“There are a number of other methods used by spies and smugglers, according to the skill and education of the criminals, such as placing writings under postage stamps, wrapping messages in medicine capsules and engraving messages. The pamphlet, listing 50 possible scenarios in which invisible ink could be employed, was prepared by a handwriting expert in San Francisco. postal inspectors how to detect secret ink.

One document listing seven formulas is on Department of Commerce letterhead, and a chemist at the Bureau of Standards recommends that some of the invisible ink solutions be used with a quill pen rather than a steel pen because of the risk of corrosion.Īnother document in the collection was intended to teach U.S. The six documents were first held by the Office of Naval Intelligence during World War I, and at least one was obtained from the French.īut, as the CIA said Tuesday, the intended recipients of all this secret stuff are not always clear. They will also be available at the National Archives. One document lists chemicals and techniques to create invisible ink for what is charmingly called “secret writing.” Another document, from June 1918 and written in French, provides the formula the Germans apparently used for their invisible writing during World War I.Īll of the documents can be viewed at in the site’s Freedom of Information Act Electronic Reading Room. “When historical information is no longer sensitive, we take seriously our responsibility to share it with the American people,” CIA Director Leon Panetta said in a statement announcing the release.

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