ARMED with pens and paint, a crowd forms around The Cube. There are no limitations: a whimsical doodle, a display of love, a confession of sorrow. Hundreds of people offer a moment of time and, together, create a beautiful piece of art.

Edinburgh’s Summerhall art centre is hosting The Cube in its Out Of Sight, Out Of Mind exhibit in October to support those with mental health issues. The project not only encourages self-expression but requires it.

Amid it all stands Mia McGregor. She takes The Cube all across Scotland, determined to bring creativity and colour to different communities.

As the child of two artists, inspiration was never in short supply, and Sunday afternoons were for visiting galleries instead of the park.

In an act of teenage rebellion, at 15 she applied for art school and was accepted into Leith. “But I wouldn’t get into the pubs,” she laughs, “so I decided to f*** off to Germany instead.”

Life in Frankfurt saw creativity take a back seat as McGregor prioritised working – first as an au-pair and later in a pub.

McGregor was still drawing or painting for hours on end, never finding it particularly interesting or exciting but instead very lonely. “Through all of that,” McGregor explains, “I realised the type of artwork I liked, or could thrive in, wouldn’t be the kind I was creating alone.”

The National: Mia McGregorMia McGregor

She wants to unite people with The Cube. “Twenty people stand around a cube and at that moment, in that point of time, everybody’s equal,” says McGregor. Anyone can take part and express themselves while contributing to something larger.

From Germany, McGregor moved to the States with her (now ex) husband. They had three young children, and responsibility fell almost solely on McGregor as her husband was in the army.

Her six years there sound like a traveller’s dream – stints in North Carolina, Chicago, Seattle – but sightseeing was limited to the living-room window. “I was pretty much chained to the house,” McGregor says, “and I think a lot of that was quite damaging.

“I gave everything to the situation but kind of destroyed myself in the process,” she continues. “I knew I was Jake, Max and Millie’s mum, but I didn’t know what my interests were, what I’d do for fun.”

Leaving the States in 2014, she returned to Scotland in search of a better life. McGregor knew that art was her best chance, so attended evening classes to earn a place at college.

Feeling optimistic for the first time in a while, she announced her aspirations and progress to the job centre advisor. The response was soul-destroying: “Look love, don’t you think you should just get a job at Sainsbury’s?”

There’s nothing wrong with working at Sainsbury’s, McGregor explains, “but I’d put so much effort into the evening classes and keeping three children alive. For her to say that this is my best route I thought was very sad.

“And I’m sure I’m not the only one she’s said that to. People with lower self-esteem than me would’ve just accepted it.”

In third year of college she sat planning an assignment. “I was playing with this bit of Blu Tack, and when I’m stressed, I mould it into this cube shape.

“I don’t know what happened. I literally just drew a cube and was like, ‘I’m going to make a cube.’”

She took three to the streets of London and Hamburg, asking strangers to doodle whatever they liked. “And those people meant everything,” she said. “I remember all of them, and not one person said no to me. I think for one moment in time I provide complete inclusion, and we’ll find out what that moment is worth in 10, 20 years.”

Every cube is archived upon completion, creating “a visual timeline of our history,” McGregor says. Over 20,000 people have contributed to The Cube so far, and McGregor hopes it has impacted them and their communities.

The Marine Parade Graffiti Wall in Leith, the largest graffiti wall in the country, has attracted visitors from all over the world, and the council has seen the benefits too, opting to make part of the space permanent.

Mia hopes to create a similar effect with The Cube, injecting splashes of colour into various communities and having them prosper as a result.

She believes it’s still in its infancy though. “It’s like a ripple spreading everywhere.”

However, she admits: “I hope that it gets to the point where I can become quite secret again, so it becomes more about the people taking part.”

She knows it’ll also become more challenging, but she’s ready to adapt. “At the end of the day, I’m just doing what I love.

“And people say ‘Mia, don’t be so sensitive.’ But how can I not? I’ve poured my f****** life into this.”