Secret Writing Inks and their Decipherment Techniques

When a spy or any agent has to send any secret message, they transfer it through written text to conceal their writings. Some precise methods are used to hide the written text, i.e., secret inks. It can be deciphered using specific techniques. In the upcoming sections of this article, we will study secret writing, techniques involved in secret writing, and methods to decipher it.    

Secret writing is a way to communicate through writing by hiding the written text, by encoding or deciphering. It is an art to hide or cover writing. Sometimes Ciphers and Codes are placed mistakenly under the “secret writing” heading. However, it is precise only by taking the expression in its most ordinary sense because the writing is covered in any way. Ciphers and codes hide the definite message.

Techniques involved in writing secret texts are carbon copies and invisible ink. This way of sending a text is used from ancient times until the primary twentieth century; modern ways like microdots conceal secret writing. Along with the above topics, we will also discuss its history to enhance your knowledge of secret writing.

History of Secret Writing

In his respected past, Herodotus styled a way to write secretly used in the Persian battles. When the Persian emperor was getting ready to march on the city-states of Greek in 480 B.C., a simple refugee name Demaratus read the plans forced to inform his countrymen. The issue was how to convey the message without the interception of Persians. Demaratus made out a clever answer to this question.

He scratched out some wax from the wooden tablets, wrote the message beneath a wood, poured out hot wax on tablets again. However, the countrymen did not have the advantage of knowing how to decipher the secret text. They finally revealed the text because of the gods and read it. Therefore, the Greeks started preparing for the future invasion.

Techniques to Hide and Decipher the Written Text

1. Invisible Ink

A form of secret writing children is aware of due to its involvement in their projects. It uses citric juice such as lemon juice, the most appropriate option as it dries without leaving any sign of its usage. Juice act as ink, used on a tool (fine stylus). After it dries, acid is still present on the paper. When we apply heat, the hidden text is exposed.

When the paper is exposed to U.V. light, the invisible ink emits fluorescence in a visible region, making the secret text visible. 

Another type of this ink is milk, a mild acid. Apple juice, vinegar, or white wine can also be used. In history, saliva, sweat, urine, etc., were used as invisible ink. After they adhere to the surface of the paper, the ink weakens it even after their evaporation. 

We can also use a mixture of baking soda and water. After it dries, apply grape juice by brush. The acids of grape juice react with the base, i.e., baking soda, and expose the message. 

2. Carbon Copies

In the period between the late 19th & early 20th century, carbon copies were a way of secret writing. Central Intelligence Agency includes a method unlike the current methods while one signs a credit-card receipt. The back is infused with graphite. While signing the receipt front, the applied pressure transferred graphite on the second page leaves an impression written by a pencil.

The CIA type of this method involves a paper that contains a specific chemical that becomes invisible when it is transferred to the second paper. It engraved the secret writing on the backside of the envelope, which is mailed to agents via regular channel. Water and heat develop or exposes the secret writing, which is then read.