Color magic

What you’ll need

  • Filter paper, e.g., coffee filters
  • Small white napkins or paper tissues
  • Various dark-colored felt-tipped pens, e.g., black, blue, dark green, purple
  • Scissors
  • Adhesive tape
  • Two (jam) jars
  • 100 ml water
  • 100 ml alcohol (e.g., 70% medicinal or rubbing alcohol)
  • Optional: fine and coarse salt

How to do it

1. Cut out two rectangles from the filter paper (approx. 10 × 6 cm).

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2. Roll the paper into a cylinder and fasten with a small piece of adhesive tape.

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3. Take a felt-tipped pen and make a large dot in the middle of two paper tissues. If you like, draw other dots around it using other felt-tipped pens.

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4. Place a paper tissue over a pen. Place the colored tip in the middle of the tissue at precisely one end of the pen and carefully press the tissue into the rolled-up piece of filter paper. Then pull out the pen. Do the same with the second tissue and the second roll of filter paper.

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5. Fill one jar with water and one jar with alcohol so that the liquid is about 1 cm deep in each jar. Now, place the rolls of filter paper upside down in the jars so that the tissues stick out at the top.

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6. Now, you’ll have to wait until the rolls of paper have fully absorbed the liquid and the colors have run almost to the edge of the napkin (but not quite). This can take 10 to 20 minutes, depending on the paper.

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7. Remove the rolls of filter paper containing the tissues from the liquid; pull out the tissues very carefully and allow them to dry. To get pattern effects in the ink, you can also sprinkle salt over the wet tissues.

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Well spotted!

The liquid has moved through the filter paper and turned the colored dots into a multicolored circle. There are new colors in addition to the originals.

What's the secret?

The ink in a dark felt-tipped pen is a mixture of different colors. When the liquid comes into contact with the ink on the tissue, it breaks down the ink in the felt-tipped pen back into its original mix of colors. The different inks in the felt-tipped pens break down to different degrees and therefore are not all transported equally far. In particular, there are big differences between water-soluble felt-tipped pens and those that are only soluble in alcohol.

Try the experiment with just one color and you’ll see that dark felt-tipped pens are made up of a surprising number of different colors!

If the wet ink is also sprinkled with salt, the salt crystals absorb some of the humidity faster than it evaporates. Therefore as the ink dries, it tends to move towards the salt crystals and to gather around them, resulting in a granular texture.