Developing recipes for invisible ink is the task of
scientists. Putting it to use is generally the work of spies
and others in pursuit of nefarious deeds. It's the work of
the sleuth to figure it all out, at least that's the way
most good mystery novels work! But invisible ink has also
had its place in history.
Artifacts from World
War II turn up quite frequently, but a certain postcard
turned up a few years ago which caught everyone's interest.
The postcard had been sent out of Poland during the
occupation. There wasn't anything of interest to the Germans
on the postcard, or so they thought.