Experiments
Oxidation (heat causes the juice to darken).
Lemon (or lemon juice), paper, cotton swab or paintbrush, a lamp or candle (with adult supervision).
Squeeze lemon juice into a small bowl. Use the swab to write a secret message on the paper. Let it dry. To reveal, gently heat the paper by holding it near a light bulb or carefully over a candle flame (adult supervision required).
Eco-Twist: Use scrap paper and compost the lemon peel afterward.