It also kept the suits happy. Live album At Folsom Prison (1968) pushed Cash's career into the mainstream, making him the first country music artist to garner the kind of mass media attention usually reserved for pop acts.
Cash peppers his Folsom Prison set with humorous asides and knowing winks in the direction of his captive audience, all too aware that he could rile them to breaking point either by design or by accident.
His songs of love, lawlessness, injustice and redemption are intended to both pacify their souls and tease out feelings of solidarity, providing a safety valve through which their excitement can escape.
Backed by wife-to-be June Carter, Carl Perkins and the Tennessee Three, Cash's delivery is rough and ready. His rich baritone is flawed, breaking up often as he battles with a scratchy throat. But he turns it to his advantage, quipping when a drink of water is supplied: "You serve everything in tin cups?".
It's easy to picture the nervous glances that must have passed between prison authorities as each mention of murder, violence and crime is greeted with a unified hoot of approval.
In any other place the response would seem bizarre; here the fervour evoked by Folsom Prison Blues, Cocaine Blues and condemned man's countdown 25 Minutes To Go is oddly heart-warming and appropriate.
Even break-up song I Still Miss Someone and coal-mining ballad Dark As The Dungeon take on added meaning to the Folsom faithful.
Cash is their spokesman, voicing real-life concerns where they cannot.
When the Man in Black closes his performance with Greystone Chapel, written by Folsom inmate Glenn Sherley, the bond between performer and audience is forever forged tight.
