Black Sabbath's 1970 self-titled debut was like nothing anyone had ever heard before, and their sophomore work Paranoid only expedited their popularity. By 1971, almost every band was creating heavy music, but Sabbath proved they still did it best when they released Master of Reality. 

Ozzy Osbourne, Tony Iommi, Geezer Butler and Bill Ward recruited producer Rodger Bain for one final time to work on the record. The 32-minute set opens with Iommi coughing up a storm in the studio after smoking a joint during "Sweet Leaf," thus it has been hailed the pioneering album of genres like doom and stoner metal.

Released on July 21, 1971, Master of Reality has since been certified 2x platinum by the RIAA, and for good reason. Here are eight facts you may not have already known about it.

1. They spent more time working on it than its predecessors. 

Ward recalled to Metal Hammer that the band were able to take more time to work on Master of Reality than they did for Black Sabbath and Paranoid. “On the first album, we had two days to do everything, and not much more time for Paranoid," he said.

"But now we could take our time, and try out different things. We all embraced the opportunity: Tony threw in classical guitar parts, Geezer’s bass was virtually doubled in power, I went for bigger bass drums, also experimenting with overdubs. And Ozzy was so much better."

2. They tuned things down.

To ease the pain after suffering a factory accident that severed his fingertips, Iommi downtuned his guitar. Butler followed suit in order to match the sound, which was sludgier and heavier than heard on their prior albums. This would pave the wave for the sound of later bands like Alice in Chains and Soundgarden, who used drop-d tuning for their own songs and cited Led Zeppelin and Black Sabbath as the influencers of that decision.

3. Ozzy Osbourne struggled while recording "Into the Void."

Butler had the lyrics written out for Osbourne when it came time to record the vocals, and Iommi recalled the singer struggling with them a bit. "It has this slow bit, but then the riff where Osbourne comes in is very fast. Osbourne had to sing really rapidly: 'Rocket engines burning fuel so fast, up into the night sky they blast,' quick words like that," he wrote in his autobiography Iron Man: My Journey Through Heaven and Hell with Black Sabbath.

"Seeing him try was hilarious," the guitarist added. Listen to an isolated vocal-version of the song below — the words start at the 1:43 timestamp.

4. Sweet Aftons and "Sweet Leaf."

"Sweet Leaf" is an obvious ode to marijuana. The name for the song, however, was inspired by an Irish brand of cigarettes called Sweet Aftons.

"I'd just come back from Dublin, and they'd had these cigarettes called Sweet Afton, which you could get only in Ireland," Butler once told Guitar World. "We were going, 'What could we write about?' I took out this cigarette packet, and as you open it, it's got on the lid, 'The Sweetest Leaf You Can Buy!' And I was like, 'Ah, Sweet Leaf!'"

Science & Society Picture Library, Getty Images

5. Masters of misprints.

The earliest U.S. editions of the album featured a misprint in the album title, which read Masters of Reality. In addition, it read that there were 11 songs as opposed to eight, adding "The Haunting," "Step Up" and "Deathmask" as part of the track listing.

6. Iommi showcased his many talents.

The guitarist brought more to the table on this album than sick riffs. On the song "Solitude" in particular, he also played the flute and the piano.

7. "After Forever" showed a different side of the band.

Black Sabbath were known for being dark, and were accused of being Satanists in their early years. The lyrics for "After Forever" were written by Butler about Christianity, having been brought up in a Catholic home.

"It was just a bad time in Northern Ireland, setting bombs off in England and such," Butler told the Weeklings of what inspired him to write the song. "We all believed in Jesus — and yet people were killing each other over it. To me, it was just ridiculous. I thought that if God could see us killing each other in his name, he'd be disgusted."

8. It was one of their only albums to chart in the Top 10 in the U.S.

Master of Reality was Sabbath's first album to crack the Top 10 in the U.S. according to their Billboard chart history, and the only one until 13 came along over 40 years later.

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