Mumetal is a high magnetic permeability alloy. It is known any kind of mechanical deformation changes its microstructure leading to loss of superior magnetic properties. Annealing of machined parts fabricated from mumetal is standard. I keep reading in literature, perhaps everyone getting that from the same source, that it is ideal to anneal mu-metal at 1120degC in hydrogen and then have controlled cooling. My question is why hydrogen specifically? What is the scientific reasoning behind this? I am assuming they just want zero oxygen or contaminant environment? Cant this be done just as well in a vacuum furnace or perhaps surface coat the mumetal part in a ceramic coating before heat treatment in moderate oxygen environments? Reduce impurities? Perhaps that could have been done with other steps instead instead?