Add Yahoo as a preferred source to see more of our stories on Google. William Abel, a mail censor at Iowa's State Prison, Fort Madison, using a hot iron to bring out a secret message written in lemon ...

A Hillhouse student’s eyes widened as he applied grape juice and heat to what appeared to be a blank piece of paper — but instead held a secret message in invisible ink, written as part of a course ...

Prisoners, Lovers, & Spies is the first history of invisible ink and secret communications revealed through thrilling stories about scoundrels and heroes and their ingenious methods for concealing ...

Which invisible ink pens are best? Spies and conspirators have used invisible inks for millennia to send messages. In the modern age, invisible ink pens are an excellent way for grown-ups to ...

Hillhouse students at work writing invisible ink messages … … after their teacher, Kate Goodwin, applies heat to reveal invisible messages in class about the ...

Which invisible ink pens are best? Spies and conspirators have used invisible inks for millennia to send messages. In the modern age, invisible ink pens are an excellent way for grown-ups to ...