Chromatography: Be a Color Detective

1. Cut the coffee filters into strips that are each about one inch wide and at least four inches long. Cut at least two strips, one to test brown and one to test yellow. Cut an extra strip for each additional color you would like to test.
2. Draw a pencil line across the width of each paper strip, about one centimeter from the bottom end.
3. Take the brown marker and a paper strip and draw a short (about 1 cm) line on the middle of the pencil line. Your marker line should not touch the sides of your strip
4. Use a pencil to write the color of the marker you just used on the top end of the strip. Note – do not use the colored marker or pen to write on the strips, as the color or ink will run during the test.
5. Repeat the previous two steps with a yellow marker and all the additional colors you would like to test.
6. Hold a paper strip next to one of the tall glasses (on the outside of it), aligning the top of the strip with the rim of the glass, then slowly add water to the glass until the water level just reaches the bottom end of the paper strip. Repeat with the second glass.

1. Fasten the top of a strip (the side farthest from the marker line) to the pencil with a binder clip or clothespin. Pause for a moment. Do you expect this color to be the result of a mixture of colors or the result of one color molecule?
2. Hang the strip in one of the glasses that is partially filled with water by letting the pencil rest on the glass rim. The bottom end of the strip should just touch the water level. If needed, add water to the glass until it is just touching the paper. Note - it is important that the water level stays below the marker line on the strip.
3. Leave the first strip in its glass as you repeat the previous two steps with the second strip and the second glass.
4. Watch as the water rises up the strips. What happens to the colored lines on the strips? Does the color run up as well? Do you see any color separation?
5. When the water level is about one centimeter from the top (this may take up to 10 minutes), remove the pencils with the strips attached from the glasses. If you let the strips run too long, the water can reach the top of the strips and distort your results.
6. Write down your observations. Did the colors run? Did they separate in different colors? Which colors can you detect? Which colors are on the top (meaning they ran quickly) and which are on the bottom (meaning they ran more slowly)?
7. Hang your strips to dry in the empty glasses or on a drying rack. Note that some colors might keep running after you remove the strips from the water. You might need longer strips to see the full spectrum of these colors. The notes you took in the previous step will help you remember what you could see in case the colors run off the paper strip.
8. If you have more prepared strips, put them in as you did with the first two strips, and run them until they are completed, similar to the first strip. What do you observe this time? Do these colors run in a similar way as your first set?
9. Repeat the procedure, if needed, until all the strips are done.
10. Let all the strips completely dry.
11. Look at your strips. How many color components does each marker color have? Can you identify which colors are the result of a mixture of color components and which ones are the result of one color molecule? Are individual color components brightly colored or dull in color? How many different colors can you detect in total?

Extra: Most watercolor marker inks are colored with synthetic color molecules. Artists often like to work with natural dyes. It is fairly easy to make your own dye from colorful plants or spices like blueberries, red beets or turmeric. To make your own dye, finely chop the plant material, place it in a sauce pan and add just enough water to cover the plant material. Let the mixture simmer covered on the stove for approximately 10 to 15 minutes. If, at this point, the color of your liquid is too faint, you may want to remove the lid of the saucepan and continue boiling until some liquid has evaporated and a more concentrated color is obtained. Let it cool and strain when needed. Now you have natural dye. To investigate the color components of this dye, repeat the previous procedure, but replace the marker line with a drop of natural dye. A dropper will help create a nice drop. Let the drop of dye dry before running the paper strip.  Would the color of your natural dye be the result of a mixture of color molecules or would it be the result of one specific color molecule? Does the marker of the same color as your natural dye run in a similar way as your natural dye?

Extra: In this activity, you use water-soluble markers in combination with water as a solvent. You can test permanent markers using isopropyl rubbing alcohol as a solvent. Do you think similar combinations of color molecules are used to color similar-colored permanent markers?

Extra: You can investigate other art supplies like paints, pastels or inks in a similar way. Be sure to always choose a solvent that dissolves the material that is being tested to run the chromatography test. Isopropyl rubbing alcohol, vegetable oil and salt water are some examples of solvents used to perform paper chromatography tests.