Invisible Ink Chemistry

Invisible ink is fun to experiment with- you can pretend that you are a secret agent and write secret codes on paper. It turns out that you don’t need to buy fancy invisible ink to do this, because the chemical properties of lemon juice prove that it is a very effective invisible ink. This is because it oxidizes whenever it comes near heat, which causes it to become darker in color. So, when lemon juice is originally used to write a message on paper, it is invisible because of the clear color of the juice, but once it is brought near heat, then its darkening causes the message to be revealed. Oxidation is a chemical reaction with oxygen, and another example of this is whenever iron rusts, creating a reddish color.

Now, let’s create your own lemon juice invisible ink:

• Mix lemon juice in a cup with a little bit of water.

• Dip a cotton Q-tip into the mixture and use it to write a message on a piece of white paper

• Wait until it dries

• Use adult supervision for this step if necessary: Hold the paper near a lightbulb or other safe source of heat until the message shows up.

Picture Source: Wiktionary