Send secret messages with invisible ink

Do you like playing spies with your friends or siblings? Want to be able to write secret messages? Here are a few ideas for making invisible ink to create top-secret notes.

Heat-activated
Mix together milk and white vinegar or lemon juice in a small bowl. Get a sheet of white paper and a writing utensil like a cotton swab or a small paintbrush. Soak the tip of the writing utensil in the liquid, then write your secret message.

The invisible ink must dry completely before you try to decode it. The person who receives the message must place the paper over a heat-producing light bulb or another heat source. If using a candle, do so only with permission and adult supervision. The heat will reveal the hidden text.

Liquid-activated
Combine equal parts of water and baking soda in a small bowl. Dip your writing utensil in the mixture and create your message. Once the invisible ink has dried completely, explain to the person receiving it that they need a paintbrush and a glass of grape juice. The hidden text will appear when they cover the paper in a thin layer of juice.

You can also write your message with a white pencil or wax crayon and replace the grape juice with water-based paint to achieve the same effect.