Tony Foster recalls the day he nearly died for his art. “I realised something was wrong when I started coughing up blood. My body was swollen all over and I knew I was in trouble.”

Foster was working at an altitude of 17,600ft on a watercolour of Everest. “It nearly killed me,” he says, matter-of-factly. “I told my Sherpas that I had to go down. We descended to 14,500ft where I was treated by a doctor. I remember saying to him that I'd thought a good night's sleep would have sorted me out. He said that if I had stayed at over 17,000ft for any longer I wouldn't have lasted another night.”

The 61-year-old had acute mountain sickness, pulmonary oedema and cerebral oedema. Cortisone and oxygen helped lessen the effects of high altitude, as did a spell in an inflatable pressure bag used to treat severe altitude sickness. “Yes, painting Everest nearly killed me,” he agrees.

The myth of the suffering artist is normally associated with mental anguish rather than physical trauma. But for Foster, who lives near Fowey in Cornwall, the latter comes with the territory. His willingness to endure discomfort in the creation of bold and dramatic watercolours has made him a highly collectible artist in America, while remaining little known in Britain. This could be about to change with the publication of Painting at the Edge of the World, a book documenting his 25-year career.

“I think American people see something of the classic British adventurer in me,” Foster says. A “blend of eccentricity and lunatic endeavour” has stood him in good stead.

Foster is a former art school teacher who quit at the age of 35. “I decided to get out into the world,” he says. And he has done just that. As well as Everest, he has painted the Grand Canyon, the Costa Rican rainforest, volcanoes in Hawaii, Bolivia and Montserrat and, as a genteel contrast, Thoreau's country in New England. He has also notched up some remarkable records.

“I think I'm the only person to have painted all three sides of Everest, which is basically a triangular mountain,” Foster says. He believes he has also created the largest painting of Everest ever done on site (6ft by 3ft) and says that so far, no one has challenged his claim to have created the highest painting - 17,800ft up - on Kala Pattar looking east to Everest. Foster downplays the records as much as the derring-do, but it is impossible not to wonder what drives him - and, indeed, to question how it is possible to paint in such extreme conditions. He is happier discussing the practicalities than analysing his motivation. “Sherpas will help carry equipment and usually a number of friends accompany me - explorers, mountaineers, geologists, botanists and scientists. They give me a lot of support and do their own thing, though the primary purpose of the trip is always painting.”

But doesn't paint go solid? “Yes,” Foster says, “but if you mix gin with the paint water, you stop it freezing.” Bottles of Gordon's Gin duly accompany him on Everest trips, though rum is the artist's tipple of choice: “I take a 151-proof bottle of rum with me. It's got a kick like a mule, makes for less weight and mixes well with anything, especially chocolate.”

What about painting in extreme conditions - how does he keep warm? Foster says he has a mug of hot tea every two hours, and then looks slightly quizzical. “I wear a down glove on my left hand and paint with my right, but don't wear anything on it. People have often asked why my exposed fingers don't get frostbite. The truth is, I don't know. I can paint for six to eight hours on Everest in minus 5C but for some reason I've never had a problem with my hands.” He has, though, been caught in a blizzard - “It was grim, we were holed up for days on end” - and admits that the success of his expeditions, which are funded by sales of his work, entails a large dose of “willpower and determination”. No wonder: his drawing board often has to be lashed to rocks to secure it against gale-force winds.

Foster's holistic approach to landscape is evident in the way he annotates his paintings with soil, rock samples and stones or, in the case of some of the Everest paintings, Tibetan prayer flags. “I'm often at a place for weeks at a time and I like to tell the story of my work. The Tibetan prayer flag is wrapped in a Chinese newspaper to symbolise China's suppression of the Buddhist religion. Elsewhere, I incorporate souvenirs, geological artefacts and diary entries.”

One story, though, will not be told on canvas. On a trip to Death Valley, Foster came even closer to death than on Everest. “I had to come to terms with the fact that I might not survive,” he says, and for once, his equanimity appears to falter. It soon recovers when he is asked why he does it. “Good question. If I knew the answer I'd probably stop.”

Searching for a Bigger Subject, Royal Cornwall Museum, Truro, until April 26 then Royal Watercolour Society, London SE1, from July 2; Painting at the Edge of the World

(University of Washington Press, £39.95), www.tony-foster.co.uk

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