The answer is at the outdoor merchandise tent, where a throng wearing black T-shirts is jostling to buy yet more black tees.

Inside, it's a blur of Motorhead, Iron Maiden, Cannibal Corpse, Danzig and Tumbleweed tees worn by metal heads young and old, round and reedy, bearded and bum-fluffed.

It’s as though an infographic of all the bands influenced by Black Sabbath came to life – then came to the gig.

When the War Pigs siren sounds, most fans are caught out partying by the bar. Any glimpse of the stage I manage during War Pigs’ eight-minute epic is through a tide of latecomers doing the devil horns.

I can hear it, though, and when Ozzy Osbourne starts chanting “Hey! Hey! Hey!” as Tony Iommi solos, I start to strategically apply the cognitive dissonance I know I’ll need to enjoy the show: ignore the cringe-worthy bits; revel in the riffing.