It is a classic rite of passage for nerdy kids to write secret messages using lemon juice. If you somehow missed that, you can’t see the writing until you heat the paper up with, say, an old-fashioned ...

Invisible ink is back, and it’s better at hiding than ever. A new invisible ink that you can print is harder to reveal than most common cyphers. Liang Li at Shanghai Jiao Tong University in China and ...

I think everyone is aware of the trick with invisible ink. Write your message in lemon juice on paper, and when the juice dries it cannot be seen. But if you heat the paper, the lemon juice reacts ...