How to Make Invisible Ink Using Lemon Juice

    by RuthJ

    About the Author

    RuthJ is the author of a student guide to Beowulf, published by Greenwood Press. She is currently writing a book on the technology and material culture of the Middle Ages. She taught her kids at home for many years and learned many offbeat things.


    Unleash your inner secret agent with a quick project using homemade invisible ink. The combination of lemon juice and heat creates a chemical reaction that leaves light brown wherever you touch the paper with the acidic juice. You don't need to limit yourself to cryptic codes either, any design you choose can be created with the citrusy ink.

    Things You'll Need

    • Toothpick, small paintbrush or cotton swab
    • Lemon juice
    • Paper
    • Lamp with removable shade

    Write your secret message or create a design using lemon juice as ink. Apply the juice with a paintbrush, cotton swab or toothpick -- or a combination of tools for more interesting effects.

    Let the lemon juice dry completely. As it dries it should become less visible. You may want to experiment with different types of paper to see which ones will produce a more invisible result. If your writing or drawing is not as invisible as you would like, try again using less juice.

    Remove the lampshade from the light bulb and turn on the bulb.

    To reveal the citrusy art, hold the paper over a lightbulb, running it back and forth slightly over the bulb. allowing the paper to become hot, but not burn. The lemon juice contains carbon atoms that will turn brown as the paper warms.

    Write a letter using regular ink as a "decoy" letter. Put your invisible writing between the lines or on the edges. Only the person receiving the letter will know that it contains a secret message. Anyone else coming across the letter will think it is just a regular letter.

    • Only adults or children over 10 should heat the paper with the light bulb.