How Many Ways Can Vintage Pickups Become Demagnatized Over Time?

1) Natural decay. I'm not sure how much of a factor this is but if it exist it is unstoppable.

 Being exposed to an opposite magnetic field for a prolonged period of time. This could happen in any number of ways;

2) like on an electric train near powerful electro magnetic motors,

3) having someone drill or dremel on your guitar with the pickups in,

4) being near a power generator,

5) being stacked or stored with other pickups with opposite polarity,

6) getting banged directly like with a whammy bar or something metal

7) being stored near an electric fan or other motorized device that runs constantly and produces an electro magnetic field.

8) having your wife vacuum around your guitar collection regularly.

9) keeping your guitar or pickups near a speaker with a powerful magnetic field.

Why is this important? well maybe natural loss of some magnetism over time is part of that vintage sound. If your pickup magnets become totally demagnetized the pickups will not work. I've seen a set of Stratocaster pickups, where the middle was reverse wound reverse magnetic polarity, actually have the middle pickup switch polarity because of being stored between the other two pickups sandwich style. So the moral of the story is; If you like the way your pickups sound, be wary of having your guitar or pickups in the presence of powerful magnetic fields for any length of time.