Sometimes speaking about music isn't enough.

In the middle of describing the form her commission for this year's Blas festival will take, Margaret Stewart abandons the spoken word and bursts into song – a pibroch-style tune she has composed with piper Angus Nicolson – to show exactly what she means.

As she sings, there's no hint of the nerves she says she felt when she presented her musicians with the new compositions that sit among the traditional Gaelic songs and tunes in her Blas piece, The Highland Wedding.

"I've always composed," says Stewart, a Gaelic singer of international renown who grew up singing to the elements on the Isle of Lewis. "I just never let on about it. I'd always be working on ideas in the bath or when I was driving around, but I always thought that what I was coming up with was rubbish. I don't read or write music and I don't play an instrument, so I had to sing into a recorder and I felt physically sick handing it over to the musicians to let them hear it. I had to leave the room and I kept waiting to hear howls of laughter."

The feared derision didn't materialise. Stewart, who has worked extensively on exploring the relationship between Gaelic song and piping, has been around the leading musicians in the Gaidhealtachd often enough over the years to know how well a melody is going to sit on the instruments she's chosen to accompany her as she relates The Highland Wedding, from the opening song that foretells of the great and the good's attendance at our young hero's nuptials through courtship, the bedding of the bride and on to A Bhanais Taigh (the house wedding), which traditionally took place in the groom's house and sometimes went on for days.

"The idea for the commission's subject was mine," says Stewart who is currently musician in residence at Sabhal Mor Ostaig, the Gaelic college on Skye. "I felt I was becoming known almost exclusively for heavy Gaelic song projects dealing in subjects like emigration, the Jacobite era and the Clearances, and I wanted to show that I can sing happy songs, too. Mind you, we're only going as far as the house wedding; we can leave the divorce for another time."

With a vast personal store of songs, she didn't have to do too much research to find suitable material to follow her narrative through. With one or two stages in the relationship's development, such as Suirghe (the courting) and A' Reiteach (the engagement celebrations), no obvious candidates sprang to mind, so Stewart composed her own melodies to fit old texts or a set of dance tunes for her band to play. For the bedding of the bride she has even directed a video for inclusion in the presentation as well as composing a new tune. "The cheek of me," she laughs self-mockingly.

For the wedding band she chose Ingrid Henderson (clarsach), Iain MacFarlane (fiddle and melodeon) and Allan Henderson (fiddle and piano) alongside piper Angus Nicolson, all first-rate musicians with whom she has worked before. More importantly, perhaps, however, is the fact that all four have the Gaelic.

"It makes things so much easier if they know the language," says Stewart. "They understand that I don't want to alter the lyrics to suit the music. It might just be one word that seems like an awkward fit rhythmically or something, but when I sing to them they get the meaning right away and are able to fit the music to the language, which is the way it should be."

With four performances scheduled for the Blas festival, Stewart would like to see The Highland Wedding travel further afield – perhaps down to the central belt – and have a life beyond its initial dates.

"It's always a shame when something like this happens in the Highland area and then doesn't get a chance to be heard elsewhere," she says. "The Highland Wedding itself should transfer quite readily. The songs are easy on the ear and there's quite a lot of music from the band, as there would be at a Highland wedding. My only worry with the band is what they're going to get up to in the second half. When we got together for the first rehearsal they insisted on us all dressing up and it was hilarious, with Allan Henderson playing a very convincing minister and them giving me a shotgun in case the groom didn't show up. I can see I'm going to have to keep my wits about me."

Margaret Stewart presents The Highland Wedding at Magnus House, Aigas Field on Friday September 7; Sabhal Mor Ostaig, Sleat, Isle of Skye on Saturday September 8; Poolewe Village Hall on Monday September 10; and Nairn Community Centre on Tuesday September 11. For full details of the Blas festival 2012, see www.blas-festival.com