WHEN are we most truly ourselves? Dressed for office or weekend? Dolled up for a date? Wearing a masquerade costume expressing our secret self? Or wearing nothing at all? After all, if you believe the new wine advert, "the more you see of someone, the more of someone you see".
Is the unclothed body a manifestation of God or a reminder of shame and sin? Does removing markers of rank and status reveal the true personality, or are our chosen adornments more telling than flesh, which we can't always control? Does nudity celebrate dignity or emphasise fragility? These intriguing questions arise from a new exhibition featuring more than 180 works from artists as diverse as Diana Arbus, Francis Bacon, Mark Quinn and Lucien Freud.
It's called The Naked Portrait. Journalists heard that the title was chosen provocatively, to question the difference between naked and nude. But when I ask the curator, Martin Hammer, about this, he demurs. When his idea for a broad survey of modern portraiture proved too vast to tackle, Hammer zeroed in on the nude as a singularly modern feature of the genre.
"The title is straightforwardly borrowed from a series of Lucien Freud paintings called The Naked Portrait," says Hammer. "The more I thought about it, the less useful I found it making a distinction. Kenneth Clark said that nakedness was in everyday life, nude was what happened to the body when it was transformed into art. More recently, nakedness was used to distinguish between art that's very warts and all and art that is more idealised or generalised. To the extent that a portrait is about the particular individual, and especially when you're using photography, then it will be very warts and all. So the term naked is useful."
The ancient Greeks revered the male nude, which represented their ideal of divine beauty. That's why there's a sameness to the physiques, since artists worked to exacting measurements. Here, where climate dictates that clothes are the norm and the Judeo-Christian ethos predominates, nakedness implies sinfulness and shame, especially for women.
"One of the first things people will see is a bronze of Eve by Rodin, precisely to acknowledge that we make up stories like Adam and Eve to express the deep-rooted sense of shame that is a fundamental feature of our culture," says Hammer. "To enjoy the exhibition people need to overcome that embarrassment and shame about looking at the human body. There has to be a willingness to take an interest in what the body reveals about the self and others, the diversity of bodies."
Some artists have had their work labelled obscene, though surely obscenity is in the eye of the beholder. Still, I'm curious: what's the difference between a naked portrait and a Page Three "stunna"?
"The Page Three picture is aimed at producing only one response, a kind of sexual frisson. I hope the work in this exhibition produces a more complex response. That's the wider distinction between art and popular culture: art's trying to deal with more complex issues and meanings. Even if you are looking at a body which you might find interesting from a sexual point of view, the image will work for you on other levels. Nothing here was created solely to produce a sexual response."
Some will stay away, and that's fine, he says. The rest of us will be invited to contemplate body language and how artists use gesture to individualise a sitter.
"In the section about loved ones, nakedness is seen as appropriate to conveying the tenderness and intimacy inherent in a loving, sexual relationship. Another section contains images of family, representing the desire to cut across the clichs and portray in a more meaningful way that sense of intimacy and family bond. There are images by artists of their own children or of their parents."
Here you'll see work by Elinor Carucci, who has been photographing her family naked since her teens. It is, she has told interviewers, partly a reflection of the casual atmosphere when she was growing up. She was amazed when viewers expressed shock, but equally startled when they admitted they'd never glimpsed their own parents naked.
Another section features naked self-portraiture, which developed in the 20th century. "Nakedness has connotations of self-analysis, self-exposure, self-revelation. There's strong input from female artists, with the idea of reclaiming the body in the sense that it's a sexual object. They want to present their own bodies on their own terms," says Hammer.
"What's interesting about the exhibition is that often the fact of nakedness quickly merges into metaphor and suggestions of the naked truth, or biblical imagery. Vulnerability is a key theme. Two things viewers might take away are the diversity of humankind in terms of age, shape, size and colour, and vulnerability: nakedness suggests mortality."
This interests me. Years ago I posed mostly naked. I wasn't the subject of the picture, which was an author photo for a book of work by a South American painter, but because I lifted weights and he painted figuratively, they wanted my musculature as the backdrop for his portrait. I didn't know him and was only casually acquainted with the female photographer.
I felt intensely awkward stepping out of the dressing room, but I decided I had started so I'd finish. Dropping the robe was unsettling - but lo and behold, the sky didn't crack with thunder, the earth didn't split and swallow me, and nobody laughed. The mood was so professional that I grew blas, forgetting I was undressed. I found it empowering.
So while the flesh is weak, there's a case to be made for nudity as the ultimate show of strength, a very literal manifestation of the French expression bien dans sa peau. Here I am, take it or leave it. When someone not only takes it, but transforms you into art, there's a palpable surge of power.
I'm not alone in this. Reading blogs by participants in Spencer Tunick's mass nudity events - performance art as much as anything, admits the photographer, who refers to his work as "flesh architecture" - I find my thoughts echoed. Gavin, blogging on takeoneonion.org, participated in a shoot at Selfridges in 2003. "I've never seen so many naked people and it is a surprisingly freeing experience. Once someone has no clothes on, many differentiating factors disappear and you are left with sex, colour and age... It was not a sexy experience. It felt quite matter-of-fact." Afterwards, many participants stopped to discuss their reactions. "You have the oddest conversations about nudity," says Gavin. "It has also gotten me thinking about the representation of who we are and how we are depicted... It has given me an idea of the variety of the human form and how one person can use it as an artistic medium."
Precisely, says teacher and life model Thomas Alexander, one of the authors of Academic Undress (Melrose publishing, 14.99), though he does separate naked from nude: "Nakedness implies vulnerability and nudity is perfectly all right, as in a nudist camp. It really depends on the observer. Those people who make the model feel vulnerable ought not to be there. There's near pornography and real art. Where is the boundary? It's difficult to state. Beauty and pornography and obscenity repose in the eye of the beholder, not in the thing being viewed."
And the great reveal? "It's like jumping off the high board. I couldn't care less. They need somebody old and wrinkled and that's me. I've been modelling about half my life and I'm 80 now. It becomes addictive. I think it's about massaging the ego. I am pretty horrible to look at, but I can stand still. Art students want a mix of old, young, black, white, male, female, hairy and whatever. A lot of the satisfaction models get is out of having been the stimulus that lets someone create something."
The most frequently recurring subject in art is the human face and body. The Naked Portrait exhibition offers a very affirmative, if occasionally sombre, view of what it's like to occupy a human body. Hammer says: "Some of the images are bleak and quite distressing, others more optimistic, even humorous. There's a series of fantastic, moving images by Emmet Gowin of his wife, which he began in the 60s and is still making. It's a meditation on time and ageing and his continuing devotion to someone.
"A sculpture by Marc Quinn comes from his series of images of disabled people, who are, as it were, imperfect, but who he portrays through the artistic language and materials of classicism. Why do we look at the Venus de Milo and think of it as the embodiment of the perfect human body, even though it's got bits missing, whereas we look at someone in real life who's got bits missing and avert our gaze and feel embarrassed? His work is about that interesting dichotomy in our attitudes. So again, we're looking at the way artists use the tradition of the nude and in some ways subvert it."
There is, Hammer concludes, something here for everyone in the show. "It's very accessible. You don't need to know any art history to respond to these works. Everyone has a body; everyone is potentially naked."
• The Naked Portrait, Scottish National Portrait Gallery, 6 June until 2 September