Incredible Chemical Spectacles

Invisible Ink

Have you ever wanted to write a secret message to someone? Borrow a tool from spies: invisible ink. With invisible ink, you can write a message that can only be read by someone who knows the secret to revealing it. Many invisible inks rely on a chemical reaction to become visible. Our invisible ink can be revealed with red cabbage juice.

Take Note!

Safety first in the kitchen! Always get an adult to help you when you cook.


Invisible Ink

  • 3 tbsp. (45 mL) baking soda
  • ¼ cup (60 mL) water
  • blank paper
  • two cotton swabs or paintbrushes
  • 2 bowls
  • ¼ cup (60 mL) red cabbage juice

Red Cabbage Juice

  • 10–15 red cabbage leaves
  • 2 cups (455 mL) boiling water
  • 1 kettle
  • 1 bowl

Let's Get Started

Making red cabbage juice

  1. Use the kettle to boil 2 cups of water.
  2. Place 10–15 cabbage leaves in the bowl, and pour the boiling water over the leaves. Let cool for one hour.
  3. Strain out the cabbage leaves.
  4. Store the juice in the freezer in small containers, so that you can thaw some every time you need to reveal a secret message. The cabbage juice will rot and become very smelly if left in the fridge or on the counter for too long.

Making invisible ink

  1. In a bowl, mix the baking soda and water.
  2. Use a cotton swab or paintbrush to write a message on the blank piece of paper using the baking soda and water mixture as ink.
  3. Leave the paper to dry.
  4. To reveal your message, dip another cotton swab or brush in a bowl of red cabbage juice and rub it over the message.

What Happened? Let's Check the Results

Baking soda mixed with water forms a type of substance called a base. It is possible to tell if a substance is a base or not with red cabbage juice, because red cabbage juice changes colour from purple to greenish-blue when it touches a base. In this experiment, the cabbage juice reacts with the dried baking soda and changes colour, revealing the secret message.

Red cabbage juice will change to a different colour when it is mixed with acids. Try mixing a little red cabbage juice with an acid such as vinegar to see what happens.

Take Note!

Make sure your message is written with as much ink as possible, but watch out! Paper can rip when it's too wet.

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