Turning the childhood invisible ink trick on its head, this mod from Make allows you to print out invisible messages with your inkjet printer.


Matt Richardson put together this excellent video with instructions on how perform this invisible ink mod originally from Make: Volume 16.

Modding your inkjet cartridge to print out concentrated lemon juice, instead of yellow, allows the message to be hidden and only revealed with extreme heat (as from a clothes iron) or iodine. Don't try using lemon juice though - it is not concentrated enough with the inkjet method and you will need something a bit stronger.


How-To For Secret Agents: Invisible Ink Printer Mod via Make.