After earning degrees from Paris to Massachusetts, the artist now known as ELLE found her work consigned to an all-too-common fate. “Everything was getting rolled up and put under my bed and just dying. It was like this graveyard of paintings.”

She quit art and moved to New York. Bartending kept her afloat, but the city’s street art scene pulled her back in. She began painting on paper and pasting it on walls. A few years later she had a line of Reebok sportswear, was fielding calls from Samsung and Toyota, and became a fixture on streets from Miami to Melbourne. One of her latest pieces will span the entire hull – more than 320 metres – of a Norwegian cruise liner. Have spray can, will travel.

ELLE’s work is among more than 100 pieces of street art featuring in The Outsiders Melbourne, an exhibition built from the collection of Melbourne couple Sandra Powell and Andrew King. The power couple – “Sandrew” to their friends – have spent more than 15 years throwing serious bucks at street artists worldwide. “You’re going to have a hard time finding an artist who has anything bad to say about Sandrew,” says ELLE. “They’re like the parents of the street art scene in Australia.”

Among the thousands of works they’ve purchased, Powell and King have the biggest collection of Banksy works in Australia. There’s a whole room dedicated to the British street artist in the exhibition, including a new piece that hasn’t been seen before. The show will also feature works perhaps less familiar to local audiences that merit the kind of serious attention street art demands today.

Caledonia Curry grew up in a chaotic household at the end of a dirt road in Florida’s Daytona Beach. In this dumpy little backwater, she learnt about art the old-fashioned way. “You went to the library and got books. My version of what art could be was really circumscribed. So when I got to New York it was like the lid came off,” she says.

Today she’s better known as Swoon, one of the most respected street artists of her generation, ranked alongside Banksy and JR. She’s spent decades pouring her heart into work that has mostly been scrubbed from the walls. “When I started it was very scrappy and very illegal. Very street level, get it done and get out. And I personally love the impermanence of those works, and that wildness.”

When Swoon and her peers were finding their feet, street art hadn’t accrued much respect in the broader art world. Powell and King were ahead of the trend. “It was such a young movement, everyone was in their 20s and travelling the world and no one knew what was happening, and Sandra and Andrew were kind of there, like family for everyone,” says Swoon.

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Street artists travel a lot to stay at the forefront of the scene, and Powell and King have long offered lodgings for travellers looking for a new canvas. “Sandra and Andrew have this amazing guest house, and now they have a penthouse as well that they put artists up in,” ELLE says.

The same can be said of Everfresh, the Melbourne studio founded in 2004 and home to some of Melbourne’s most prominent street artists. “Everfresh always had a bedroom, so any artist that came in could stay there,” ELLE says.

One of Everfresh’s current residents is Drez, whose striking “chromatic pulse” paintings have been hailed as pushing street art in a bold new direction closer to the traditions of op art and cubism.

Drez began doing graffiti with friends in his teens, but admits that scene at that age can be dangerous. “There’s a lot of young boys around trying to one-up each other and be the toughest person in a stupid, overly masculine way,” he says. “I was not interested in that, I’m very opposed to violence, so never got into the more macho stuff. I definitely had friends that sat in that lane and heard stories, but personally, I was interested in painting and developing my style.”

By the time he was in his 20s he’d studied at the Victorian College of the Arts and was earning a living creating art within the music industry, so he didn’t need to think about the commercial appeal of his street output. At the same time, he says, “I didn’t like how there was a very broad demographic of people that didn’t take street art seriously at all. I wanted to put work into graf-oriented locations that really spoke to a different audience.”

Now Drez’s art sells for four- and five-figure sums. He’s just completed a commission spanning two square kilometres on the Princes Freeway near Laverton.

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There’s an irony to the title The Outsiders, given how broadly street art has been embraced over the past decade or so. Institutions add works to their permanent collections, while individuals and businesses commission original art for their walls. We might well be at a tipping point where the line between street art and public art is erased entirely.

But street art has always been public art, in a sense – the only difference is who pays for the paint. It’s fitting that the city that spawned democracy is also one of the most heavily graffitied: Athens is plastered with political statements that are then answered by others, and as the responses build, you can’t help but feel as though entire debates are taking place in public. Which, to some, is the point of art.

If we think of art as a conversation between a work and its viewer, traditional public art can often feel like small talk. The shiny baubles that adorn the forecourts of countless corporate plazas aren’t intended to arouse powerful emotions or conflicting thoughts. That can change when street artists are given permission (and funding) to add their voice to the conversation – or as Swoon puts it, “coming to people where they are”.

But with street artists increasingly finding themselves courted by galleries and private collections, the obvious question arises: what happens when the outsiders are invited inside? What is street art without the street?

For starters, it sticks around. For all her love of street art’s impermanence, Swoon acknowledges there’s a “part of my heart that doesn’t want every single gesture of the movement to be fleeting”.

“I put hundreds of thousands of hours out into the street and then they just vanished. I’m happy for that to have happened. But I’m also really happy that there is a record and that it can be shown and shared.”

The Outsiders Melbourne is at 167 Flinders Lane from December 12.