Six of the oldest files held by the agency, which predate it by several decades, were made public this week.
One paper from 1918 lists the chemicals and techniques used to create “secret writing”. Another from 1914 and written in French gives the formula the Germans were believed to have used for their invisible ink.
“When historical information is no longer sensitive, we take seriously our responsibility to share it with the American people,” said Leon Panetta, the CIA director.
The documents, which were originally kept by the Office of Naval Intelligence before even the Office of Strategic Services, the CIA’s predecessor, was established, offer a fascinating glimpse into spycraft from another age.
Some handwritten, they reveal chemical methods used by intelligence agents to open sealed envelopes without being detected and carry warnings such as:
“Do not inhale fumes.”
The papers give a glimpse into a secretive wartime world. One suggests that messages should be passed by soaking a handkerchief or collar in a mixture of nitrate, soda and starch and then drying the fabric. The chemicals would come out when the cloth was put in water and that liquid would become invisible ink for message writing. The person receiving the message could then read the words by applying iodide of potassium.
Some 50 scenarios for using the ink were suggested, including “placing writings under postage stamps, wrapping messages in medicine capsules and engraving messages on toenails”.
A chemist who provided some of the chemicals warned that the ink might be toxic enough to corrode a steel pen and advised that a quill be used instead.
Steve Aftergood, of the Federation of American Scientists, was unimpressed by the CIA’s “openness”. “Invisible ink was rendered obsolete by digital encryption long ago,” he said.
Invisible ink – How starch helped secrets disappear
1. Put a tablespoon of starch into a tumbler of water and boil it. Allow the water to cool and then add 10 grams of nitrite of soda, a lawn fertilizer available in garden centres.
2. Soak a handkerchief or starched shirt collar and allow it to dry.
3. Add the material to water and the chemicals will be released, creating invisible ink. Write a message with it, ideally with a quill.
4. The person who receives the message should apply iodide of potassium, used in disinfectants and chemical hair treatments, to make it visible.
Filed under: Spy Kit, Unknown History Tagged: | Central Intelligence Agency, Federation of American Scientists, Invisible ink, Leon Panetta, Office of Naval Intelligence, Office of Strategic Services, United States, World War I