When I was a kid, I could write in invisible ink – really! Take some lemon juice, apply to paper with a brush or stick, and then heat over the light bulb in one of our living room lamps. Voila! Brown lettering would appear on a blank white sheet of paper. A bit unsophisticated perhaps, but it worked. I didn’t really have any secrets to smuggle past the authorities – it was the mere fact of writing invisibly that made it so cool.
Now here I am, all of these years later, still fascinated. A recent news item from the Central Intelligence Agency caught my eye – “CIA Declassifies Oldest Documents in U.S. Government Collection.” The subject of these mysterious papers, which date back to 1917 and 1918: invisible inks! I had to check it out.
The CIA describes these timeworn items succinctly and well: “One document outlines the chemicals and techniques necessary for developing certain types of secret writing ink and a method for opening sealed letters without detection. Another memorandum dated June 14, 1918 – written in French – reveals the formula used for German secret ink.” My favorite is document number 6: Invisible Photography and Writing, Sympathetic Ink, Etc., a four-page pamphlet compiled by Theodore Kytka, identified as “Handwriting Expert, San Francisco, Cal.” and “printed by the San Francisco Division [of what, I wonder? It doesn’t say] for the information of Post Office Inspectors.”
According to the CIA, only recently have advances in technology made these various formulae obsolete, spy-wise. Among the secrets: “A German Formula. Take one ounce of alum and one ounce of white garlic juice. Write with a quill and on heating the paper the letters become very legible and cannot be removed by salt water application.” Then there’s “Disappearing Ink. Take a weak solution of starch, tinged with a little tincture of iodine. The bluish writing will soon fade away.” Boy, is my mother lucky I didn’t latch onto this information – our kitchen would have been a disaster area!
Not only is this a really great story, it also ties into GPO’s 150th anniversary in a very interesting way. During World War II, our scientists helped to thwart the use of invisible inks, like those described above, by Axis prisoners of war. In my next post, I’ll tell that story. Stay tuned!