Maia Norman likes to be on the move. If one hadn't gathered this from the all-business way she enters a room, her rangy limbs struggling to comport themselves into a semblance of repose while her peppy Californian accent attempts to keep pace with her freewheeling thoughts, there's a clue in her metallic-grey top, which sports a computer-generated print of interlocking motocross tyres. "I'm in perpetual motion," she beams. "If I can run for a taxi, I will. The worst kind of day, for me, is being stuck indoors on the computer." She shudders theatrically. "It makes me want to throw open the door and roll down a wet, grassy hill."
Luckily for Norman, she has the kind of lifestyle where she can barrel down inclines at will. As the partner of Damien Hirst for nearly 15 years (they've never married – "We both come from divorced families," she says, "which doesn't exactly boost your faith in the institution"), she and their three sons – Connor, 13, Cassius, eight, and three-year-old Cyrus – share the trappings that come with being one of the word's most-bankable artists, £50m diamond skulls, record-breaking £95m Sotheby's auctions and all: a north Devon farmhouse with 100 acres of land and Jeff Koons busts adorning the mantelpiece; a Chelsea houseboat; a Mexican beach-house for escaping the harshest strictures of the British winter; and the 60-bedroom Toddington Manor in Gloucestershire, the Gothic pile currently being converted into a gallery for Hirst's formidable art collection. The hill outside Norman's kitchen door in Devon rolls straight down to the North Atlantic coast, where she indulges her passion for surfing (she has "around 24" surfboards). She's also a motocross rider, quad-bike racer, power-boat pilot, and, she adds emphatically, "a complete petrolhead".
In a house full of men, Norman reckons she's the biggest tomboy of all. "I totally play the adventure-dad role," she grins. "I take the kids out boating, fishing and surfing. Damien's the one who sits them down and makes sure they do their homework while he cooks a stew or something." But, while both Hirst and Norman have left behind a hard-partying Colony Room lock-in past, swapping vodka and coke for stew and fresh carrots from their voluminous vegetable patch, there are signs that full maturity may remain some way off. "One of the boys announced the other day that he felt like the most grown-up member of the entire family," she smiles. "I had to concede that he was probably right."
You sense that Norman wasn't entirely chastened by her son's assessment; to her, it's vital to keep a youthful outlook. "It's just so important to me to stay active, mentally and physically," she stresses. The physical side is well in hand, to judge by Norman's lean frame, blonde mop, and glowing skin – at 46, she could pass for a decade younger – and the mental exertion is being deployed in the relaunch of her fashion line, Mother of Pearl.
The spring-summer 2009 collection is a riot of wardrobe staples – hoodies, blazers, little black dresses, biker jackets – amped up with zips, luxed up in lamb nappa, or performanced up in hi-tech Nano- and -ology sports-fabric claddings. It's the kind of capsule wardrobe that could take the average Outward Bound art-world luminary from quad-bike trial to gallery opening, pausing only to brush the mud off her hem – "which is just how I like it", grins Norman.
Mother of Pearl's previous incarnation was as a beachwear label, with Native American prints splashed across swimsuits and modelled by the likes of Mick Jones' daughter Lauren. So why the relaunch now? "Because I finally realised what my vision was," says Norman simply. "I wanted to change from the beachwear angle to much sexier and edgier, with more street and sport in there. The active side was really important to me, because I'm not about stagnancy at all."
Also, she adds, the key this time was less about transient fashion and more about enduring style. "I wanted to make that leather jacket that you just adore and becomes your best friend," she enthuses. The shirt she is wearing, with a tyre-print designed by video director Alex Rutherford, is part of the collection – "When you see a motocross bike, it just makes your heart race, right?" she asks rhetorically – and future collaborators will include artist Matt Collishaw, a YBA contemporary of Hirst and former boyfriend of Tracey Emin. "It's handy to be able to call on people like Matt," she concedes, "but the thing with Damien and his generation was that their friendships were so strong ' – they'd lend money to each other when they absolutely had none – and they remain so. It was all part of their conviction, their determination that they would get somewhere." Though nowadays, she allows, as they creep toward their fifties, they might have to adopt a new acronym – perhaps the Slightly Older British Artists, or SOBAs, which would be oddly appropriate, given she and Hirst forswore alcohol some years ago.
With this collection, Norman hopes to bury the notion that she's some kind of fashion hobbyist or dilettante. "On paper, I don't need to work," she says. "I could be a surfing housewife. But it wouldn't be creative enough for me. We're going to be doing two collections a year, and it'll be a real challenge to keep the ideas going. Then there's the commercial side."
