During World War I, British spies were looking for the perfect invisible ink and thought natural fluids would be ideal. What’s the big deal about using sperm to write letters? … Semen fails the iodine vapour test, which previously turned all known invisible inks brown.
During World War I, British spies experimented with a variety of invisible inks. One spy was ecstatic in 1915 when he discovered a simple way to make one. What is the secret ingredient in his recipe? Semen.
When presented with this novel method of creating invisible ink, Captain Sir Mansfield Cumming, the founder and head of MI6 at the time, reportedly declared “every man his own style.” The only issue? The letters would become quite pungent if they weren’t fresh.
One spy stationed in Copenhagen had apparently built up a supply of semen in a bottle, and his letters, in particular, were smelling foul. Captain Cumming insisted that if this method was to be used, “each letter would require a new operation.”
However, life quickly turned sour for the unnamed officer who discovered this homemade invisible ink. When he told his fellow spies, they laughed at him so much that he had to be transferred to a different office.
Michael Smith’s book Six: The Real James Bonds 1909-1939 includes an excerpt from a letter written by one of Cumming’s officers, Frank Stagg, about the semen ink method:
Secret inks were our stock in trade and all were anxious to obtain some which came from a natural source of supply. I shall never forget [Captain Cumming’s] delight when the Chief Censor [Frank] Worthington came one day with the announcement that one of his staff had found out that semen would not respond to iodine vapour and told the man that he had had to remove the discoverer from the office immediately as his colleagues were making life intolerable by accusations of masturbation. The Old Man at once asked Coney Hatch [lunatic asylum] to send female equivalent for testing and the slogan went round the office — every man his own stylo. We thought we had solved the problem. Then our man in Copenhagen, Major [Richard] Holme, evidently stocked it in a bottle, for his letters stank to high heaven and we had to tell him that a fresh operation was necessary for each letter.
It’s unclear what the “female equivalent” was or how it would be obtained in an insane asylum, but one can only imagine a horrifying scenario involving vulnerable people.