A Closer Look at Invisible Inks

What do Edgar Allen Poe, George Washington, and Benedict Arnold have in common? They all employed various sympathetic stains (invisible inks) to safeguard their communications. 

In constructing secret messages, each author was careful to create a visible “cover letter” – usually having ample room between written lines to hide a “secret message”. Later, the invisible ink line(s) were applied between the visible ones. The recipient later applied a “developer” to read the secret message.

Invisible ink chemistry involves the application of a colorless substance (the invisible ink) to paper (usually) and allowed to dry. Subsequent application of a specific developer – such as copperas (antiquated term for copper sulfate) – over the “invisible” area(s) of the message allowed the invisible message to become visible! 

  • Download this PDF to learn how to create and develop secret messages using invisible inks.