Invisible ink has been used by spies and secret lovers alike for centuries to transmit hidden messages to their partners. Invisible ink isn’t just something you see in James Bond movies; hundreds of liquids, from fruit juices to household liquids, to specially formulated chemicals, can be used as invisible ink. In this science experiment, become a master of ‘steganography’ by making your own invisible ink from baking soda and send secret messages to your friends:
WHAT YOU NEED:
Purple grape juice Baking soda Tap water Cotton swab White writing paper
HOW TO PROCEED:
1. Thoroughly mix equal parts tap water and baking soda powder in a container until dissolved.
2. Use a cotton swab or fine paintbrush to write a message onto the white writing paper, using the baking soda and water solution as invisible ‘ink’. Make sure to dip the swab into the ‘ink’ often so that the recipient can read the message with ease.
3. Allow the ‘ink’ to dry out thoroughly until the writing becomes completely invisible. Your secret message is now ready to be delivered to the intended recipient.
4. One way for the recipient to read the message is to hold the paper up to a heat source, such as a light bulb, hot iron or it can even be placed in an oven. The baking soda will cause the writing in the paper to turn brown to enable the recipient to read the message!
5. A second method to read the message is to paint over the paper with purple grape juice. The message will appear in a different colour!
This science experiment works because substances such as vinegar or baking soda are either mildly acidic or alkaline, and such an acid or base weakens paper. The base from the baking soda remains in the paper after the water has evaporated and the paper has dried. When the paper is then held near a heat source such as a light bulb or hot iron, the alkaline parts of the paper burn or turn brown before the rest of the paper does, revealing the message written on the paper!
If you are using the grape juice method to reveal the message, the baking soda and grape juice react with each other in an acid-base reaction, producing a colour change in the paper to enable the recipient to read the secret message. Grape juice concentrate results in a more visible colour change than regular grape juice. There are many other household liquids that can be used to make invisible ink. Using the heat method, you can also use white wine, vinegar, apple juice, and even milk!