The art of filing
If you want to play a concertina with other instruments, it needs to be in modern concert pitch (A=440Hz). Since most concertinas were made before this pitch was internationally agreed, any unrestored instrument will need to be retuned.
This is done by gently filing the reeds, at the tip to sharpen the note, and near the root to flatten it. Simple, yes? Well, no. It's easy enough to remove metal from the reed, but much harder to put it back! You also have to take into account the clearances, and the 'set' of the reed (the height at which it sits above the frame). Get it right, and the instrument should respond fast and evenly, right across