"Is green really green?
You will need:
strip of paper towel
green felt-tipped pen or 1 drop of green food coloring
jar or glass with 1 inch of water
What to do: Make a spot of color about 2 inches from one end of the strip of paper towel. Hang the strip in the jar so the spot is above the water and the end of the strip is in the water. Let it stand for 15 to 20 minutes.
What happens: The green spot is gone but above the original spot, the paper has turned blue, and above that the paper is yellow.
Why: Most dyes and inks are combinations of coloring substances which can be taken apart by adding water or alcohol. Water moves up the paper the same way as sap rises in trees. As the water moves up, it dissolves the green spot and gradually moves the color up the strip of paper. But since the colors that make up green - blue and yellow - do not move at the same rate, they separate."
What happened when CKS tried it? I tried ink and food coloring. The food coloring was opposite from the ink because the blue is at the top, the green is in the middle, and only a little yellow at the bottom. And on the ink, there is a lot of yellow on the top and there is a little green in the middle, and some blue on the bottom. Ink worked better. Advice from CKS for when you try this at home: don't forget to label your paper towel strips.
CKS rating: 5 stars - Wow, better than TV!