Grade 4: Science

Invisible Ink! 

Observe a chemical reaction in action, with homemade invisible ink!  

Materials:  

• Fresh lemon juice 
• Water 
• Q-tip 
• Blank piece of white paper 
• A heat source, like a hair dryer

Squeeze lemon juice into a bowl and add water—just a few drops. Use the Q-tip to write or draw your message on the piece of paper. 

When the paper has dried and you’re ready to reveal the hidden message, blow hot air on it with the hair dryer. As the paper heats up, the invisible ink will turn brown, revealing the secret message.  

How does it work? Lemon juice contains a carbon compound that is invisible at room temperature. Heat breaks down that compound and releases the carbon. When the carbon interacts with the air, it oxidizes and turns brown. This oxidation is a chemical reaction!   

Throughout the experiment, ask your child about the process to encourage scientific thinking. As the message appears before your child’s eyes, explain what is happening.  

To extend their thinking, do the experiment again but change one attribute at a time to see how it affects the outcome.  

Here are some ideas to get you started:  

• What do you think will happen if you use colored paper instead of white paper? 
• What do you think will happen if you don’t let the paper dry before heating it up? 
• What if you wrote the message with orange juice—do you think the outcome will be the same?  
• Can you think of other kinds of chemical reactions you have observed? (Maybe rust on a fence or cake batter turning into a cake in the oven.)  

Actively engaging in the scientific method, with simple materials kids are familiar with, is a powerful way to help them connect to the scientific concepts they are learning about in school. Plus, including them in every step of the process empowers kids to be curious, practice flexible thinking, and develop problem-solving skills.