WASHINGTON — The CIA lifted the lid on one corner of the cloak and dagger world of World War I, declassifying six of the oldest secret documents in the U.S. government archives, the agency announced yesterday.
The documents show top techniques used by spies, generals and diplomats to send secret messages in a diplomatic war that raged long after the guns stopped. The records reveal how invisible ink was used to send word between allies, and how spies learned to open letters to read each other's secrets without leaving a trace.
One document suggests this method for passing secret messages: soaking a handkerchief or collar in a mixture of nitrate, soda and starch, then drying the fabric. The chemicals come out when the cloth is placed in water. The liquid becomes invisible ink that can be loaded into a pen and used to write a message. The recipient develops the writing by applying a second chemical, iodate of potassium.
There's even a document written in French of the Germans' secret ink formula, showing the French had cracked the enemy's code.
"These documents remained classified for nearly a century until recent advancements in technology made it possible to release them," CIA ...