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
- 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
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.