From the page: The shiny disc asks for a new shine
Idea 8
Rainbow experiment
Diffraction is the phenomenon in which light unfolds when it meets microscopic grooves, and CDs are ready-made diffraction tools: their recorded surface has ultra-fine tracks spaced little more than a micrometer apart. When white light hits these grooves, each color reflects at a slightly different angle — the same principle as retroreflective "cat's eyes," now revealing the visible spectrum in your hand.
What you need
- 1 or 2 old CDs (data or music; the shinier the face, the better)
- Strong phone flashlight or a plug-in flashlight
- Pencil, pen or barbecue skewer
- Hot glue or strong white glue
- Cardboard or cork stopper (for base and support)
- Plain white paper (to project the spectrum)
- Scissors or craft knife
How to make it
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1
Glue the CD (shiny face up) onto a cardboard or cork base, so it sits firm and can tilt without toppling — the stability of the support guarantees a constant reflection angle.
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2
Turn off the room lights: the darker the room, the more vivid the rainbow, because there is no competing light "washing out" the colors.
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3
Point the phone flashlight directly at the recorded surface, holding it about 10 or 15 centimeters away at a low angle — grazing light travels more tracks and separates the colors better.
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4
Rotate the CD slowly and observe the reflected light on a wall or on the white paper: you will see the full spectrum unfold. The paper works as a screen because its matte surface spreads the reflected light evenly.
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5
For a more stable spectrum, glue a small piece of cardboard covering everything but a slit of the flashlight: narrowing the beam sharpens the color bands, like a physics-experiment slit.
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6
Try candlelight, sunlight through the window and LED light: each source has its own "fingerprint" of colors, and you will see differences in the projected spectrum.
Finishing touches
Fix two CDs at a 90-degree angle to project the rainbow onto two walls at once, or cut a CD into slivers (with goggles and care) to create small "prisms" scattered around the room — decor that lights up when light passes nearby.
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