Forget about waveshapes - it's all about induction. If you have a current flow through a conductor that's adjacent to another conductor, a current flow will be induced into the quiescent conductor. I don't care if the waveshape spells your name; it makes no difference. It's all about flux density, conductivity and proximity.
As for Bill Lawrence's hard-on for aluminum, that's just a pet theory of his with no basis in fact. I don't know why he's fixated on the stuff, but there's no harm in it. At the signal levels and frequencies where guitars operate, and the interference guitar amplifiers are sensitive to, the relative conductivity of the shielding is of little or no consequence past a certain point. It simply needs to be there and it'll be effective.
Faraday cages only work if there are no holes in them larger than the wavelength of the signal you're trying to block. So, right off the bat you're doomed to failure. You gotta cut holes for the pickups, right? Besides, the biggest and most sensitive part of a guitar's wiring IS the pickup, which is necessarily is outside the cage should you decide to build one. So, you're wasting your time. The cage has huge holes in it, and there are antennae sticking out that are connected to very high impedance amplifier inputs. This has failure written all over it if your object is to ignore external signals, and that's been proven 78 bajillion times. Why does anybody suppose Fender and Gibson don't do the insane shielding that some private builders do? Do they think the biggest, richest, highest-priced guitar manufacturers just want to piss off their clientele? Don't be silly. It's not a money thing. They just know better. Most engineers worth their salt do.
That's not to say shielding is unimportant or ineffective. But, it has to be done properly. It's impossible to do completely on a guitar, but it can be taken to a very effective degree by simply shielding the signal wiring itself, or using a common-mode rejection pickup system. Seth Lover of Gibson fame came up with what he called the "humbucker", which does this. Even got a patent on the idea, even though it was nothing new. It was simply a new application of an old discovery. Many pickups since then do the same thing. different packaging schemes produce different sonic results, but the basic concept is the same: reject the common signal through cancellation and keep the differential. Works like a champ.
