…absent any obvious exposure to existing permanent magnets or magnetic fields?
For example, I have this square glass container with a metal lining on the bottom, in which I keep mainly coins, guitar picks, and other objects. Some are metal and some aren’t.
Picture
(You may need to rotate it a quarter-turn to the right.)
Originally this object was a decorative candle which, when used for its original purpose, would have been placed on a table upside down with respect to this shot. I’m not sure what kind of metal that is, but it’s obviously become highly magnetic. Notice that the penknife sticks not to the container itself, but to a steel screw which, in turn, sticks to the container. To remove these objects requires a significant tug, by no means is it the case that they’re barely hanging on.
I usually have this in my medicine cabinet whose shelves are just wide enough hold it, the idea being that when getting ready to to go out I can grab a few coins if I think I’ll need to feed a meter or tip a barista. I only mention the medicine cabinet because that’s obviously metal as well.
I’ve also noticed that herb grinders become magnetic, especially at the center of rotation.
What gives? I know that under certain conditions a piece of metal can be imbued with a permanent magnetic field by being rubbed or struck a certain way with another metal object, and that will happen with the herb grinder, as the top part is twisted over the stationary base. But how did my glass and metal box become so strongly magnetized?