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.