Your little learners may not realize is that the famous invisible ink experiment is more than a fun activity. It’s an opportunity for them to understand the scientific world. You can simultaneously explain invisible ink and the chemical properties of household items.
Like the idea of switching up your STEM lesson plans for a class period? Try our easy-to-follow invisible ink activity for elementary, middle and even high school kids.
How to Conduct the Invisible Ink Experiment in Your Class or Club
Preparation is the key to making sure the invisible ink experiment goes smoothly. Make sure you have the following items:
- A few lemons, cut in half
- A bottle of water
- A few paper cups
- Cotton swabs
- White copy paper
- A lamp with a regular incandescent bulb or a hairdryer set on low
- Safety goggles and plastic gloves for each student
Follow these experiment steps:
- Hand out goggles and plastic gloves to students.
- Divide students into small teams of 2-4 students. Give each group two lemon halves and one cup. Direct them to squeeze the lemon halves into the cup.
- Add about half a capful of bottled water to each team’s cup of lemon juice.
- Ask students to use cotton swabs to write messages or draw pictures on a piece of paper.
- Clean up and move to another activity while the pieces of paper dry.
- Carefully collect all the dry pieces of paper. Bring students together as a whole group.
- One at a time, heat the papers gently over an electric bulb or with the hairdryer. Watch as the lemon juice “ink” becomes visible.
Discussing the Invisible Ink Experiment
After showcasing everyone’s invisible ink papers, ask students why they think the ink turned a different color when exposed to a heating source. Let them talk about it and try to solve the problem logically. Write down their hypotheses on the whiteboard, or put them back into their teams and ask them to brainstorm reasons.
Some students might have an idea about why the invisible ink turns visible or not have the words to explain it. You can explain the fact that lemon juice contains carbon compounds. The compounds aren’t yellow like the lemon — they don’t have a color at all. Therefore, the lemon juice dries on the paper without leaving any marks.
However, those carbon compounds break down when exposed to a heating source. The newly released carbon becomes a brown color as a side effect of oxidation. Now, you have a clever way to send a secret message to a friend.
Bring More STEM Experiments to Your Favorite Students
Looking for other ways to brighten your students’ days with some science? Learn more about our Science Explorers after-school clubs and summer camps!