Ever since people mastered the written word we have attempted to find new ways to hide from others what has been written. One of those ways has been to use invisible ink. Invisible ink is a form of liquid that allows the author to see what he has written, but once it has dried it will become invisible. The written words will become visible again by some means, usually by exposing it to something to activate the so called ink. Some of the easier ways to make invisible ink is by using lemon juice, baking soda and milk. By far the strangest way of making and using invisible ink was by using sperm, that’s right, semen and MI6 tried just that method during the First World War. But want to know something even weirder? It worked incredibly well. Semen, sperm if you will, can be used by anyone as invisible ink.
In June 1915, the deputy head of intelligence at GHQ France, wrote in his diary that the first chief of the SIS, Mansfield Cumming (coincidence?) was “making enquiries for invisible inks at the London University”. Later that year he heard from the chief that the best invisible ink was semen. Semen, it seemed, did not react to one of the main methods of detection, iodine vapor, and was readily available.
This method of using semen as invisible ink had a few drawbacks though. The poor fellow who discovered its use had to be moved to a different department as he had become the butt of jokes. Additionally to this problem, at least one agent had to be reminded to use fresh supplies of the “ink” after correspondents began noticing an unusual smell.