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Documents Uncover Invisible Ink Formula

By Marcella Glenn

Newly declassified, nearly century old CIA documents, typed and hand-written with titles like "Secret Writing", among other things, show formulas for making and uncovering invisible ink.

The six papers date as far back as 1917, and before their release on Tuesday were among the United States' oldest classified documents.

One of them exposes the ingredients used in German secret ink. The documents indicate early 20th century spy methods.

"These documents remained classified for nearly a century until recent advancements in technology made it possible to release them," CIA Director Leon Panetta explained in a statement. "When historical information is no longer sensitive, we take seriously our responsibility to share it with the American people."

A related document in English tells spies how to expose the German correspondence, "examine through powerful beam of light directed on surface at different angles."

The instructions continue with spy novel type techniques, including dusting a little powdered charcoal over the paper's surface.

"Run a hot iron over the surface being careful not to scorch the paper," per the instructions. "Wet with water."

One of the CIA documents listed instructions on how to open a sealed letter without detection.

"Heat in water bath - Steam rising will dissolve the sealing material of its mucilage, wax, or oil," the instructions read. "Do not inhale." Mucilage is a type of glue.

Originals live at: The National Archives and copies are available on the CIA's web site http://www.foia.cia.gov/.