Discover the joy of writing an invisible letter with this simple experiment
Has your kid ever wanted to send a secret message to a pal that no one else can read? Yes, it’s possible. As the name suggests, it’s a sort of ink that may be used for writing but does not show up on paper. Well, invisible ink is an old invention that has been used for over 2,000 years. It served a variety of functions, including scheming conspiracies and espionage as well as penning secret love letters. Many different secret ink formulations have been invented since then. The experiment described below will help your kid draft an invisible letter and then reveal the message.
What you’ll need
- Lemon juice
- Few drops of water
- Cotton bud
- Lamp/ light bulb
- Plain white paper
- Bowl/ cup
How-to
Get these on a table and start the experiment with your kid. Here’s a step-by-step guide. Help him follow these
- Squeeze the lemon juice into a bowl or cup and mix in a few drops of water
- Dip a cotton bud into the solution and use it to scribble a hidden message on white paper
- Let the paper dry out and the lemon juice become invisible
- Hold your secret message next to a light bulb to reveal it
How did the message turn invisible?
Well, lemon juice includes colourless carbon molecules at normal temperature. The light bulb's heat decomposes the compounds and releases the carbon. When you write with lemon juice on paper, the acid affects the paper's fibres, causing it to decompose. At the same time, the lemon juice's carbohydrates, as well as the citric acid, are absorbed into the paper. When carbon comes in touch with air, it oxidises and turns brown, revealing the hidden message beneath the scorching light bulb.
Processes used to reveal a message written in invisible ink
To expose invisible ink, a variety of processes can be used, including acid-base, oxidation-reduction, and heat reactions. When an acidic or alkaline component of the ink is made visible by a particular chemical (indicator) that changes colour depending on whether it is in an acidic or alkaline environment, acid-base reactions occur. Oxidation-reduction processes, in which a chemical substance changes colour based on its redox state, can also be used. You can also make use of the fact that some chemical compounds are heat or light sensitive, and will change colour when exposed to these conditions.
Making the ink visible can take various forms depending on the type of chemical reaction the invisible ink is built on, such as adding heat, using a specific chemical, or utilising UV radiation. The secret message is revealed as a result of all of these specific processes.