AHEAD of meeting Alison Watt in her studio in Edinburgh's New Town, I dig out an old diary.

In an entry dated October 5, 1997, I find myself at the opening of Fold, the Greenock-born artist's solo show at the capital's Fruitmarket Gallery. She would have been 31 at the time.

This being the era when Becks' sponsorship of the art world was extensive and generous, I see I've written a great deal about the free beer and nothing at all about the art. But my younger self has been far-sighted enough to paste into the diary two postcards showing paintings from the exhibition, and for that I thank him. They are Sleeper: Fragment II and Madame Riviere: Fragment V, diptychs combining female nudes with images of crumpled fabrics, sheets and floral wallpaper. Looking at them now I can see why Watt was then fast becoming one of the stellar names of Scottish painting, and how their style and subjects were predictors of the artist she would become and the work she would later make.

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One other detail in the diary entry stands out: Madonna had been invited to the opening too. I'm still curious about that. Did the star ever show?

"No," laughs Watt. "Well, I certainly don't remember her arriving. You'd have heard the helicopter. She certainly has a tremendous art collection and she" - there's a pause here while the right word is selected - "flirted with coming to see me for quite a while. But it never did happen. If I'm right, I think in her New York house at that time she was collecting female nudes and that's where her interest in me came from. John McEnroe has a painting of mine and she'd seen it."

So that clears that up. But, 17 years on, asking Watt to dig out memories of exhibitions past isn't just my way of trying up loose ends. On Friday, she has another opening to attend, one which also involves trawling the archives and confronting moments and memories from her career to date.

Alison Watt: Paintings 1986-2014, a retrospective at Perth Museum & Art Gallery, is being mounted as part of the National Galleries of Scotland's ongoing Generation series. It isn't a huge show - Watt has selected 20 paintings - but it brings her face-to-face with some works she hasn't seen for decades and, in the way of these things, with manifestations of her younger self which are every bit as potent and emotive as an old diary entry.

"You have that experience of being taken back to a particular time and place and remembering how you felt," she says. "In terms of how you feel when you make a painting, that's not an altogether pleasant experience because making a painting, for me, is an emotional experience and it's an intimate thing because it's about what lies inside. So it's a bit odd. You're seeing a map of your life, in way."

Among the paintings on display in Perth is one of the ones I have glued into my diary - Sleeper: Fragment II - as well as Source III (from 1995), a 1986 self-portrait which is the first painting Watt ever completed, and Phantom, one of the seven large-scale works she made between 2006 and 2008 while in the position of artist-in-residence at the National Gallery in London. It was subsequently bought by Glasgow's Gallery of Modern Art for £45,000.

But as well as accessing old emotions, revisiting old paintings has given Watt the chance to look coolly and dispassionately at what she calls "the trajectory" of her work. "You see certain themes running through it, things that occur and re-occur, things which have maybe left the work and other things which have remained but altered in form," she says. "So yeah, there's a definite narrative going through, from the mid-1980s when the show begins, to now."

A narrative about what? "If I could categorise the thread that runs through the whole thing, it's probably the human presence," she says. "In the beginning it's explicit and now it's much more ambiguous. But that is the thing that joins everything together."

She's referring, I think, to the change in style which that 1997 Fruitmarket show introduced and which she built on three years later in Shift, a solo exhibition at the Scottish National Gallery of Modern Art in Edinburgh. It featured a dozen paintings whose enigmatic subject is the one now most closely associated with her - apparently black and white studies of what look like folds and creases in what may be bed sheets, shrouds or drapes. Many have a dark, fathomless central point which makes them suggestive of the curves and crevices of a woman's body. It's a reading Watt doesn't dismiss.

"The sexual element is often commented on," she says. Moreover she's perfectly open to it. But, she adds: "Once your work goes out into the world you can't control it and what people think about the paintings has very little to do with me. Quite often people say: 'That reminds me of X', and I'll say 'But that's more about you than me', because we all carry around our own sensibilities which we project onto things."

What's beyond doubt is that after a decade of working with life models or putting herself into tableaux she describes as showing "frozen ceremony or ritual", Watt started the 21st century by taking the people out of her work - but did it in such a way that she left an impression of them behind.

"I still think my work is very figurative, it's just not explicitly so. The body is very much implied. I think the reason I make the paintings I make now is because there are certain proportions that are satisfying and make sense to me, and that comes from my fascination with the human body."

Not that leaving the body wasn't a wrench. Watt tended to work with the same female life models for years at a time, to the point where she viewed them almost as a collaborators.

"I worshipped them and often in a certain sense fell in love with them because they were giving me something," she says. "Even when you have a partner or a husband or a lover you vary rarely get the chance to study their body. You can be with someone you've known for years but not really know the intricacies and intimacies of them physically. And being able to do that with someone was a huge privilege. I absolutely loved it and I loved the intensity of that, the intimacy."

The presence I find most explicit as we sit in a room adjoining Watt's studio is equine rather than human. An enormous horse head skeleton is sitting on the table next to us just asking to be asked about.

