Fountain Pens - CIA declassifies their invisible ink recipes

For the fountain pen users out there the CIA list a number of declassified documents including their invisible ink recipes.

https://www.cia.gov/library/readingroom/...et-writing

One of the documents talks about a couple recipes that use acids and notes this would be rough on steel pens so they recommend a quill.

Okay, that is too fascinating and too weird, all at the same time. I think I'll stick with Diamine.

If you want to read my response just hold your laptop over a flame

I did and all I got was a funny smell. What was the message supposed to say?

This may also explain the invisible ink feature in the iPhone's text messaging app in the latest iOS update