Formerly classified documents dating back to 1918 have arrived at the National Archives in Washington. Among the century old secrets - a recipe stolen from Germany for disappearing ink.
The documents have been kept secret for 95 years, and were said to be among the oldest still classified in the United States. The secret papers were released on April 19, 2011 by the National Archives National Declassification Center, in coordination with the C.I.A., as part of an open government initiative.
Germany's secret ink formulas from World War I are part of the display. Other documents, written in French, describe how to make invisible ink: powdered aspirin mixed with water, for any apprentice spies taking notes.
The display is free and open to public during Museum hours, 10 a.m. - 7 p.m. until July 31, 2011. It is located in the East Rotunda Gallery of the National Archives Building in Washington DC (Constitution Ave and 7th St, N.W.).