Mention of the "c-word" prompts the question of whether Hirst, no slouch in the business of selling himself, had given her any advice. "He taught me a lot about not settling for anything less than my total vision," she says, "which really stopped me from giving this up, and helped turn it into what I wanted it to be. And Damien's still so vibrant about what he does, and still brimming over with so many ideas. That's really attractive to be around, not to mention infectious."
Norman believes in the power of positive thinking. "I've always been so responsible for myself," she says, with something of a battle-hardened air. She was brought up in that part of southern California now rebranded as the OC, in a classic arty-boho household. She never knew her biological father, who died when she was 16, while her stepfather managed rock bands; Norman, who assumed housekeeping chores, would end up dusting round supine members of the Red Hot Chili Peppers and their ilk (and, according to an earlier interview, suffering abuse at her stepfather's hands – a subject that she is unwilling to discuss today).
Norman discovered an early interest in clothes – her mother, "a beautiful seamstress", would run her up bespoke prom dresses – and by the time she was 18 she'd gone through a rockabilly phase ("I had a dyed-red quiff and a '55 Chevy, and I managed the aerobics-wear shop next door to Jane Fonda's workout gym, bossing these Beverly Hills matrons around in my pointy shoes like a dominatrix"), to embrace punk's DIY ethos – and display an enduring gift for finding herself in the right place at the right time. "I got offered a singing contract just before I left LA," she grins incredulously. "I was like, 'But I can't sing.' And they said, 'But you've got the look, it doesn't matter – look at Steve Strange.' So I went through four months of coaching before we finally gave up." She shrugs. "Life deals you these kinds of opportunities. I guess I've always steered toward creative scenes and creative people."
She left for Europe in 1983, attending art school in Paris. She didn't graduate, but stopped off in London on her way back to the States, showing her Gothic jewellery designs in James Birch's Chelsea gallery (who also had the young Grayson Perry on his books at the time), working for jewellery designers Erickson Beamon, and squatting with a girlfriend in Notting Hill, where she hung out with the likes of designers Tom Dixon and Georgina Godley and DJ Rachel Auburn, and was assumed into the mid-1980s boho-cracy. "The neighbourhood was hopping at that time," she recalls. "There were always parties going on. It was such a different mentality, so spontaneous, which LA never is."
Norman's return home was endlessly deferred. By 1989 she was going out with Hirst's dealer, Jay Jopling, and getting intimate with the emerging YBA scene; she became one of Hirst's first assistants – she was responsible for the first 10 spots of his spot paintings – and then, somewhat messily at the time for all concerned, his girlfriend. It now seems inevitable; Hirst had also never known his father, and, says Norman approvingly, "He brought himself up. I recognise that sense of self-sufficiency. And he made me laugh. Still does."
The lineaments of the relationship, at least as Norman has described them in the past, have a touch of Bonnie and Clyde-esque bravado about them: how, when they met, Hirst slept on a mattress on the floor of a rented room in a council block; how she'd drive him to maggot farms and derelict hospitals to pick up old medical supplies, stopping off to fish furniture out of skips; the late nights of Olympian socialising, when Hirst's extendable foreskin became as familiar a Soho sight as any hand-scrawled "Model – First Floor" notice. There was a time, Norman admits, when they'd collect all manner of human flotsam and jetsam around them. "Now we've come through the whole drink and drug thing intact, and the only strays we pick up are cats and dogs. I've discovered I'm not that great at being a guidance counsellor. There's only so many times you can tell someone to get themselves together."
By far the biggest difference between then and now is Hirst's position on the Rich List; he's regularly credited with at least eight noughts to his name. Norman's attitude to their redoubtable wealth is admirably sanguine. "I take it pretty lightly," she asserts. "The revelation, to me, was that having money didn't automatically make everything absolutely amazing. Most of the things I love don't depend on having money. It's more who you're around, the situation you've built for yourself, and your creativity. You can't buy that."
Norman's philosophy in the face of all of life's vicissitudes – not enough/too much money, overindulgence/sobriety – can be boiled down to a two-word mantra: stay strong. "Physical strength leads to mental clarity," she says in her most ringing California can-do tones. Her overriding fear is not of illness nor poverty, but of becoming a slob. "Damien's always trying to say to me, 'Look, it's OK, slob out,''' she grins. "I'm like, 'No honey, I've got things to do, look at my lists.' I'm always making them, and working my way down them, ticking things off," she says, tugging at the hood of her jacket. "When life gets busy you've got to prioritise. Mother Of Pearl's taking up more of my time now, but I can't let the rest of my life wane." And Maia Norman jumps to her feet, ready for the next thing, running just to keep up with herself.
Mother of Pearl will be available from Start London and Maxfield in LA from February; www.motherofpearl.co.uk