Hidden messages in colour
- White paper
- Coloured pencils, crayons or textas
- Different coloured cellophane such as red, green and blue
- Write a word or message on a piece of paper using a different colour for each letter.
- Place a piece of red cellophane over the drawing.
- Can you still read your message? Which letters disappear? Do any turn a different colour or appear black?
- Try again with a different colour of cellophane. Test what happens when you place two different colours of cellophane over your message. What about three?
- Once you have figured out which colours you can see through your different pieces of cellophane it’s time to start writing a top-secret message or drawing.
- On a new piece of paper write your message in one colour. Scribble around it in different colours to distract anyone viewing your secret message. Give your drawing to someone you want to read your secret message with a piece of cellophane that will show up the message.
What’s going on?
When we see colour it is due to our brain detecting different combinations of light. We see the colour white when all of these colours are mixed together. Colours can vary thanks to reflected light, or light that bounces off something. White paper reflects all colors which is why it looks white to our eyes. Ink from textas or crayon wax reflect only one color.
Red texta ink absorbs blue and green light but allows red to reflect off of your paper and get picked up by your eyes. Like ink, your red cellophane filter also absorbs blue and green light. When you look at your paper through your red filter, the paper looks red because the filter only lets red through. When you drew with your blue or green colors, the ink absorbs the color red. No red light is absorbed by the filter, so you can see those colors through the filter and they’ll almost look the same.
Hold up your cellophane in front of your eyes and look around the room. Try putting two different colours of cellophane together and looking again.