Permanent Rainbow

When rainbows appear after a rainstorm, their ephemeral beauty soon fades as the moisture dissipates. But you can create your own lasting rainbow with a few household supplies!

What You Need

• Clear nail polish
• A tin foil pan
• Black construction paper
• Water
• Paper Towels

What to Do

1. Place black construction paper at the bottom of the tin foil pan.

2. Fill tin foil pan with water about halfway full.

3. Make sure the black construction paper stays at the bottom of the pan. Holding it in place for a few seconds should do the job.

4. Open the nail polish and allow one single drop to fall onto the water in the pan.

5. Wait 10-30 seconds and watch the nail polish expand to cover the top of the water.

6. Lay out paper towels to place the construction paper on.

7. Allow the polish to dry for 5 minutes, the edges of the shape will crinkle a little as the polish dries, then reach down around the polish to the bottom of the pan and pick up the black construction paper by a corner.

8. Pull it up slowly allowing the construction paper to touch the finger nail polish.

9. When the construction paper touches the polish it will stick to the surface.

10. Allow the construction paper to dry on the paper towels.

What's Going On?

The visible spectrum has wavelengths ranging from about 400 nanometers (nm) to 700 nm. Light travels differently through the nail polish than it does through air, and when the nail polish dries, it does not have a uniform distribution of thickness.

The light slows down when it reaches the polish, travels through at a slower speed, reflects off the bottom, and travels back out. As the light travels through the polish, the light waves interfere with each other. Constructive or destructive interference patterns will emerge, resulting in different output wavelengths and, consequently, different colors.

Each color of light in the visible spectrum has its own frequency. So for instance, if a blue color is visible it means other colors in the visible spectrum interfered destructively and blue interfered constructively. The colors that appear from the nail polish are different colors because the light travels varying distances through the film. The center of the film will be the thickest, and the film gets thinner farther away from the middle. For a color to appear multiple times, it must be integer multiples of half of the wavelength.

Apply It!

Where do the multiple colors come from? How do you think constructive and destructive waves play a part in the colors that are displayed? If a light is made up of red, green and blue, and the red and green waves destructively interfere, which color will be displayed?

- Jamie Garrett