Changing colour

Now try it yourself...

You can write invisible notes to your friends too! Just follow these simple steps:

You will need: lemon, lemon juicer, saucer, paintbrush, white paper, iron, and a book to record results.

Step-by-step instructions:

1. Get a lemon and squeeze the juice out of it into a saucer.

2. Dip a paintbrush into the lemon juice and paint a message onto a white piece of paper. Leave the paper to dry. As it dries the areas you have painted with the lemon juice will become hard to read.

3. Ask a friend or family member to see if they can read what you have painted. Try this out with a few different people and record what they can see.

4. Now it is time to heat the paper and see what happens to the words. Ask an adult to iron over the paper on the opposite side to the one you painted.

5. The heat will make the lemon juice change colour. Show the message to each person now and see if they can read the message.

6. Once the heat has been added and the picture has changed you cannot change it back to being invisible. It is a little like cooking. Once you have cooked something you cannot change it back into being raw again.

Lots of other things change colour when they are heated. Wood on a fire will change from being brown to being hot red and then finally black once the wood is fully burnt. Red meat will turn to brown as it is cooked.

Some things only change colour a little when they are heated. If you boil an egg the egg yolk will get lighter once the egg is hardboiled, changing from the bright yellow egg yolk of a raw egg to a more pastel yellow of a solid egg yolk. The egg white changes from being nearly transparent when raw to opaque white when cooked.

PDF downloads:

• Download this page as a pdf: Double page | Single page
• Notes - includes one page of the information and space to write your own notes.