The Colors Behind a Black Dot

A black marker can hide a team of colors. Its ink may contain several dyes, which are substances that add color. Paper chromatography is a way to separate those dyes so you can see them. The process uses moving water and absorbent paper, which soaks up liquid. Follow the stages below to turn a dark dot into a trail of clues about the ink. The headings name each stage of the investigation.

Gather the Tools. For this investigation, collect a white paper coffee filter, a clear cup, water, a pencil, tape, scissors, and a washable black marker labeled water-soluble. That label means its ink can dissolve in water. Do not choose a permanent marker; its ink may not dissolve well in this experiment. Cover your work surface before starting.

Prepare the Paper. Cut a strip from the coffee filter. Make it narrower than the cup and long enough to reach from the rim to the bottom. Draw a light pencil line across the strip about one inch above its lower end. Put a small black marker dot at the center of that line. Let the dot dry. The pencil line marks the starting place without adding ink dyes.

Start the Water. Add about a quarter inch of water to the cup. Tape the top of the strip to a pencil and lay the pencil across the rim. Adjust the strip so its bottom touches the water but the ink dot stays above it. If the dot sits underwater, ink may spread into the cup instead of traveling up the paper. Solve that problem by pouring out a little water.

Watch the Climb. Leave the cup still. Water creeps upward through tiny spaces in the paper. This movement is called capillary action. As the water reaches the dot, it dissolves dyes and carries them along. Some dyes travel more easily with the water, while others cling more strongly to the paper. These differences can produce separate colored bands. The colors depend on the ink, so your result may surprise you.

Save the Evidence. Before the water reaches the top, remove the strip and lay it flat to dry. Draw the dried strip and label the colors you observe. Beneath your drawing, write a caption, such as “Colors after paper chromatography.” This record lets you study the result after the experiment ends.

Read the Result. Several bands are evidence that the ink contains a mixture of dyes. One band does not prove that there is just one dye. Some dyes may stay together or may not dissolve well. By following the steps in order, you make hidden ingredients easier to investigate.