Science Experiments for Kids: How to Make Invisible Ink

2/27/20 - By Ally Noel

This low-tech invisible ink science experiment lets kids send secret messages to friends and family. All they'll need is a little lemon juice or milk. We decided to try both versions of this invisible ink experiment to see if the results were any different. 

Commonly found household items make up the ingredient list, including juice, milk, honey, and vinegar. At room temperature, these compound liquids are colorless, making them perfect for invisible ink fun. Put them in contact with heat and the oxidization process turns them various shades of brown, aka, the ink appears! Read on for step-by-step instructions on how to make invisible ink with your kids.

Find more science experiments for kids in our STEM Activities Guide.

We used milk and lemon juice to create our invisible ink. 

Step 1

Gather your ingredients and tools. For this experiment, you need a piece of paper, a cotton swab, a heat source (a lamp or electric stove works), and milk or lemon. 

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Draw or write your secret message. 

Step 2

If you are using lemon juice, squeeze your lemon into a glass. You can mix it with a little bit of water. Dip your cotton swab into the milk or lemon juice and start writing your message. Let your message dry completely.

Apply heat to get the secret message to appear.

Step 3

Once dry, an adult should hold the sheet of paper over a heat source. We used an electric stovetop. You can also use a lamplight or blow-dryer.

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Your messages will appear like magic! 

Step 4

As the milk or lemon “ink” heats up, it will oxidize and turn brown. You can try this experiment with other substances such as vinegar, honey, or orange juice.

Find this science experiment and more ideas in our 63 Easy Science Experiments for Kids article.

All photos by the author