As far as easy science activities go, this is a reliable standard that I think has earned its place as a go-to project for times when something quick and super easy is called for. The basic idea here is exploring the science of chromatography through the use of everyday household materials and really, it couldn't be simpler. Essentially, chromatography is the process of separating chemical mixtures into their individual parts along a stationary piece of material so that it is possible to observe the different components of the mixture. Ink works especially well for basic chromatography because as much as a given color of ink appears to be one uniform color (red looks, well, red), inks are actually mixtures made up of many different colors together, and it is possible to separate out the individual colors.
A sheet of paper towel or some plain coffee filters
Felt tip pens in a variety of colors (make sure to include at least one black pen)
Clear glass jars
What you will do:
Begin by cutting the paper towel into strips. We used strips about 1 1/2 inches wide by 5 or 6 inches tall. Choose a handful of ink colors you'd like to try out. This activity is generally done with different black inks (because they really are the most fun in many ways) but my daughter was more interested in colors, so we chose a wider variety of pens to use. Anything will work, really.
Using a different color of ink for each strip of paper towel, make a mark on each one that is about the size of a dime.
Place each strip into a clear glass jar or drinking glass, and add about a half inch of water to the bottom of the jar. Make sure that the water doesn't touch the ink dot directly and that it sits below the dot in the jar.
The water will begin to wick up the strips of paper towel, and you'll see that the ink begins to "move." As the water rises up the paper towel pieces and they get wet, the ink will begin to move upward with the water. What's interesting here is that the uniform ink mixture will begin to break apart. Darker colors, which are heavier, will stay at the bottom of the paper and the brighter (also lighter) colors will move up.
Leave the pieces of paper towel in the jars until the water has wicked all the way up and the strips are completely damp.
Set the strips aside to dry, and then take a few minutes to observe them. What colors were the inks made up of? Did some inks separate better than others?
What's at work:
I touched on it a bit already, but the basic idea is this: most ink is actually a mixture of different inks and can be separated into its individual components. When it is exposed to the paper towel and given the help of the wicking action of the water, the ink mixture begins to separate and the individual inks that make it up behave according to their individual properties. Heavier colors (the darker ones) will stay near the bottom of the paper, lighter ones (the lighter colors) will rise to the top.