If you’re concerned that the National Security Agency is reading your private thoughts, Professor Kristie Macrakis has a novel idea: invisible ink. The School of History, Technology and Society faculty member is an expert in the history of science and espionage. She describes ways people have historically got their message across, without making it apparent.
In ancient Rome, the love poet Ovid wrote a racy manual on the Art of Love and appears to be the first person use milk to hide secret messages. He tells us:
A letter too is safe and escapes the eye, when written in new milk:
Touch it with coal dust and you will read.
Well, you don’t need to use coal dust after pulling out the milk cart. You can simply heat the message and it will become visible. Of course, if you write the message on a body you might try a glutinous substance like ashes or dust to read the message, as you don’t want to burn your partner.
Lemon juice is another household invisible ink item. By the 16thth century many people used lemon or lime juice to write secret messages. Spies used it, prisoners used it and lovers used it.
To read more about invisible ink and secret writing, click here for the full blog post.
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