The secret of colours

Can I hide a secret message using colours?

White light, like sunlight is made up of all the colours of the rainbow and we see it as white light. An object like a white wall reflects all of these colours and we see the object as white.

When we see a coloured object like a red ball, we only see the ball as red because only the red light is reflected off the ball to our eyes, all the other colours of the rainbow are absorbed.

If you look at an object through something like a sheet of red plastic film or glass, then everything looks red!

We call this a filter. It only lets through red light, so that’s the only colour that gets to your eyes. We say it only transmits red light. So now my eyes see everything as some shade of red.

If you look at the red ball through the red filter, the red can get through and it looks red.

But if I use a blue filter, the ball only reflects red light, and the blue filter only lets through blue light, so almost no light reflecting off the ball gets through and the ball looks black.

We can use this to make some secret messages. You just need some white paper, coloured pencils, textas, or crayons, and some red coloured plastic to use as a filter.

Write your secret message in blue, green and purple. Then using red, yellow, orange and pink draw loads of other letters in a jumble all around it so it is hard to make out any words.

Then look at your picture, the letters in your secret message will appear black and stand out more, while the other letters and the white paper will appear as red, so you can't see them. It makes the secret message easy to read. You can also do this with a blue filter just by swapping the colours around.

How illuminating!