Follow these easy instructions to make nontoxic invisible ink, in just a few minutes, using baking soda (sodium bicarbonate.) The advantages of using baking soda are that it's safe (even for kids), simple to use, and readily available.
- Baking soda
- Light bulb (heat source)
- Paintbrush or swab
- Measuring cup
- Purple grape juice (optional)
Make and Use the Ink
- Mix equal parts water and baking soda.
- Use a cotton swab, toothpick, or paintbrush to write a message onto white paper, using the baking soda solution as "ink."
- Allow the ink to dry.
- One way to read the message is to hold the paper up to a heat source, such as a light bulb. You can also heat the paper by ironing it. The baking soda will cause the writing in the paper to turn brown.
- Another method is to paint over the paper with purple grape juice. The message will appear in a different color. The grape juice acts as a pH indicator that changes color when it reacts with the sodium bicarbonate of baking soda, which is a base.
Tips for Success
- If you are using the heating method, avoid igniting the paper; don't use a halogen bulb.
- Baking soda and grape juice react with each other in an acid-base reaction, producing a color change in the paper.
- The baking soda mixture can also be used more diluted, with one part baking soda to two parts water.
- Grape juice concentrate results in a more visible color change than regular grape juice.
How It Works
Writing a secret message in baking soda solution slightly disrupts the cellulose fibers in paper, damaging the surface.
When heat is applied, the shorter, exposed ends of the fibers darken and burn before the undamaged sections of paper.
If you apply too much heat, there's a risk of igniting the paper. For this reason, it's best to use either the grape juice chemical reaction or else apply a gentle, controllable heat source.