Many years ago, a talented make-up artist called Greg Cannom was talking to various producers about working on The Curious Case Of Benjamin Button and Watchmen. Film technology had not reached a sufficiently advanced stage at that time, however, and both projects were put on hold.

Fast forward 20 years and Cannom is a double Oscar winner. He has worked on both films back-to-back, realising a long-held dream to work on highly stylised stories that push boundaries in a craft he has fine-tuned for almost 30 years. Yet his experience on the films could not be more different. Watchmen, he says, was the most fun he has ever had on a production. By contrast The Curious Case Of Benjamin Button was arduous and often "terrifying" - yet Cannom believes it represents the finest work of his career.

This is saying something from the man regarded as the greatest ageing make-up specialist working today; Cannom is renowned for an uncanny ability to make actors look old. The way he slides Cate Blanchett and Brad Pitt towards and away from old age in David Fincher's The Curious Case Of Benjamin Button, inspired by F Scott Fitzgerald's romantic short story about a man who ages backwards, is extraordinary.

"Benjamin was very difficult," Cannom says from the Burbank-based Drac Studios he runs with two partners. "I was on it for 18 months. I've worked with Fincher before and knew it would be tough because Fincher wants it done right. But he pulls out the best in me. Most directors don't know how to shoot good make-up and effects. Fincher knows. When they asked me to do it, I knew it was going to be incredible."

He signed up and conducted two weeks of tests at Drac before the cameras rolled in New Orleans in October 2006. He spent six months in the Deep South, working on the younger Blanchett and Pitt characters. A year had passed by the time the production moved to the Paramount lot in Los Angeles to shoot the scenes where Blanchett's character is an old woman, recounting the story from her hospital bed.

"By the time I got to that part, I had to remember what I'd done before," says Cannom, a veteran of 150 films including Titanic, The Mask, Hannibal and The Insider. "It took four hours a day to put all the make-up on Cate, including 14 appliances (chin, cheeks, neck, eye bags, ear lobes, top lip, etc). After that first day Fincher came up to me and said, 'I want it like this every day for two weeks.' It was terrifying getting up every day and hoping it worked."

Cannom and his team of assistants transformed Blanchett into an 85-year-old woman whose life is gently slipping away. "Cate is such a professional and never once complained, but this was the hardest make-up I've ever done, because she's so beautiful and her skin is so smooth. I tried doing a typical age make-up on her and it didn't work because she has these incredible cheekbones. With most people you can build up the cheekbones, but with her I had to work around them and show the age down the neck and other parts of her face."

Cannom made head casts and worked with his colleague Miles Teves to create sculptures of the actors' heads. They used these to test appliances before handing over to the digital-effects teams for their requirements. Cannom uses Stipple, an old-age latex that is deliberately stretched on to the skin so it creates wrinkles when released.

"You can age someone 10 years that way," he says. "I used it on Gloria Stuart in Titanic." Cannom's assistant would splatter age spots on to the face, neck and hands with tattoo brushes before he went in and painted individual spots onto the make-up.

The breakthrough came when Cannom combined paper-thin acrylic transfers on Blanchett's forehead with silicone. Most make-up artists use foam for forehead make-up and as far as Cannom knows his technique on Benjamin Button was unprecedented. It was so realistic that, when they took Blanchett in full make-up to meet her Indiana Jones And The Kingdom Of The Crystal Skull director Steven Spielberg on an adjacent sound stage, the director had no idea who she was. "He shook her hand and thought it was an old woman who'd won a competition."

Cannom appears to be a shoo-in for the make-up Academy Award, but even though he has shared Oscars before for Mrs Doubtfire and Bram Stoker's Dracula and collected a technical achievement Oscar in 2005, he is not complacent. "I still want to do the perfect make-up, and this isn't it. It's close to it and I'm really happy with it, but it's not the perfect make-up." Perhaps he will achieve that level on his next project, Mannerheim, a biopic about the Finnish president and soldier who ages from 20 to 84 in the script. Cannom still hungers for the next challenge. "I've gathered all this knowledge but there's not much time left in which to use it."