Preview: Blacksand, Channel Four, 'Rockfeedback'

Underground music with risks attached
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By the time we've scrambled down a steep slope to the cave entrance to the Roman mines under Box Hill in Wiltshire, twilight has fallen. The first of our group slides feet first through the narrow opening, then crawls through a low passage into a chamber high enough to stand up in. The rest of us follow in single file. Tonight's performance, perhaps the strangest I have ever attended, is about to begin.

Our destination is called "The Cathedral", a huge chamber in the oldest part of the mine, dating back some 2,000 years. Hunkering down around three small piles of equipment are Nick Franglen and Charles Casey, the musicians who make up Blacksand.

Franglen is one half of Lemon Jelly, and producer of albums by John Cale and Badly Drawn Boy, among others. Casey is one half of Akasha – the original tripped-out purveyors of noirish jazzadelica – and collaborator with Neneh Cherry and David Axelrod.

The two guitarists, with a rack of effects, loops, and gizmos, improvise between themselves, their equipment, and the undergound space. It is an invitation-only event; we are here at our own risk. "One of our friends broke a rib getting the equipment back up to the surface," says Franglen. Another one emerged with a leech stuck to his skin.

This is the second time Blacks and have played before an audience. Their first sessions took place last winter in a calving shed in Sussex. They released the music on the Barn album.

Their subterranean performance veers between the futuristic and the primal. Each performance is unrepeatable, every recording done live. Their next projects include a gig on a Cold War Russian submarine; a trip to a remote gas turbine testing plant somewhere in Hampshire at night will be aired on Channel Four's music series, Rockfeedback.

"Our music is improvised and our journey is improvised," says Franglen. "It has become a kind of psychogeography."

'Blacksand' appear on Channel Four's 'Rockfeedback' tomorrow (