By . Mark Duell . Last updated at 9:00 AM on 13th July 2011 . This fascinating document containing a Harry Potter-style secret formula for invisible ink was one of the oldest still classified by the U.S. Now newly-declassified material, including the details on German secret ink formulas dating back to World War One, has been put on show to the public in Washington D.C. The National Archives is showcasing the series after a 95-year period of secrecy and a 1918 document shows the ink was made by mixing compressed or powdered aspirin with pure water. Fascinating release: The German invisible ink formula, written in French and translated, is described in an Office of Naval Intelligence document dated June 1918 . The invisible ink formula, written in French and translated, is described in an Office of Naval Intelligence document. This shows that the French managed to crack the German's formula, reported CBS News. Invisible ink was used by allies and spies during World War One to communicate safely by sending secret messages. The 1918 documents, which went on display this week and will remain on view through the end of July, were released by the archives as part of an open government initiative. They were made public by the National Archives National Declassification Center along with the Central Intelligence Agency. Formula: The German invisible ink was made by mixing compressed or powdered aspirin with pure water . The documents were thought to be the oldest still classified by the U.S. before they were released. The National Declassification Center in Maryland launched in December 2009 to review more than 400 million pages of classified records by the end of December 2013. The CIA explained in April why the documents were not released to the public for such a long time. 'These documents remained classified for nearly a century until recent advancements in technology made it possible to release them,' CIA Director Leon E. Panetta said at the time.
Series of declassified documents go on show to public at National Archives .
Document from June 1918 shows aspirin and water were mixed to create ink .
It is written in French and shows how they cracked German ink code .
By . Mark Duell . Last updated at 9:00 AM on 13th July 2011 . This fascinating document containing a Harry Potter-style secret formula for invisible ink was one of the oldest still classified by the U.S. Now newly-declassified material, including the details on German secret ink formulas dating back to World War One, has been put on show to the public in Washington D.C. The National Archives is showcasing the series after a 95-year period of secrecy and a 1918 document shows the ink was made by mixing compressed or powdered aspirin with pure water. Fascinating release: The German invisible ink formula, written in French and translated, is described in an Office of Naval Intelligence document dated June 1918 . The invisible ink formula, written in French and translated, is described in an Office of Naval Intelligence document. This shows that the French managed to crack the German's formula, reported CBS News. Invisible ink was used by allies and spies during World War One to communicate safely by sending secret messages. The 1918 documents, which went on display this week and will remain on view through the end of July, were released by the archives as part of an open government initiative. They were made public by the National Archives National Declassification Center along with the Central Intelligence Agency. Formula: The German invisible ink was made by mixing compressed or powdered aspirin with pure water . The documents were thought to be the oldest still classified by the U.S. before they were released. The National Declassification Center in Maryland launched in December 2009 to review more than 400 million pages of classified records by the end of December 2013. The CIA explained in April why the documents were not released to the public for such a long time. 'These documents remained classified for nearly a century until recent advancements in technology made it possible to release them,' CIA Director Leon E. Panetta said at the time.
back to World War One, has been put on show to German invisible ink formula, written in French Naval Intelligence document dated June 1918 . The invisible ink formula, written in French and Archives National Declassification Center along documents were not released to the public for