There can be variances in the magnet when rubbing two magnets (or pickups) together and the results will be inconsistent and not very accurate. Magnets can be degaussed (de-magnetized) by several means: They will slowly de-magnetize over a period of time (many years), heat, shock, other external magnetic fields and alternating currents. You will get haphazard results when rubbing pickups together that may be difficult for you to restore or control.

Many years ago I build a magnetic calibrating system I nicknamed the “Dun-Stunner”. It allows me to calibrate Alnico magnets with consistent results. I can duplicate magnetic field strength of desired sounding pickups while matching the D.C. resistance of the coil to restore it back to original specifications. When I calibrate a magnet I call it “Dun-aged”. It’s important when you need to properly duplicate a magnet, when restoring a vintage instrument.