What do sean nós and the blues have in common? More than you might think, as two performers tell Siobhán Long

We all know how contrived the packaging of music can be. Why was Johnny Cash filed under 'C' for country when he could rock as hard as Nine Inch Nails and trawl the depths of the blues with the conviction of Brownie McGee? Aretha Franklin has made soul, pop and rock 'n' roll all her own; and Clare accordionist Tony MacMahon has poked and prodded at the borders that supposedly separate classical and traditional music with the Kronos Quartet. Music wasn't invented by trigonometry teachers, identifying the precise angles at which tunes begin and end. Mercifully, it's a much more free-spirited beast that bucks against every corral imposed on it - even if at times the Simon Cowell/Louis Walsh effect reigns supreme.

The crossroads where sean nós singing and delta blues collide is the spot where singer and actress, Mary Ryan, and blues guitarist Dermot Rooney have pitched their tent of late. Ryan is an accomplished actress who forged her reputation with Druid Theatre Company, and spent a spell in the company of Jim Doherty in a show called Wild Women Don't Have The Blues, and with Susie Kennedy and John Dunne in Wild Women Meet The Hoochie Coochie Man. Rooney is a Belfast-born slide guitarist steeped in the blues of the 1920s, whose affinity with Blind Willie Johnson has taken him deep into the belly of what he considers one of the most complex musical forms.

"I am basically a blues singer," says Ryan, "but I wasn't in any way as steeped in the blues and gospel music of the early 1920s as Dermot has been. I'd always sung sean nós songs too, and what evolved for us both was a sense of the similarity between the two forms. Sean nós is so much about the voice. The singer is carrying the emotions, traditions, culture and history of Irish people, and blues songs capture the culture of black people. Both types of singing are very emotional - you just have to go for it."

It's the lyrics, the motifs and the images conjured in the sean nós songs that travel most successfully, according to Ryan. This, she says, is evident in songs such as Prisiún Cluain Meala, an execution song about one of the illegal Whiteboys who lists what he wants at his funeral. This tale traversed the US and re-emerged as a cowboy song - some would insist it's about Jess James. It's sometimes known as The Ballad Of The Dying Cowboy, elsewhere it raises its head in the guise of The Dying Crapshooter's Blues, with the same images as its ancestral forebear from Clonmel.

It's not just the emotional depth charges in sean nós and blues music that spurred Ryan and Rooney toward developing their repertoire. They reacted to the compatibility of slide guitar and voice with equal enthusiasm. "I find that the voice will try to emulate an instrument," Ryan notes, "and with the slide guitar, which can come so close to the voice, I find it makes me sing from a much deeper place, it makes me go far deeper into my body."

Dermot Rooney expresses no surprise at the coalition he and Ryan have formed with Sean Nós Meets The Blues. The fact is, people travelled, and their music emerged in new cultures with an altered identity, but one that fitted in with its new surroundings.

Rooney's life-long love affair with the blues is reaching fruition in a particularly original form with his collaboration with Ryan. In his view, very few musicians have matched the complexity of Willie Johnson's and Blind Willie McTell's musicality in recent years. "Only one player that I've heard has come close to that 'blind' technique, taking the music of Johnson in a new and very special direction, and that's Ry Cooder. What he did with Paris Texas was based almost entirely on a Willie Johnson tune called Dark Was The Night."

Rooney is hugely respectful of the artistry of those old Delta blues musicians, the best of whom were blind.

"I think the fact that one of the senses wasn't functioning, sharpened them up on other strengths," he suggests, in an attempt to explain the virtuosity of Willie Johnson and his peers. "You just don't hear musicians reaching the heights of McTell and Johnson. They all fall far short of the original."

Sean Nós Meets The Blues is on a 25-date Irish tour, including: Draíocht, Blanchardstown, tomorrow; Áras Cronán, Clondalkin, Sat; Seamus Ennis Centre, The Naul (2pm) and Pavilion Theatre, Dún Laoghaire (8pm), Sun