Originally Posted by Jens Nordlunde
Somewhere I read that the magnetism of the Earth was so weak that it would make little or no influence on a sword, although it was lying for a long time in the same place.
Do you have any comments to this. If you do, please come with themJ.
That's why I wrote "however it's even a big question if this _ever_ happens". In general I would say that magnetic field of the earth is strong enough to magnetize all the ancient pottery. It's way more tricky with swords and big iron objects in general. I'm pretty sure that in a cool place 5000-10000 years of lying in the same place will certainly make a difference, and may be it will make a lot of difference if the sword is heated up and sloooowly cooled down.
In short there are so many parameters (defects in the crystalline structure, historical facts like being made in the place with iron deposits, macroscopic shape etc.) that can affect any sword's magnetization that it's impossible to guess "why ?".