Have you ever wanted to make really good invisible ink? Well, the Central Intelligence Agency has a reliable recipe it’s now happy to share. As part of a large declassification of the U.S. government’s six oldest classified documents, the CIA has made publicly available a number of tips sure to amaze your six-year-old nephew, like how to make invisible ink and how to open envelopes without breaking the seal.

Many D.C. residents have had something stolen from them at one point or another. But did you know that the Metropolitan Police Department participates in an initiative called “Operation ID,” which can help you get your possessions back? It’s a simple system: MPD will give you a free ultraviolet pen, which you then use to mark your stuff with something identifiable, like your last name and driver’s license number. When the cops make a bust, they’ll scan the recovered goods — officers are trained to look in certain areas depending on the item — and, if there’s a notation, they’ll be able to reunite you with your belongings. It’s hardly a perfect system (the ink can smudge and criminals probably can get their hands on a black light with ease), but hey, something’s better than nothing, right?