WARNING! This experiment is dangerous! You should NOT perform this at home. ONLY carry out this experiment, if you are a trained chemist, and you understand local safety and legal requirements, which are required to perform such experiments
- Fill 1/4 of an empty plastic vial with 1% tannin solution (about 2 mL).
- Dip the brush into the tannin solution.
- Write a secret message on yellow paper between the lines or on any blank space.
- Let the paper dry. It will take 2–3 minutes.
- Moisten a cotton pad with 0.1M iron (II) sulfate solution FeSO4. You will need 15-20 drops.
- To reveal the message, rub the paper surface with the cotton pad.
- Wash the brush with water for use in future experiments.