Invisible Writing

Science Activity

Students will write secret messages with invisible ink, exchange them, and reveal the secrets.



  1. Give each student some scrap paper, a pencil, a thin sheet of white paper, and a toothpick. Have students write their names on the thin paper.

  2. Next, have them compose a secret message for a classmate on the scrap paper.

  3. Fill a small cup with lemon juice or vinegar for each student. Tell students to dip the toothpick into the liquid and use the toothpick to write their message on the thin paper. Allow time for messages to dry completely.

  4. Have students exchange their invisible messages and make them appear. To do so, have each student hold the paper near the glowing light bulb. (Remind students that a 100-watt bulb is very hot and to be careful when holding the paper near it.) They'll be amazed as the mystery message appears.

Lemon juice and vinegar are mildly acidic, and acid weakens paper. The acid remains in the paper even after the juice or vinegar dries. When the paper is held near a hot light bulb the treated portions of the paper burn, and turn brown, more readily than the untreated portions.

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