We have the best recipes and tricks on how to make secret ink. We will also show you how you can make secret writing visible. With these tips, you can compete with Sherlock Holmes!

There are different forms of secret ink that you can easily make yourself. Here we would like to show you two natural formulas with simple home remedies such as lemons, onions, and milk. We also have a chemical version of making secret ink ready for you.

A popular game among children

With a look at Room Escapes, the Sherlock Holmes series, and the boom in detective games on the German board game market, it becomes clear that the age of detective joy among children and adults is far from over. A detective or secret agent party is also ideal for a theme party for children’s birthday parties. Then how cool would it be to write the invitation with a cipher as the first puzzle? You can easily do it yourself with home remedies. As? We’ll show you here.

1) Lemon or onion juice as a secret ink

You can write invisibly with lemon juice or onion juice. You can make the onion juice secret ink by peeling and grating the onion and then squeezing it through a cloth. The text and the secret writing become visible again when the paper is heated. This can be done either by ironing with a warm, not hot iron, by holding the paper to a light bulb or by placing it on the heater, by blow-drying it briefly, or by holding it briefly over a tealight. However, children should never do this unsupervised.

2) milk for cryptography

A second option is to use milk as a secret ink. You can easily take standard cow’s milk and apply it with a brush or a wooden skewer. The invisible milky writing becomes visible through the application of cigarette ash or the powdered graphite of a pencil from a pencil sharpener.

3) Make Nitrate of Cobalt Oxide for Secret Ink

Chemically you can get nitrate of cobalt oxide in the pharmacy, which you can dissolve in water to get an invisible secret ink. When heated, this secret ink appears red and when it cools down, the writing automatically becomes invisible again. In principle, the production of this secret ink works in a similar way to the home remedies lemon or onion juice.