I'm wondering if anyone has experimented with, or has any info on the effect of pickup surrounds with different magnetic properties? The trad tele bridge pickup, and old Valco lap steel pickups got me thinking about this, being surrounded by ferromagnetic steel. OTOH, copper, lead and zinc are diamagnetic, while aluminium is paramagnetic, and these might have different effects on pickup tone. For example, is there any good evidence that using copper shielding on a pickguard affects the tone? How about aluminium? EDIT I might try the experimental approach on this.