After their costume workshop at the Gellideg youth centre in Merthyr Tydfil, south Wales, some of the girls who had taken part braved the wind and the rain to parade the streets in their finery. It was soon after Halloween, November 2016. They were dressed in black, in extravagant hats, faces pale as the moon. Ice-cold curls, frozen by gel and the weather, snaked stiffly across their foreheads. A few boys skulked around on their bikes to watch the unlikely procession. When the girls walked past, the boys broke into derisive laughter. The girls stopped in their tracks. “It’s called fashion!” one shouted. “Look it up!”

Right then, the photographer Clémentine Schneidermann “realised there was something magical happening”. She had organised the girls’ costume workshop with Charlotte James, a creative director. The photographs the two women took of that seminal outing launched a collaboration lasting nearly three years, between Schneidermann, James and a group of children from the youth centre and the Coed Cae Interact club near Brynmawr. Now a selection of their photographs are to be exhibited in a collection entitled It’s Called Ffasiwn (Welsh for fashion), along with some of the costumes, at the Martin Parr Foundation in Bristol.

Every couple of weeks, Schneidermann, 27, and James, 29, would offer new workshops to the children who attended the youth centres: Schneidermann on photography, for the children who preferred to be behind the camera; James on styling and customisation for those who wanted to model or work with clothes. The workshops were so popular that summer schools followed. In the youth centres, the children – almost all girls – spent hours sewing ruffles and sticking diamante on to secondhand finds. One youth club was given a yellow theme, another purple. They painted flowers on to plain tops, forged pompoms from fur. They braved the sewing machine, swapped and reswapped their pieces, tucked and untucked tops to refine their looks.

All the while, Schneidermann and James documented the children’s extraordinary output, staging carnivalesque shoots in local streets, working men’s clubs, bingo halls and beaches. The resultant images combine social documentary, fashion, landscape art and formal portraiture. “We had no aim. We were just doing it for fun, building something from scratch,” James says. She grew up in Merthyr and returned home to work on this project; she is still there more than three years later.

“Something is keeping us here. We are both really inspired by the place,” she says. “It’s kind of dark,” says Schneidermann, who spent her childhood in the suburbs of Paris and is completing a doctorate at the University of South Wales. “There is no one on the street. Not many young people.” The area has some of the highest rates of unemployment and child poverty in the UK. “You are between two valleys. The sun doesn’t really go through. It’s always in the shadow.”

The landscape is a powerful presence in the images. The children, in their unlikely outfits, look at odds with the world around them, but at the same time blend into it. Weathered house paint chimes with the faded chiffon of a fluttering shoulder. Pebbledash, seen as the background to leopard-spotted leggings, leaps out as a previously undocumented species of animal print. Those extravagant black hats, grey where the light hits, meld with the local granite, as if the costumes, and the girls’ parade have the power to transform the environment.

The colours, Schneidermann points out, are “harmonising” – a decision she and James took to sidestep some of the tropes of working-class imagery. Schneidermann admires the social documentary work of Tish Murtha and Paul Trevor, as well as Chris Killip’s 1980s photographs of the north-east of England. “But we wanted to make [the work] colourful, a step away from how children have been represented in this sort of post-industrial environment,” she says. “Towns are different now. You walk on the street and you don’t see so many children outside.” In Schneidermann and James’s images, the streets of Merthyr and Brynmawr appear carnivalesque yet desolate, the children simultaneously attuned and alien, often tiny figures in a near-matching landscape.

What did it feel like to take part, I asked some of the children. “Like I was walking on a catwalk!” says Keely Arthur, 10, whose lilac trouser suit was inspired by an Instagram image of Kim Kardashian. Poppy Gould, 12, adds: “I liked it. I just walked like me.”

Following up on their colour themes, James and Schneidermann asked the children’s parents how they would feel about having their houses painted yellow or purple. No one seemed to like the idea, so the women scoured the streets. Two roads, Crescent Street and Taff Street, were uninhabited, awaiting demolition, so they strung up purple bunting and festooned the telegraph poles with purple ribbons. “Like a street party. We had them when we were kids,” James says, sounding a little wistful. Fortuitously, one Merthyr resident named Violet lived in a house that was already painted purple, and was wearing purple on the day of the shoot.

“People were laughing, giving us weird looks – some people asked us what we were doing,” says Alisha White, who has just turned 15. She wore a dress made out of laundry bags. “I just thought of my town as my town. But now we’ve done this, it’s made me think it can be more. It doesn’t need to be what you think it is. If you want it to be a background for a photoshoot, then that’s what it’s going to be. The possibilities are endless.”

James relates to that. “I was once a kid from the area. There isn’t easy access to culture. Young people aren’t encouraged to look to the creative industries as a career. I hope the workshops can spark something and encourage creative practice to grow out of small towns,” she says.

Some of the girls dress differently now. Poppy, who used to like jeans, experiments with baggy trousers; Keely, who normally favours dark colours, has bought a crimson puffer jacket. “I never used to wear coloured things,” she says. It used to take her hours to get dressed. If anyone paid her attention, she says: “I would stare back at them, thinking: ‘Stop looking at me.’” Now, she says: “It’s no one else’s choice what I wear.” After all, there is nowhere to hide in a big red jacket. And if people look? “I want that,” she says.

• It’s Called Ffasiwn by Clémentine Schneidermann and Charlotte James will be on display at the Martin Parr Foundation, Bristol, from 27 March to 25 May. A zine accompanying the exhibition is available online, RRP £10.

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