For an excerpt from Scientific American: How Chemists Revealed WW I Secret Writing:

see http://www.scientificamerican.com/article/invisible-ink-history-wwi

This book grew out of my discovery of a top-secret invisible ink formula and method. Never before in the history of espionage had any government spy agency released or published a classified secret-writing formula and method.

It was the summer of 2006, and I was in Berlin… I had been submitting request after request to the Stasi archives…..but despite frequent pleas, no secret formula or method for creating an effective secret ink had surfaced from the miles and miles of Stasi files. It was frustrating and disappointing. I was ready to give up.

Then on that summer day, the archivist handed me a thin file hidden underneath a pile of useless files. When I peered inside my mouth dropped open. Right before my eyes I saw a document stamped with the German equivalent of “Top Secret,” and it had a formula written on the first page. I felt like a kid who had just stolen a candy bar. My face flushed. I felt alive and awake… As I leapt two steps at a time down the wooden stairs, I could hear my footsteps echo (or were they someone else’s?) in the cavernous hall. I waltzed out of the building, looked behind me, saw no one chasing me, and fled the building. I finally had gotten what I was looking for.

By this time I was wondering what else had been written about the subject of secret writing in its hidden or invisible form. The answer was: precious little. While bookshelves groaned under the weight of books on cryptography, the study of codes and ciphers, little had been written about its sister discipline, the history of hidden or covered writing, invisible ink, or the art of secret writing… I spent most of the lecture producing simple demonstrations like the classic childhood lemon juice and heat experiment. At that point, I never imagined the rich stories I would find after digging into the dustbin of history.

My curiosity was piqued by the challenge of the hidden history. But it wasn’t until years later, after I had completed Seduced by Secrets… that I decided to tackle this fascinating but hard-to-track history…

The main question animating my quest was: how important was invisible ink? In answering this question I was aided by the fact that British, American, and German archives had recently declassified or released exciting new material about spies and invisible ink from the two world wars and the Cold War that underscored its significance to spy agencies.

This book grew out of that discovery during a summer research trip to Berlin, was researched out of curiosity, and was written because of a need. It is the volume I wish I had found on the shelf.