Invisible Ink: A Citrus Painting Experiment
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Recipe type: Science
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Making time: 
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Lemon juice is acidic, and acid weakens paper. When paper is heated, the acid burns and turns brown before the paper does.
Ingredients
  • Lemon or Lime Juice
  • Paper
  • Paint brush or Q-tip
  • Iron
Instructions
  1. Squeeze lemon or lime into a bowl.
  2. Paint the juice onto your paper with a paint brush or Q-tip.
  3. Wait for the paper to dry.
  4. Heat the paper with an iron, hair dryer, light bulb, or other heat source. Be careful that you don't hold it there to long, as it could burn the paper.
Notes
Experiment with other liquids: milk, orange juice, white wine, vinegar, and apple juice are good bets.
Recipe by TinkerLab at http://tinkerlab.com/invisible-ink-a-citrus-painting-experiment/