If Black Sabbath hadn't done a farewell tour, we might have gotten a surprising dose of the blues from the masters of metal.
Geezer Butler told Music Radar that "The follow-up to 13 was going to be a blues album, but the tour got in the way. It would take something like two or three years to do it properly, and we thought we might not all be here by that time, so it would be better to do this final tour first and then maybe we'll do a blues record later."
When the interviewer suggested that doing a blues album in a "jam style" would make it easy for them to record quickly, Butler agreed and added, "You'd have to make it varied instead of doing ten tracks of the same old 12-bar blues, though. But even back in the Heaven And Hell tour days, Tony would go up into his lead and we would just jam around blues riffs for eight or nine minutes. And every night was different. So that is a thought."