CIA Spills the Beans on Invisible Ink Secret Recipe (Washington Post)

If you can lay your hands on some copper acetol arsenate, you can make invisible ink using the CIA’s formerly super-secret recipe. It’s one of the CIA’s six oldest classified documents released this week.

“When historical information is no longer sensitive, we take seriously our responsibility to share it with the American people,” says CIA Director Leon Panetta in The Washington Post.

The documents can be viewed on the CIA’s website’s Electronic Reading Room. They will also be available at the National Archives.


  1. Herbert Yardley revealed all these methods in 1931 in his book The Black Chamber. The book was in response to Henry Stimson shutting down America’s covert signal intelligence gathering capability. Interestingly enough, there wasn’t a CIA when any of this was printed his book or these documents were produced.

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