Make Invisible Ink Using Milk

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.

1. 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.
2. 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.