Mystery Writing: Write and develop a secret message

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Learners write an invisible message using lemon juice on a piece of paper. They then develop the message by soaking the paper in a dilute iodine solution. The iodine stains the paper blue, but the vitamin C in the lemon juice prevents the iodine from reacting, leaving a white message. Care should be taken in this activity since iodine can stain skin and clothing. This activity (located on page 2 of the PDF) is one of three activities in the Take Home guide for the Everyday Chemistry unit in OMSI's Chemistry Lab. The PDF includes two additional activities: Iron in Cereal and Spicy Indicator.

Quick Guide

Preparation Time:
10 to 30 minutes

Learning Time:
10 to 30 minutes

Estimated Materials Cost:
$1 - $5 per student

Age Range:
Ages 6 - 14

Resource Types:
Activity, Experiment/Lab Activity


Materials List (per student)

  • 2 tablespoons lemon juice
  • small cup
  • small brush or cotton swab
  • paper
  • shallow bowl or pie plate
  • water
  • rubber gloves
  • 10 drops tincture of iodine (from drugstore)


  • Physical Sciences
    • Chemistry
      • Chemical Reactions
      • Acids and Bases

Informal Categories

  • Crime Science
  • Food and Cooking


To use this activity, learners need to:

  • see
  • see color
  • read
  • touch

Learning styles supported:

  • Involves hands-on or lab activities


This resource is part of:

Access Rights:

  • Free access



Funding Source:

  • National Science Foundation