Fill a Used Print Cartridge with Invisible Ink

If you’ve got a spare printer ink cartridge and a document you only want one person to see—or just some free time and a cloak-and-dagger kick—one helpful Metacafe post has a project for you. The tutorial requires a utility knife, some invisible ink pens and a syringe, and an empty ink cartridge, with black seeming to be an easier solution that the yellow-only solution the creator recommends. It’s a fun way to cover up sensitive documents, and a guaranteed friend impresser as well.