chromatography was originally developed to separate plant pigments from one another. The separated pigments had different colors, which is how this technique got its name—chroma is Latin for “color.” Mixtures need not be colored, however, to be separable by chromatography. All that’s required is that the components have distinguishable affinities for the moving solvent and the stationary medium, such as paper, through which the solvent will pass.