Sand off the blue with some 320 or 400 grit wet or dry sandpaper. Degrease it with acetone. At that point you can maybe use Plum Brown and a torch. It works well for small parts. Depending on the color you may want to use a commercial rust brown like Danglers or Laurel Mtn. Forge. They need some humidity to work and small parts like your tang can be suspended in a can with some water in it.