How to Make Secret Ink
- 1). Choose an ink source. Fruit juice or milk will both work. Put the juice or milk in a bowl.
- 2). Dip a paintbrush or cotton swab into your secret ink and write your message on plain white paper. Allow it to dry for a few minutes.
- 3). Hold the message over a heat source to reveal the the message. The juice or milk acts as an acid and the heat reacts to the acid, weakening the paper in those spots where you have written your message.