Black Sabbath’s Tony Iommi and Geezer Butler were interviewed by Guitar World for their March issue. During the chat, the guys talked about their legendary 1970 self-titled debut. Many credit the band, and that disc specifically, as defining the heavy metal genre. The guys recorded their debut disc in one day, in one session, a fact that has become part of rock legend. But it turns out, there is more to the story.

The band actually had two days booked in the studio to record the album, but only used one. Butler told Guitar World magazine, “We had two days to do it, but we didn’t know any better.” He continued, “We just went in there and recorded it like a live gig.” So why'd they cut the session short? Butler went on to say they nixed the second day and even bailed on the mixing for the disc because they had to get on the road to play a show.

That same year, the band recorded their second record, ‘Paranoid,’ following a similar formula. This time taking a few days to cut the disc, which birthed some of Sabbath’s most successful songs, ‘Paranoid,’ ‘Iron Man,’ and 'War Pigs.'

‘Black Sabbath’ was released on Friday the 13th in 1970, and the band and fans alike will celebrate it’s 45th anniversary on the same date this month, which also happens to fall on a Friday. Check out more from the Guitar World interview here.