Materials
- ¼ cup baking soda
- ¼ cup water
- Small cup
- Cotton swab
- White paper
- Grape juice (purple works best)
- Spoon
Instructions
- In a small cup, mix ¼ cup baking soda with ¼ cup water. Stir until the baking soda dissolves as much as possible.
- Dip a cotton swab into the baking soda solution.
- Use it to write a message or draw a picture on the white paper.
- Let the paper dry completely. The message will become invisible.
- Pour a small amount of grape juice into a separate cup.
- Lightly brush or dab the grape juice over the paper.
- Watch as the secret message appears.
What’s going on?
- Baking soda (sodium bicarbonate) is a base. When you write with the baking soda solution, it dries invisibly on the paper but leaves behind a basic residue.
- Grape juice contains natural pigments called anthocyanins. These pigments change color depending on whether they are in an acidic or basic environment.
- When grape juice is brushed over the paper:The anthocyanins stay their normal color on untreated paper. Where baking soda is present, the pH is higher (more basic). In these basic areas, the anthocyanins change structure, causing a visible color change.
- This difference in pH causes the hidden writing to appear, revealing the secret message.
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