September 21st, 2010
We probably shouldn't hold out breath waiting to see this bit of tradecraft feature in a James Bond script:
In June 1915, Walter Kirke, deputy head of military intelligence at GHQ France, wrote in his diary that Mansfield Cumming, the first chief (or C) of the SIS was "making enquiries for invisible inks at the London University".
In October he noted that he "heard from C that the best invisible ink is semen", which did not react to the main methods of detection. Furthermore it had the advantage of being readily available.