Walking Water Rainbow

What you need

• Clear cups, 6
• Water, enough to fill 3 cups
• Food coloring, red, yellow and blue
• Plate or tray, 1 tray to catch drips (optional)
• Paper towels, 6 sheets
• Pitcher, 1, or a large cup
• Towel, 1 cloth for spills

How to do it

Grown-up prep: Clear a table spot away from the edge and lay down a tray or old towel, since food coloring can stain skin, clothes and surfaces. Fold paper towels into long strips, about two fingers wide. Keep a cloth handy for spills so the floor doesn't get slippery.

1. Line up six cups in a ring on the tray.
2. Fill every other cup most of the way with water.
3. Add red, yellow and blue drops, one color per full cup. Stir gently.
4. Fold each paper towel strip in half lengthwise to make a skinny bridge.
5. Drape one strip between each pair of neighboring cups, one end in each.
6. Guess what color will appear in each empty cup. Say it or draw it.
   Ask: What color do you think red and yellow will make together? What about yellow and blue?
7. Wait about an hour. Peek every 15 minutes to watch the colors climb.
8. Check the empty cups. Compare what you see with your guesses.
   Ask: Which guess was right? Did any color surprise you?
9. Toss the soggy strips, pour the colored water down the sink, and wipe drips.
10. Now show your friends, or build another ring! What new colors could you make?
    Ask: Who could you invite to guess the colors before they appear?

Play it again

• Color swap: put the colors in a different order around the ring and guess the new mixes first.
• Bridge race: try wide and skinny paper bridges and see which one walks the water faster.
• Two color trick: make only two full cups, like red and blue, and predict the one new color.