WWII Spycraft: Invisible Ink

[Scroll over the image for details.]   "Give me the secret ink von Karsthoff gave you," Abwehr agent Johann Jebsen said to Dusko Popov in Rome on November 21, 1940.  Popov did and watched as Johnny poured it out.  "We have a new and better formula," Jebsen said, "with pyramidon." Dusko listened carefully as Johnny explained how to prepare the concoction, memorizing the ingredients and application (see Chapter 4 of INTO THE LION'S MOUTH for the precise formula).  Over the next four and a half