SOME jobs require a person to fix a toilet.

Others call on a body to wear a full-length evening gown and attend glamorous events. Kahleen Crawford's occupation might call on her to do both - perhaps even at the same time.

"It's a bit like chess," says Crawford of the multi-tasking life of a casting director heading up her own small firm. "You have to know what your next three moves are."

The 35-year-old Glaswegian will be sharing more of her hard-won wisdom at a Glasgow Film Festival event this Friday. Drawing on her work on the likes of Filth, Sunshine On Leith, Under The Skin and River City, Crawford aims to deliver on the event's title, Close Up On Casting.

Crawford's ability to pick just the right face for the part will be seen next in Under The Skin, a science fiction drama set in Scotland and directed by Jonathan Glazer. Adapted from Michel Faber's novel and starring Scarlett Johansson, Under The Skin is in some ways typical of how Crawford is called upon to work.

From her work on the verite dramas of Ken Loach - including The Angels' Share, Route Irish, Looking For Eric and the forthcoming Jimmy's Hall - Crawford has gained a reputation for being able to cast both professionals and newcomers. With Johansson already on board, Glazer talked Crawford through what he was after. "I've never met anyone who can conjure images in your mind so vividly with words." You can see the results at the festival's closing gala on March 2, or when the film opens nationwide the same month.

Crawford, who will be joined at the GFF event by Kate Dickie (Red Road, Prometheus) recently moved to London, but her firm, Kahleen Crawford Casting, is based in her home city. The Glasgow University graduate in film and TV with theatre studies always knew she wanted to work in the industry, but her route into casting was circuitous. Her first job was in live television production in London, which turned out to be a thankless experience. A phone call from Glasgow decided what she would do next.

"My mum called and said do you want to come home and I said more than anything else in the world right now. I think I drove to Glasgow in two and a half hours," she laughs.

She contacted Scottish Screen, who told her there was a job going as an agent's assistant. Sensing casting would be more Crawford's thing the agent directed her towards Gillian Berrie, the Scottish producer and filmmaker. Crawford was called in for an interview and started the next day, with Berrie putting her in a room with Spotlight directories, a sort of look-book of actors, and encouraging her to get on with it. "Gillian is amazing for that. She has real faith in people and their adaptability."

Crawford got on with the job so well she eventually branched out on her own and now works with two colleagues. Learning how to be a casting director is all in the doing, she says. There are some essential attributes though, adaptability chief among them. People will come to you with problems, says Crawford, and it is your job to sort things out. That takes common sense, being good with people, imagination, and being willing to work beyond the nine-to-five.

While Crawford insists she was "lucky" to be in the right place at the right time, there is more to her success - and the job - than that. A good casting director needs to understand a part and the actor and assess if they are up to the role. Crucially, the casting director needs to see beyond the person in front of them, to picture them in the picture.

With Crawford this started early. She can remember as a child being "obsessed" with actors and their faces. "I also used to write down actors' names if I really liked them and keep them in a drawer. Some of them are quite famous now." That last sentence is the closest she will get to "I knew them when..." Ask her to name those she has talent-spotted and the naturally chatty Crawford shies away from the inquiry. "I don't ever think of it like that. We open the door - they do the hard work."

When it comes to clients, no request is too big or small, though some are impossible, as when an American production company, failing to factor in the transatlantic time difference, asked to see an audition tape before the audition had taken place. Crawford had to point out gently that while they were good, they were not good enough to bend the space-time continuum.

Her job is usually over when shooting starts, but on the Loach films she will be there every day. Loach likes continuity in his casting, so if he decides to add a face to a film after shooting has started it will be Crawford, the initial point of contact, who will book them.

Though she does cast via open calls, most of the time is spent dealing with professional actors and agents. Given the right technology, she can work anywhere. "So much can be done electronically these days. People self-tape a lot, they send you auditions, you can watch show reels."

Having worked on the likes of Filth and Sunshine on Leith, Crawford is among those who dare to hope that Scottish filmmaking is on the up.

"I'm hopeful that it will continue. We have so many talented actors and crew in Scotland. You don't need to bring a crew to Scotland."

For all the ballgown-wearing and toilet-fixing, for all the moving around, Crawford would never trade her job.

"Sometimes you have to give people bad news. But sometimes you get to give them really, really good news and that's wonderful."

Close Up On Casting, Friday, 6.30pm. Festival Club, CCA, Sauchiehall Street. Free - but first come, first served.