woodworkingboy
TreeHouser
Have used kerosene and a stiff nylon brush. On really tough crud I have also put them on top of the wood stove for a bit and the heat loosened it up even more. Even put one inside the stove once. I suspect that you could take a torch and do similar, being careful not to get it so hot that it compromises the cutting edges. I like to stick one in an oil bath after that, so I keep a big mouth jar full of oil for that purpose, then hang the chain up and let it drip back into the jar.