Last week I told everyone how I created my own invisible ink from household items like lemon juice, honey water, etc. A super-fun experiment, I gotta say. Of course, then I learned that those heat-developed inks were seldom used by the 18th century because they were so easy to develop. Anyone could just hold any letter to a flame and see if a message appeared. I can still use it in my story for not-crucial correspondence, but the actual letters of espionage to General Washington during the war used something very different.

Something called “the sympathetic stain.” Historians still don’t know exactly what it was, though they have a pretty good guess, based on the clues left to us as to where they had to procure the ingredients. Interestingly, it was John Jay and his brother who came up with this stain–and the first time it was used was when said brother wrote a letter of warning from England when that nation was gearing up for war.

The awesome thing about this stain is that is can be developed only by a very particular reagent, which only the folks corresponding regularly had in their possession. You couldn’t just stumble upon it. And because of that, letters written in the stain were very secure.

And the stain was very precious. So precious, in fact, that a few of the folks in possession of it were afraid of running out and so did not use it on some key correspondence–and got wrist-slapped by Washington for it, LOL.

The stain was nonetheless difficult to use. You needed high quality paper for it to work well on, and just the right amount of reagent to develop it. Too much would wash away the ink, too little just wouldn’t make it reveal. Apparently they took to using a paint brush to apply it.

The code name for this stain was “medicine,” and the Jays shipped it to Washington in a medical supply box. Had anyone intercepted it, it would have looked like any other vial of liquid medication.

But it wasn’t. It was the agent that allowed key information to pass to the Patriot army. Information that may have saved us from becoming British colonists again.

Hooray for the Sympathetic Stain! =)

On a side note, check out my guest blog on F.A.I.T.H. Girls today, on the topic of being one of many wives in a harem.