Science, Tech, Math › Science Make Invisible Ink Using Milk Easy Invisible Ink from the Kitchen Share Flipboard Email Print You can use milk as an invisible ink to write secret messages. Photodisc, Getty Images Science Chemistry Projects & Experiments Basics Chemical Laws Molecules Periodic Table Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 10, 2020 Milk is an effective and readily available form of invisible ink. Write the message with milk, let it dry, and watch it disappear. Here's how to use milk as invisible ink to write and reveal secret messages. Also included is an explanation of how milk works as an invisible ink. Dip a paintbrush, toothpick or stick into milk and write your message on paper. You'll be able to see the damp message, but it will disappear once the paper dries.Reveal the invisible message by holding the paper over a lit light bulb or other heat source. How It Works The substances in milk weaken the paper and also may be more susceptible to heat than the paper, so although the message dries clear, the paper weakens and darkens where the milk was applied. Other common kitchen ingredients you can use for invisible ink include lemon juice, baking soda, and even urine.