THE familiar platinum blonde hair is artfully tousled, the black liner around the provocative blue eyes is millimetre perfect. In a break between filming scenes for The Misfits, the last film she completed, Marilyn Monroe is standing about with a crowd of extras, drinking coffee and chatting animatedly.

At another point she's having her hair done; a few moments later she's seen with one of her co-stars, Clark Gable, who was to die after a heart attack within weeks of the end of filming in the baking Nevada heat. Some said it was the stress of working with the spoiled and unpredictable Marilyn that precipitated his end.

This behind-the-scenes footage is a silent movie, despite the fact that the two cans of celluloid were shot in 1961.

But even without sound, the 8mm treasure trove that's been kept under wraps for 47 years, practically burns with the intensity of Marilyn Monroe's sex appeal. No breathy little-girl voice, no cutesy songs or even a pucker of the lips are necessary.

Whatever you want to call the thing she had, she clearly had it when simply standing still or sipping from an enamel mug, doing nothing to wilfully provoke the adoring gaze of the lens or the onlooker. She simply had to be.

Since Monroe was found dead at her California home in August, 1962, at the age of 36, every aspect of her life, loves and films has been scrutinised. Many of her belongings have been sold and resold. It seems that there's little about her that has not been wrung dry of content and meaning.

No actress has had more words written about her, more pictures published, more song lyrics composed, more artistic homage paid – from Andy Warhol to Madonna to Elton John to Kylie Minogue – cultural icons who have fed off what the screen siren represented. For some it was the sheer glamour and sex she exuded; for others it was her aura of bruised vulnerability.

When it came to light that two rolls of film existed which had not been publicly viewed and pored over, naturally fireworks went up in the world of Marilyn watchers. Initial estimates put the expected starting bids at between $10,000 to $20,000, but by the time the hammer came down, the price had reached $60,000 (£30,000).

The 47-minute film, On the Set with The Misfits, was shot by film extra Stanley Floyd Kilarr.

The film shows actors preparing for scenes, chatting with crew members and others on the set, and relaxing between takes.

Cathy and Rod McCormick, of Sparks, Nevada, obtained the film canister from her father, Frank Hasy, Kilarr's uncle.

Small snatches of the film were aired on the internet and in TV news programmes to whet the appetite of bidders.

Such is the demand for Monroe-abilia that an umbrella once used by the star changed hands for $42,000 some years back.

The Lemon Marilyn, one of 13 pop-art portraits of the actress made in different colours by Andy Warhol, was auctioned for $16.2m a few years ago, and another sold for $15m.

The dress Monroe wore when she sang Happy Birthday Mr President to JFK (one of her paramours) shortly before her death sold for $1.26m.

Why is so much made of the remnants of the life of a woman whose acting talent has been so questioned? Her beauty and sexual allure have never been in doubt, but were they enough to cause such lasting influence on the world of art and collectables as well as in the hearts of her legions of fans?

"There are screen acting legends like Errol Flynn, Gary Cooper and Ingrid Bergman, and there are icons like James Dean and Marilyn Monroe," says Tony Earnshaw, head of film programming at the National Media Museum in Bradford. "There is so much worship of her that anything she touched is going to make headlines.

"The fanaticism that follows her is what I'd call fetishistic. Her allure for those millions of fans is not just about what she did in her relatively few films but the fact that she was both manipulated and a manipulator and that, having died at 36, she remains forever young – like James Dean.

"Her appeal also has to do with her image, which was part sex symbol and part gaucheness and naivete, summed up in a way by the scene in The Seven Year Itch where her dress blows up. Her character is doing it for fun and because the air cools her down; but anyone watching finds it very sexy."

Despite glimpses of terrific comic talent in films like Some Like It Hot Monroe was, by the late 1950s, typecast as a blonde bimbo. She studied method acting and got married, for the third time, to Arthur Miller, the writer with a planet-sized brain. He wrote the art house movie The Misfits, but by the time it came to be shot by John Houston the marriage was on the rocks.

Laurence Olivier, who had worked on The Prince and the Showgirl with Monroe, called her a "brilliant comedienne, which to me means she is also an extremely skilled actress..."

He said that even though she drove him to distraction with her lateness and drug-dependency. Others are still not so convinced by Marilyn.

"Marilyn had been told she was deluding herself if she thought she could move from lightweight to serious actress," says Tony Earnshaw.

"Her attempts were hampered by the influence of Paula Strasberg, the method acting coach who filled her head with all sorts of ideas about changing herself. It meant she agonised over everything and couldn't get through a scene. She had also left it too late to decide she no longer wanted to be an air-head."

Monroe's powder compacts and gladrags may fetch millions, but her abilities are still very much up for debate. "She's a star, not an actress. If she'd listened to the right people and not been in search of self-confidence through sleeping with men she might have been better," added Mr Earnshaw.