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CIA Recipe For Invisible Ink Among Newly Released Wwi-Era Documents

By The Washington Post
April 20, 2011
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So you want to open sealed envelopes without getting caught? Here’s the secret, according to one of the six oldest classified documents in possession of the Central Intelligence Agency: "Mix 5 drams copper acetol arsenate. 3 ounces acetone and add 1 pint amyl alcohol (fusil-oil). Heat in water bath—steam rising will dissolve the sealing material of its mucilage, wax or oil."

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