Secret ink

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When invisible inks or sympathetic inks (formerly chemical inks) are inks designated that are either not visible or change their properties after some time.


As early as 50 AD, Pliny the Elder was using secret ink made from the plant milkweed (Tithymalus). The text only became visible when the parchment was heated over the fire. Secret inks were particularly popular in the 17th and 19th centuries. The term "sympathetic ink" (from Greek sympatheia "affection") also comes from this time , as it was often used to write love letters . Ovid already recommended milk to the Roman women in order to make their correspondence invisible to unauthorized persons; all you have to do is sprinkle coal powder on it. 1653 The Frenchman beat Pierre Borel in front, with a lead acetate to write and the writing with liver of sulfur solution to visualize. Jacob Waitz , personal physician in Gotha , discovered the property of cobalt chloride (chlorobalt) to produce lettering that is almost invisible after it has dried out, but that becomes clearly blue when it is heated and disappears again when it cools.

Later, inks were developed that can be made visible with acid or UV light , or that disappear after a while. During the Cold War, secret services used special "dry" procedures so that agents did not have to carry suspicious vials for the secret ink with them. Even nowadays, the secret inks have not gone out of fashion, as children like to use them for "secret" messages.

Examples of simple secret inks

See also


Individual evidence

  1. Silk scarf for secret writing. In: German Spy Museum. Retrieved on July 13, 2020 (German).

Web links

Wiktionary: Secret ink  - explanations of meanings, word origins, synonyms, translations