Ozzy Osbourne backstage at the 1974 California Jam
Frank Zappa gave “Supernaut,” the ur-metal monster that ends the first side of Black Sabbath Vol. 4, the number one spot in his list of “faves, raves, and composers in their graves,” published in the June 1975 issue of Let It Rock:
‘Supernaut’: Black Sabbath. I think it’s from Paranoid. I like it because I think it’s prototypical of a certain musical style, and I think it’s well done. Also, I happen to like the guitar lick that’s being played in the background.
Eventually, Neil Slaven’s Zappa biography Electric Don Quixote reports, “Iron Man”—the Sabbath song Zappa chose to play in his DJ set on BBC Radio One in 1980—replaced “Supernaut” in the maestro’s affections:
A couple of years later, he’d changed his mind. He told Hugh Fielder, “‘Iron Man’. Are you kidding me? ‘Iron Man’! That’s a work of art. I used to like ‘Supernaut’ but I think ‘Iron Man’ is the one now.”
But in the mid-70s, it was strictly “Supernaut,” and the Sabs benefited from Zappa’s enthusiasm. Sabbath bassist and lyricist Geezer Butler, a Zappa fanatic who says his “musical life completely changed” when he first heard the Mothers of Invention at the age of fifteen, credits Zappa’s endorsement of “Supernaut” with changing critics’ attitudes toward the band:
I think some of them got an inkling when Frank Zappa did this interview in one of the big English music papers. They were asking him what music he was listening to at the time, and he said, “Black Sabbath.” And at the time, Frank Zappa was really well thought of critically. And I thought he was joking! (Laughs.) But he thought “Supernaut” [from 1972’s Black Sabbath, Vol. 4] was the best riff he’d ever heard. And a lot of critics went, “Well, if Zappa likes Black Sabbath, maybe we should give them another listen.”
Frank Zappa talking to Let It Rock magazine, 1975
On the strength of “Supernaut,” Zappa invited Black Sabbath to dinner, a Rashomon-like encounter that Ozzy and Tony Iommi recall differently in their memoirs. Everyone seems to agree that there was a party in an American city around 1974. Ozzy gives the short version of the story in Barney Hoskyns’ Into the Void:
Frank Zappa – who was a very techno guy – invited us to a restaurant once where he was having a party. He said, ‘The song “Supernaut” is my favourite track of all time.’ I couldn’t believe it – I thought, ‘This guy’s taking the piss: there’s got to be a camera here somewhere…’
The singer expanded on these remarks in I Am Ozzy, adding a lot of colorful detail:
Another crazy thing that happened around that time  was getting to know Frank Zappa in Chicago. We were doing a gig there, and it turned out that he was staying at our hotel. All of us looked up to Zappa – especially Geezer – because he seemed like he was from another planet. At the time he’d just released this quadraphonic album called Apostrophe (’), which had a track on it called ‘Don’t Eat the Yellow Snow.’ Fucking classic.
Anyway, so there we were at this hotel, and we ended up hanging out with his band in the bar. Then the next day we got word that Frank wanted us to come to his Independence Day party, which was going to be held that night at a restaurant around the corner.
We could hardly wait.
So come eight o’clock, off we went to meet Frank. When we arrived at the restaurant, there he was, sitting at this massive table, surrounded by his band. We introduced ourselves, then we all started to get pissed. But it was really weird, because the guys in his band kept coming up to me and saying, ‘You got any blow? Don’t tell Frank I asked you. He’s straight. Hates that stuff. But have you got any? Just a toot, to keep me going.’
I didn’t want to get involved, so I just went, ‘Nah,’ even though I had a big bag of the stuff in my pocket.
Later, after we’d finished eating, I was sitting next to Frank when two waiters burst out of the kitchen, wheeling a massive cake in front of them. The whole restaurant went quiet. You should have seen that cake, man. It was made into the shape of a naked chick with two big, icing-covered tits – and her legs were spread wide apart. But the craziest thing about it was that they’d rigged up a little pump, so champagne was squirting out of her vagina. You could have heard a pin drop in that place until the band finally started to sing ‘America the Beautiful’. Then everyone had to have a ceremonial drink of the champagne, starting with Frank.
When it was my turn, I took a long gulp, screwed up my face, and said, ‘Ugh, tastes like piss.’
Everyone thought that was hilarious.
Then Frank leaned over and whispered in my ear, ‘Got any blow? It’s not for me – it’s for my bodyguard.’
‘Are you serious?’ I asked him.
‘Sure. But don’t tell the band. They’re straight.’
In Iron Man: My Journey through Heaven and Hell with Black Sabbath, Iommi records different memories of the first meeting with Zappa, including which song he singled out for praise. In his account, Iommi rushes through the dinner to get to the 1976 Madison Square Garden show where Zappa had planned to play with Sabbath:
We had met Frank Zappa at a party in New York a couple of years before. He took us all out to a restaurant, telling us how much he liked ‘Snowblind’. It was very kind of him and we became friends. On 6 December  we played Madison Square Garden, with Frank introducing the band. He wanted to play as well. We’d put his stuff on stage but we had a really bad night. Frank was waiting to walk on and I thought, he can’t, it’s disastrous, everything is going wrong, my guitar is going out of tune, there’s noise and crackles and God knows what. So I said to him: ‘It would be best if you don’t play, really.’
Zappa, for his part, said that he had been prepared to play with Sabbath but declined because he didn’t get a soundcheck. Instead, he “introduced them and then sat by the side of the stage over by Ozzy’s orange juice.” (You can hear almost unintelligible audio of Zappa introducing “the rocking teenage combo known to the universe as Black Sabbath” on YouTube.) But this missed opportunity was not the final musical meeting between FZ and the Sabs. Iommi:
When I went to see [Zappa] once in Birmingham, he said: ‘I’ve got a surprise for you tonight.’
They played ‘Iron Man’. I was in the bar and I heard them play it and I thought, bloody hell! I went back out and I thought, I’ll thank him after the show. But he had such a bad night that he stormed off stage, really pissed off. So I thought, hmm, I don’t think I’m going to go back. Even so, it was a nice surprise.
It was announced this very morning that Frank Zappa’s Roxy: The Movie, which fans have waited patiently to see for decades, is finally getting released on DVD & Blu-Ray on October 30th by Eagle Rock Entertainment and the Zappa Family Trust.
Below, hear Sabbath’s outstanding 1975 set from Asbury Park, NJ. “Supernaut” begins at the 1:00:30 mark, followed immediately by “Iron Man.”