"When we were growing up we knew a vet and my dad used to do a bit of taxidermy so sometimes he would give us things," Watt explains matter-of-factly. "I learned about anatomy from my dad opening things up and showing me."

Her father is James Watt RGI, noted painter of boats and maritime scenes, a co-founder in 1957 of the Glasgow Group and, like his daughter, Glasgow School of Art-trained.

The vet, meanwhile, had been instructed to castrate a shire horse but when the scalpel touched the creature it dropped dead from shock. So he popped round to the Watt house with the animal's head - "like the Godfather" - and it was duly buried in the back garden then, later, boiled. "It's a gorgeous thing," says Watt. "It's really, really beautiful. I have a collection of taxidermy as well."

She does indeed. There's a Golden Eagle in a case in the studio itself and behind me on the floor-to-ceiling bookcase, a stuffed budgie on a perch. Elsewhere there are busts, marble statues and, on a table by one of the three huge windows that flood the studio with light, Kilner jars filled with brushes and tubes of oil paints arranged in a neat row. On a sheet of stainless steel beside them are gnarled fists of dried paint in black, white, mustard and ochre. On the walls, half-a-dozen or so paintings from an as-yet-untitled new collection. One of them is also destined for the Perth show.

After years of renting studios and doing them up to her landlords' eventual benefit rather than hers, Watt decided to buy her own space a little over a year ago. Employing an architect, she had the boarded-up fireplaces revealed and the ceiling raised. "I think somebody was growing cannabis here," she laughs, referring to the 40 electrical sockets she had removed.

This is an important space for her, though. "When I was a child the place I felt most at home was in my dad's studio," she tells me. "I used to go in there when he wasn't there. I liked that idea of being separate."

It's a habit she maintains in her own life. Now divorced from her journalist husband, she lives with her new partner elsewhere in Edinburgh and walks to the studio through the New Town. Here she works office hours, or longer if need be under special lights that replicate daylight. And of course there's a radio, the link with the outside world that no artist seems to want to be without.

As if the retrospective wasn't enough, Watt also has work in another Generation show: a group exhibition opening at the Scottish National Gallery of Modern Art on June 28. She's showing Sabine, one of the works that featured in Shift in 2000 and which was inspired by fabrics in paintings by 19th century French artist Jean-Auguste-Dominique Ingres.

Watt has also just completed a collaborative project with Edinburgh's Dovecot tapestry studio. Titled Butterfly, the tapestry is five-and-a-half metres by four and has been commissioned by Scottish Opera to adorn the new foyer of Glasgow's Theatre Royal. Imbued with Watt's trademark sense of ethereal mystery and based in part on Japanese kimono design, it's a beautiful work. What's equally notable, however, are the vibrant colours it employs: pinks, purples, yellows, lilacs.

Watt doesn't accept my description of her paintings as monochromatic - in fact she drags me off to peer closely at one of the canvases in the studio and certainly proves the point - but she admits that Butterfly required her and head weaver Naomi Robertson to think deeply about colour. These conversations alone took weeks, the weaving lasting a further nine months and the whole project took two-and-a-half years from start to finish.

Watt has recently made a helpmate of sorts of poet Don Paterson. He published a response in verse to her 2008 collection, Phantom, and the pair collaborated on her 2011 show at Edinburgh's Ingleby Gallery, Hiding In Full View. In it, both poet and painter responded to works by American photographer Francesca Woodman, whose startling and sometimes troubling images - self-portraits and nudes with faces blurred or hidden - hint at the unrest which caused her to commit suicide in 1981 aged just 22.

In fact poetry is increasingly becoming a major source of inspiration for Watt. A current favourite is Norman MacCaig and she says there's as much writing in her sketchbooks these days as there is drawing. "There are shapes within the paintings I'm making now that I'm not exactly sure where they're coming from," she says. "Before, I was more directly referencing Old Master paintings but it could be that the poetry I'm reading is having an effect on the painting."

Another change is possibly less welcome: it's actually becoming harder to paint. She tells me about a thought-provoking meeting she had with august British artist Leon Kossoff during her stint at the National Gallery in London. Now 87, he was mounting an 80th birthday exhibition there. Under such circumstances you'd think he would have had nothing to prove. Not so, says Watt.

"His fear about the actual act of making was palpable. He's still working but at that point he didn't know if that was going to be his last body of work and he was terrified about that being the thing he was remembered for. I hadn't really thought about the future of my painting in that way. I had hoped that it would get, not easier exactly, but that I would know more about what I was doing. And it just doesn't happen.

"It's taken me 25 years to work this out - but I actually know virtually nothing about painting, even though I do it every day and I look at it all the time."

What she clearly doesn't expect is answers - though ironically it's that fact in itself which keeps her working.

"You are, when you make a painting, in effect trying to solve a problem and it's a problem that's never solved. That's the driver, that's what keeps pushing you on to keep making, because you want to make something that's worthwhile or better. And it just never happens.

"It's always," she says finally, "somewhere off in the distance."