In 1775, Sir James Jay invented invisible ink.
During the United States Revolutionary War, George Washington wanted a way to pass messages without the British reading them. While other ways of secret messages existed, Washinton wanted something new. The British knew these other ways too.
Sir James Jay was the brother of an American Patriot and a chemist. Hearing the call, he decided to experiment. Eventually, he created invisible ink. Sir Jay’s brother passed the chemical onto Washington, who passed it on to his chief spy. He instructed them to write private letters between lines of banal information or on the blank pages of cheap pamphlets.
While we don’t know how helpful this invisible ink was to the defeat of the British, knowing Washington used it is fun. It shows how something we might consider a toy was once useful for a revolution.