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Send Secret Messages with Invisible Ink

Most of us will remember how fascinating and fun it was to write secret messages in invisible ink as kids.

There are plenty of great products on the market today but the reality is that there are a few school-friendly methods you can use to get pupils involved in the process while keeping to your budget!

We’ve created this short guide with a few of our favorite methods for making invisible ink. These make for a fun science experiment or even just a great rainy day craft.

Let’s get to it!

invisible ink secret messages

The lemon method

What you will need:

  • Blank white paper.
  • Some lemons.
  • A few bowls.
  • Some cotton swabs.
  • Access to heat (lightbulb, hair dryer etc.)


Squeeze lemon juice into a bowl to create ‘the ink’ and use a cotton swab as a pen. Write down secret messages, let them dry and then hold the paper up to a light bulb or use a hair dryer to reveal the message.


Lemon juice is acidic and weakens the paper where you have used the ink. When exposed to heat the lemon juice burns and turns brown before the rest of the paper thus revealing the secret message.

If this method is a little too messy or too much hassle for your classroom there are two other viable alternatives.


The white crayon method

What you will need:

  • White crayons.
  • Watercolor paint and brushes.
  • Blank white paper.
  • Some water and paper roll to reduce mess.


Instruct kids to write their secret messages on the paper by using the white crayon. Encourage them to use a decent amount of pressure on the paper. Then simply paint over the piece of paper to reveal the message.


Wax is a water resistant material, so when paint is applied it reveals the marks left by the white crayon.


The ink-free method

This is the method with the least mess to create a way to write secret messages

What you will need:

  • Pencils.
  • 2 blank white pieces of paper per kid.


Put the two pieces of paper on top of each other and instruct the class to write a message using pressure on the top sheet.

After the message has been written they can hide or throw away the top sheet. By using the pencil to shade the bottom sheet the hidden message will be revealed.


Through the pressure of the tip of the pencil, it caused an indentation in the bottom sheet of paper.

This changed the surface area of the paper which made it difficult for the lead to be transferred over the indentation, resulting in the secret message being revealed and the illusion of invisible ink.


Fun classroom activities

We at Cool Kid Facts love to produce content for elementary school aged kids and their teachers/parents.

If you liked this invisible ink activity then be sure to check out some of our other science topics. Don’t forget to subscribe to our newsletter to have future activities delivered straight to your inbox!

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