Thus was born the idea of the scratch guitar controllers.
I experimented with a bunch of materials trying to find a resistor with the properties I needed, including VHS tape, tin foil, nichrome wire and conductive thread, to name a
few, before I stumbled on conductive foam. The foam is normally used to ship delicate electronics & ICs because it prevents the buildup of static electricity. It costs just a few dollars per sheet. I used the 1/4″ thick variety and paid about $7 for enough to make more than a dozen guitars. Other materials include scrap MDF, old futon slats, empty plastic film canisters (free from any place that still develops film), metallic tape (from any hardware store) & speaker wire.