Remember back in the days when you were a kid, and writing down secret messages to one another involved using lemon juice? Of course, this was the most basic of all kinds of invisible ink, but didn’t that tickle your imagination all those years ago? Here is a project that you might want to consider for your coming weekend – that is, to make good use of an old printer by replacing the ink in a color inkjet cartridge with concentrated lemon juice – letting you print with invisible ink, of course. In the event where you want to read a received secret message, just spray or wipe the paper with iodine tincture and you’re good to go. Of course, there is also the option of heating up the paper with a hot iron just in case you do not have any iodine handy. Your household will probably wonder why you’re printing out nothing through the printer, with this weird smile on your face all the time.