An American Songwriter piece looks at three iconic rock guitar tones from the 1970s that were born not from careful design but from accidents and improvisation. It highlights how limitations and mishaps forced guitarists Tony Iommi, Eddie Van Halen and Mike Campbell to innovate, ultimately producing sounds that defined their bands and influenced generations of musicians.

Tony Iommi lost his fingertips in a factory accident aged 17 and fashioned thimbles from a melted plastic bottle while loosening his strings, inadvertently creating the downtuned, heavy sound that helped found heavy metal with Black Sabbath. Eddie Van Halen's famed "brown sound" emerged from trial-and-error tinkering with cheap parts, modified amps and lowered voltage rather than a deliberate plan. Meanwhile, Mike Campbell of Tom Petty and the Heartbreakers improvised a makeshift 12-string effect on "American Girl" by layering droning guitar notes with Petty's rhythm part, a workaround that became a signature element of their sound.