Milk is an effective and readily available form of invisible ink. Here's how to use milk as invisible ink to write and reveal secret messages. I've also included 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.
All About Invisible Inks
