The process can also be bumpy. Pianist Peter Donohoe was a shaggy, bearded Northerner until EMI took him in hand, put him in spivvy suits, and photographed him peeking coyly from behind an up-ended keyboard. "We wanted to make him attractive to the 25- to 35-year-olds who are coming away from pop," explained the company's product manager. This particular product rebelled and reverted to type, but no matter: sales went up, which meant the image had done its job.
Sometimes it's just a question of calling in a hairdresser. The baritone Bryn Terfel admits that his leonine hair-do was the suggestion of a judge at a Guildhall competition, who was appalled by his pudding-basin crop. He's grateful: he feels good, and the critics all say how good he looks.
The latest classical artist to get the make-over treatment is the clarinettist Emma Johnson. "I told her, you're a woman now, so you must look like one," says her ebullient publicist. Johnson obediently put herself in the hands of a new hairdresser - for that just-out-of-the-bath dishevelled look - and submitted to long sessions with a Knightsbridge couturier, where designs by Moschino and Conran finally won the day.
"I've had to accept that, for a female performer, what you wear is inescapably important," explains Johnson. "We don't have the option of the anonymity of the penguin suit. And if we make it obvious we don't bother about our dress, people take that as a statement as well."
So? "I wear a lot of black, if possible with something witty about it. But understated, so you still feel the music is the main thing." And the hair-do? "It matters to me that I shouldn't have to think about it, so I can concentrate on what I'm doing. People who have the longest careers do so by their music. Marketing can get people to buy an artist's first record" - are you listening, Vanessa-Mae? - "but, beyond that, it's a question of quality."
She admits, though, that the make-over was a calculated attempt to solve a problem. Having won the BBC's Young Musician of the Year award in 1984 - aged 17 - she was finding herself increasingly imprisoned by that aura. "I began to wonder if it would ever stop, if they'd still be calling me `Young Musician of 1984' when I was 60. I had to do something about it."
She also admits she had reached a creative plateau, which may itself have been a delayed effect of that award. She had found herself, like James Galway, the darling of the Radio 2 easy-listening brigade, though - unlike Galway - she did her best not to succumb. "People accused me of selling out, but I hadn't. It was just that my concerts were for family audiences, who didn't want to know about the music of Michael Berkeley."
They certainly didn't. "When I did Michael's clarinet concerto" - a piece she commissioned herself - "some people came up afterwards and said they hated it so much they wanted their money back." She loyally insists that this unlovable work is "a very powerful piece to play", but accepts that those who pay for a concert after a hard day at the office have a right "to be delighted, or moved, or taken out of themselves in some way."
At her Festival Hall concert on Friday she will be premiering another work written expressly for her - a clarinet concerto by John Dankworth. It's very jazz-influenced, she says - "with a feeling of Cleo Laine improvising over a tune" - and technically very demanding. She had a hand in its composition, persuading Dankworth to extend a section she liked, and acting as his adviser on technical aspects. Jazz proper she leaves to the professionals, but Benny Goodman and Artie Shaw are among her heroes.
Two of her others are more surprising: the baritone Dietrich Fischer- Dieskau, and the pianist Artur Rubinstein. "These people are totally compelling. They involve your ear in what they're doing from the moment they start. They use a lot of colour, and they take real risks - they never churn out safe performances." Listening to what she does with Carl Maria von Weber's concertos - noble works by a contemporary of Beethoven - it's easy to believe she's taken those lessons to heart. Her technique is flawless, her tonal range impressively wide.
But it's an odd thing, the clarinet. People don't love it as they do the violin or cello. Why? "I don't know why. Beats me. Until Mozart came along, the best composers didn't even write for it. It was universally seen as a peasant instrument. I suppose I'm trying to rectify this situation in my work. But it's an extremely expressive instrument, with a huge dynamic range - it really does entertain an audience. It's a wonderful feeling when you play it, really therapeutic."
As she points out, the composers who produced the greatest works in the clarinet repertoire were all inspired by particular players they knew - Brahms by Richard Mhlfeld, Weber by Heinrich Baermann, and Mozart by Anton Stadler. So she needs to find her own personal Mozart? "Maybe." She turns the question round. "Who do you think it might be? Who really speaks to you?" Silence. So much for the present lot.
She's not impressed by American minimalists like John Adams and Michael Torke - "They're OK, I suppose, if you are on drugs and sitting in a darkened room" - and she's admirably forthright on the limitations of the serialists. "From Webern onwards, you have to listen as a primary school child might listen. You have to absorb sound effects, rather than a coherent argument in a language you can understand." Touch.
Her latest notion is a collaboration with Kate Bush, but meanwhile she's busy expanding the clarinet repertoire by transcribing, and transposing, classical works originally written for the violin, viola, and French horn. As she points out, the clarinet is a very egalitarian instrument, versatile and relatively cheap.
Johnson does a lot of concerts for charity, notably for hospices. She gives master-classes all round the world, and, as a beneficiary of primary school music lessons, takes a strong line on the present government's contempt for such things. Chamber music is a growing interest: she often plays with the Guildhall String Ensemble, in which her boyfriend is a bassist. They don't use a conductor: as lead musician, Johnson also in effect conducts. Yes, she enjoys that role. "I couldn't lead the country, but I do have strong ideas about music."
Let's hope they're strong enough to resist any more pressure from the image-makers. After all, trendy gear and fancy hair-dos may do wonders for record sales in the short term, but they can only ever be a distraction from genuine music-making - as Nigel Kennedy learnt to his cost, driven into early retirement at the age of only 36.
n Emma Johnson gives the world premiere of John Dankworth's Concerto with the LPO at the RFH, South Bank, London SE1 (0171-928 8800) on Friday
Her new CD, the complete works for clarinet by Sir Malcolm Arnold, is on the ASV labelReuse content