Separating Colors: Investigating Inks and Dyes

Needed:

  • White blotting paper (or large coffee filters)
  • a dish or saucer of water
  • inks or dyes (such as food coloring, felt pens)
Experiment:
  1. Cut the blotting paper or filter paper into long strips about 1 inch by 1 foot (2.5 cm x 30 cm).
  2. Put a drop of the ink or dye you want to test about 1 1/2 inches (3.5 cm) from one end of the paper.
  3. Hang the paper strip up so that the end with the drop of ink or dye on it dips 1/2 inch (1.3 cm) into the saucer of water. You will soon see colored bands spreading up the paper.
  4. Take each strip of paper out of the water when the color is near the top. Let the paper dry and examine the colors closely.
Explanation:
The paper soaks up water from the saucer and the water carries the different colors up the paper. The different colored pigments travel at different speeds up the paper so you will be able to see separate bands of color. This is called chromatography. Some inks and dyes contain only one color but others are mixtures of two or more colors. Water moves up the paper because of its ability to climb along the tiny tubes and holes between the paper fibers. This movement is called capillary action, and it explains how sponges soak up water, how trees get water up to their leaves, and how you just separated ink samples!

Colored objects are able to reflect some of the colors in the light that falls on them because they contain substances called pigments. You can find out more about pigments by investigating the inks and dyes that people use to color things. Many substances contain several different pigments, which each reflect a different color of light. When you mix paints you are mixing pigments.