Brit Spies Used Semen as Invisible Ink Intelligence chief 'delighted' by discovery By Emily Rauhala, Newser User Posted Sep 22, 2010 8:22 AM CDT Updated Sep 26, 2010 9:31 AM CDT 12 comments Comments Well, we knew spies were resourceful... (AP Photo/Sony Pictures) (Newser) – More from the secret world of Britain's MI6: The spy agency apparently used semen as invisible ink during World War I. A new history claims that Chief Mansfield Cumming advised an intelligence officer that the substance makes "the best invisible ink," notes the Telegraph. Another staff member recalls Cumming's 'delight' at the discovery. Presumably the chief's euphoria faded when at least one agent had to be told to use only fresh "ink" (to avoid unusual smells) and another had to be transferred because he was being mocked for "discovering" the technique. The book's author told the AFP that "the real James Bonds are in fact more interesting than the fictional ones." Sounds like it.