I know I'm reeeeallly new here, but I do have some experience with magging/demagging. I spent 15 years in industries that relied on magnetic materials and mag/demag processes.
For tools like chisels with small tips, the process of sharpening or even honing can be enough heat to cause a small magnetic charge. Impact, like when I pound on my screwdivers with a framing hammer cause I can't find my chisels, will also cause the electrons to align enough to notice the charge. The small tip also focuses the magnetic field, and causes the chips and shavings to stick exaclty where we don't want them.
Passing the tool through any magnetic field can reverse the charge in tool, if you go through the 'charging' field in the opposite direction to the charge in the tool. If the tool get more magnetic, reverse the direction of travel through the field, or reverse the tool and go though in the same direction. If it still gets stronger, move the tool through the field further away, where the 'charging' field is weaker. Rinse and repeat.