Someone is confused between button accordions and melodeons!

Button accordions, as played by Jimmy Shand are typically three row or five row chromatic (same note both ways), not diatonic (push-pull) like the melodeon.

The right hand buttons play diagonally in semitones, the three row being more awkward to play in some keys. The five row is really a three row with two of the rows duplicated for ease of playing. The left hand is as piano accordion, excepting that 96 bass is usually the most you'll get (though someone else probably knows differently!).

However, John Kirkpatrick put a spanner in the works by combining a three row melodeon with an accordion bass, so that it became a diatonic button accordion...

Most accordion, melodeon and concertina reeds are steel, only older/cheaper ones have bell metal reeds (like harmonicas). The better quality accordions and melodeons ones have two reeds (push and pull) per reedplate, cheaper ones are made like harmonicas with all the reeds on the same plate (a bugger to repair!).

If you've got an older box with leather valves (the flaps on the reedplates of lower notes), it's worth changing them for the more reliable modern plastic ones. You'll be amazed at how much 'tighter' the box plays - particularly important for melodeons.

My box is a 30 year old Hohner Musette IV 120 bass made in Switzerland, which I've had from new. If anyone wants to hear it, I can send you an mp3 file of a tune - it's an amazingly 'mellow' (what on earth does that really mean?!!) sound...