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By Ruth Barnard

Here we show you how to make invisible ink and how to write and reveal your hidden message, we also talk about the science behind the magic...

Difficulty: Easy

Time: 5 - 10 minutes



What you need:

  • 1 tbsp baking soda

  • 2 tbsp water

  • Paper

  • Your choice of writing tool, eg: paintbrush, cotton bud or quill

  • Purple grape juice

  • Two small bowls


What to do:

1. To make the invisible ink use a small bowl to mix the water and baking soda. Stir together.

2. Write words on your paper with your ink and choice of magic ink pen (look below for ideas of what to write.)

3. Wait for the ink to completely dry and then brush off any excess baking soda.

4. Now paint over the paper with grape juice and watch your writing or picture magically appear!



What to Write



The Science Behind the Magic

The invisible words appear because of a chemical reaction between the grape juice and the baking soda. The grape juice is an indicator that shows us if an alkali (also called a base) is present by turning blue.

What is an indicator?

An indicator is something that can change colour depending on whether it is in a base or an acid substance. Scientists often use litmus paper as an indicator. This paper turns blue when in a base and red in an acid substance. It can also turn green which shows the substance is neutral (not an acid or base).  

In this case purple grape juice is a natural indicator which turns bluish purple/black when reacting with a base. The invisible ink we have created is made up of baking soda (which is a base) and water (which is neutral). Therefore, when the grape juice indicator reacts with the invisible ink it turns it dark blackish blue.

Other Natural Indicators

There are other juices such as red cabbage, beetroot juice and tea which are also natural indicators. A fun indicator plant is the Hydrangea, when it is in acidic soil the Hydrangea flowers will be pink or red and when it is in alkaline soil they will be blue.

Extra Experiments

Test out the grape juice indicator by adding lemon juice or white wine vinegar to a mix of grape juice and baking soda you should see it fizz and bubble and then change from bluish purple to a light pink or reddish purple. It can make a mess so work on an easy to clean surface. Happy experimenting!


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