OPPOSITES clash but occasionally they meld, drawing out smouldering brilliance from each other (see the sparks between lovers Jane Birkin and Serge Gainsbourg).

More recently, Belle and Sebastian alumnus Isobel Campbell contacted grizzly-voiced American Mark Lanegan, formerly of the Screaming Trees and Queens Of The Stone Age, for a transatlantic marriage made in sonic heaven - their collaboration Ballad Of The Broken Seas was one of last year's most haunting records.

This year's accolade goes to another beauty and the beast duet: Led Zeppelin's Robert Plant pairing up with country darling Alison Krauss for a deliciously bluesy covers record that evinces sublime inspiration and leaves you high and dry at the end of the set.

Indeed, Raising Sand is that kind of album for which epithets like 'slowburn' are precisely created. It doesn't lacerate; it simmers with molten passion.

Thanks to famed producer T Bone Burnett and a coterie of guest musicians like guitarist Marc Ribot, the atmosphere feels timeless yet visceral - imagine clouds of smoke as Plant and Krauss revel in a dance of rockabilly passion.

The genius is in how the two equals aren't trying to kill or outsmart each other - they are feeling their way around.

Equal parts diffidence and danger, the meticulously chosen songs brood and wrap around the subtle harmonies of Plant's leonine purr and Krauss' pristine country soprano.

Hear how Plant reins in his famous feral growl for a stunning, minor-key tour de force as it shadows Krauss' light-as-gauze vocals in the lovely Killing The Blues, amid languorous slides of pedal steel guitar and percussion brushes.

There's also plenty of sass and chemistry in the excellent toe-tapping single, The Everly Brothers' Gone Gone Gone (Done Moved On), where liquid guitar riffs mirror the intimate braiding of the vocalists.

Similarly deadly is their ghostly take on Sam Phillips' Sister Rosetta Goes Before Us: the sweeter and silkier Krauss sounds, the sadder it is.

Even when things get loud and dissonant, as in shards of electric guitar crashing through in Townes Van Zandt's Nothin', Burnett knows when to wind it down for Plant's gentle killer of a voice to take centre stage.

By the time one gets to the end of the disc wih an old curio by A.D. and Rosa Lee Watson called Your Long Journey, there's a sense that everything has come satisfyingly full circle.

In a setting of banjo, acoustic guitar and autoharp, Plant and Krauss melt into each other, voices caressing like wizened lovers who have seen the best of times and weathered the worst.

Raising Sand
Robert Plant and Alison Krauss
Rounder Records
Rating: ****