A treasure map with invisible ink

Invisible ink is very useful for drawing treasure maps or writing secret messages. Only those who know chemistry will find a way to reveal your message. Let’s use onion juice to prepare the invisible ink.

You will need:

From 6 years

Difficulty : medium

This experience requires the help of an adult

Let's experiment

cut onions

Peel your onion and cut a quarter of it into very small pieces.

collect onion juice

With the garlic press, mash the onion pieces and collect the juice drops in a bowl.

write with the invisible ink of onion juice

With a toothpick, draw or write the messages you like using onion juice like ink.

When finished, let your sheet of paper dry for 5 to 10 minutes.

With the help of an adult, turn on an electric hot plate and allow it to heat for 2 to 3 minutes.

Then ask an adult to position the sheet on the heater plate and observe what is happening.

make the drawing appearing with the heat

Et voilà 😊 Nous, nous avons fait une carte au trésor.

invisible ink visible
treasure map with invisible ink
treasure map with invisible ink

Understand the experiment

It smells like onion!

Onion juice, but also lemon juice or vinegar, are organic compounds. They are rich in acid.

At room temperature, these juices are colorless. Under the action of heat, these juices oxidize and decompose. That causes a color change. From invisible, the ink becomes brown or black. It’s your turn to be the spy!

You can use other heat sources like a candle to make your drawings appear worthy of spy movies.

Did you know?

The first secret messages in invisible ink date from Ancient Greece (-500 BC)

Spies used invisible ink during the First World War or in magic tricks. But the very first to have used it were the ancient Greeks and Romans who used the milk of a plant, the tithymalus. There are several invisible inks based on acids or based on the use of chemicals.

tithymalus

Challenge

Alternatively, you can test the juice of certain fruits, like lemon or cherry for example. But also soda diluted in a bit of water

Experiments

The crazy match

Have you ever noticed that your hair goes all over the place when you put on your jumper? Or did you ever get a shock when you kissed someone? The culprit is static electricity. And you are going to use this hair-raising concept to make a match move without touching it. Shall we take up the challenge? […]

Experiment decode messages with a red filter
Experiments

Decode messages with a red filter

Do you want to send secret messages to your friends, without anyone else being able to read it? Or even send a secret invitation to a lover? Play with light and color transmission to hide your messages. It’s your turn to play! […]

Chemistry

Create your homemade fire-extinguisher

With this experience, you will understand that fire needs oxygen and that in the absence of it, the candle goes out. The trick is therefore to eliminate the oxygen around the candle. Carbon dioxide is an inert gas used in fire extinguishers. When it replaces the air around the candle … the fire goes out. Try to make your own fire extinguisher. […]

Curiokids, official partner of Enseignons.be