Invisible ink

Sympathetic ink is a solution for writing information on paper. They differ from ordinary ink in that the message written with them cannot be seen until certain conditions are applied, be it heat, light, etc. This method of transmitting information has been one of the main elements of encryption at all times. As a rule, secret information was first written on a blank sheet of paper using sympathetic ink. After drying, a regular message was applied on top of the transparent inscription using simple visible ink. Such letters, as a rule, were heated to create a secret code, and then the sheet was destroyed. There are many different recipes for invisible ink, including purely chemical ones, which are sold in ready-made form today in office supply departments. However, you can prepare such spy ink yourself.
To do this you will need: Regular baking soda, some warm water, a spoon, a toothpick with cotton wool (you can also use a cotton swab or a refillable fountain pen), a sheet of paper and a candle.



Step 1. Baking soda must be diluted in water to form a concentrated solution.Allow the mixture to cool slightly. It is not necessary to ensure complete dissolution of the soda.



Step 2. If you have a fountain pen, you can fill it with freshly prepared solution.



Then we use it. If you don’t have such a device at hand, you can use a cotton swab or a regular toothpick with a piece of cotton wool at the end.



It is necessary to dip it in an aqueous solution of soda and squeeze it lightly. After this, you can safely write a message on a blank sheet of paper.



Step 3. It is advisable to let the ink dry a little before starting to develop the letter. In order for the secret record to become visible, the sheet with it must be held over heat. It could be an iron, gas or electric stove, but in our case we used an ordinary candle. To prevent the paper from catching fire, you need to move it lightly over the flame.



Step 4. If everything is done correctly, then after about 30-40 seconds a yellow-brownish inscription will appear. Ready! The inscription is revealed. You can also heat a sheet with a secret recording on a battery, but this will take much longer, and the recording itself will not be as bright.




You can also use lemon juice or concentrated vinegar instead of soda solution, however, these substances leave slightly visible marks on the paper, which no longer corresponds to the “secret” stamp.