On November 29th, 1775 invisible ink was created! Sir James Jay (related to one of our founding fathers, John Jay) had created what they called "sympathetic stain" or "white ink" to help the Patriots communicate with one another secretly. There were two solutions involved in "white ink", one to write the message and the second to recover the message. In 1779, George Washington used Sir James Jay's invisible ink to communicate with Colonel Benjamin Tallmadge.
I can't wait to use some in my spy notes!