John Richardson has devoted more than a decade to Picasso: A Life, the book that has simultaneously made and enslaved him. It's a biography in the Proustian vein, a loving remembrance of what the cicadas sounded like on a particular morning when Picasso fed the birds in his studio before beginning to paint a portrait of a new lover. The difference being that, while Proust retreated to his cork-walled room to write about his own fictionalised memories, Richardson is attempting a recollection of someone else's life.
He hasn't exactly been living in a cork-walled room either. Since the publication of Picasso: A Life, volumes one (1991) and two (1996), Richardson, who was in his late 60s when the first book appeared, has become a full-blown literary celebrity. He has been in a Gap ad, and claims that a friend was so astonished to see him on the side of a bus that he crashed his car. He has published a memoir of his relationship with art collector Douglas Cooper, The Sorcerer's Apprentice, and writes for Vanity Fair - he says that this is how he's funding Picasso. On the cover of the new book he's promoting, a collection of essays entitled Sacred Monsters, Sacred Masters, the blurb promises that "Richardson comes out from under the shadow of Picasso".
And yet when he talks, that shadow just gets longer and larger, until it seems as if Picasso could be in the room, gazing from the corner with what Richardson calls his mirada fuerte , his strong Andalusian look. Although he's now researching the third volume of Picasso: A Life, I expected to have trouble getting Richardson on to the artist. But once he starts, it's hard to stop him.
The new book - which to Richardson's fans can be no more than an ice cream between acts - consists of articles on artists and art-world hangers-on. They have a delicious poise, at once intellectual and cruel. Some have said bitchy. "I have a failing, but my failing is not being bitchy," says Richardson. "I'm censorious."
Perhaps the bile that he pours on modern art's secondary characters is a way of releasing a nastiness that he doesn't want to infect his great work. What distinguishes Richardson's Picasso from the hack biographies with their mean little "revelations" is that Richardson loves his subject. Loves him, champions him, and wants above all else to do him justice. Richardson knew Picasso when he was young and the artist was old. He and Douglas Cooper gave Picasso's last lover, Jacqueline Roque, a Dior wrap during the early days of her relationship with the artist, while Picasso's other friends scorned her. When she became Picasso's wife and gatekeeper they were rewarded for their kindness (or foresight). Richardson lunched with Picasso, and was a regular at his studio. What drives Richardson's vast book is a desire to bring to life the man he knew. And yet he finds himself embattled, as if to revere the artist were controversial.
"People move in on Picasso and have their own agenda. He was a wife beater and, OK, so everything else is subordinated to that. But whatever you say, the reverse is also true. He was also unbelievably tender, compassionate and loving. He was immensely wise, often rather childish. You can't just say one thing without always allowing for the other side of the coin."
On the table is a book by Picasso's granddaughter, Marina. "She is entitled to put her case, and I don't think she overstates it, but I wish that she would stop going on, because this is the second book. I would have thought she had got it all off her chest." What Marina needs to get off her chest is painful enough; Richardson tells the story in Sacred Monsters, Sacred Masters. Marina's brother, Pablito, drank bleach the day after his grandfather's funeral; Jacqueline had banned him from seeing Picasso. Pablito took three months to die.
The roots of Pablito's brutally short life go back to the years that Richardson is researching for the third volume of Picasso: A Life, taking us from 1917 to Guernica. He and his collaborator Marilyn McCully have just found a cache of documents on Picasso's two-month visit to London in 1919 (he stayed at the Savoy and was a society sensation). He happily disgorges some of his discoveries.
Picasso gave Marina and Pablito the cold shoulder because they were his grandchildren with his first wife, Olga. "Olga has always been rather roughly treated by biographers," says Richardson, "and so I thought, well, I'd like to see her in a new and more positive light. And the more I dug away - we dug up some stuff in Russia - the more everything confirmed that she's much, much worse than I'd ever imagined." Picasso met Olga Kokhlova in 1917 when she was dancing with the Ballets Russes in Parade, the modernist ballet that he created with Jean Cocteau and Erik Satie. For the man who had spent his formative years in Montmartre, Olga represented a new world of high society. Their marriage was to break up over the next decade as Picasso became disgusted with the very values that had attracted him to her.
"People really couldn't stand her, because she took herself so seriously," says Richardson. "It was Madame Picasso coming into the room, you know, and Picasso was so unlike that, and never gave himself airs. He was incredibly generous with himself, his time, and his work - as long as he was in a good mood. And then here was this la-di-dah lady with airs and graces, who wasn't as grand as she claimed to be. Picasso used to say that he got so bored with Olga's gentility, with the nice little dinners served by a butler in white gloves, and with the car, the driver, the dancing teacher, fencing master and skating teacher for the son, that he stuck up on his front door a notice saying, 'Je ne suis pas un gentleman'."
By the mid-1920s they lived on separate floors of their Paris apartment. Picasso's art from this era is at its most fierce and unpredictable, as if he was changing mood daily. He was attracted both to classical art - he was fascinated by Poussin and Ingres, and the wealthy society that celebrated these old masters - and to the surrealists, with their belief that art must be made by the unconscious. "Beauty must be convulsive or it will not be," said Picasso's ardent surrealist fan, André Breton.
And there are few paintings that are as convulsive as Picasso's from the 1920s. One of these, The Three Dancers (1925), touches on a violent love triangle of three old friends, an ecstatic dance of death set in the south of France in the roaring 20s.
"That's such a complicated painting," says Richardson. "I got into trouble for saying the woman on the left is doing the Charleston, but she so obviously is doing the Charleston. There are so many things in there - his feelings about women, about his old friends. It's painted at the time when he's fed up with Olga, so it's about his rather violent feelings towards women, about his need for them and his lust for them."
Richardson means that Picasso was doing more than expressing his dislike of Olga in this painting; he was doing something more raw, delirious. Having seen Picasso up close, Richardson believes that art for him was a form of magic. "A lot of his work is rather like a witch doctor's fetishes. He could seduce through his work, get rid of a girl through his work, cast spells with his work." So when Picasso made a savage painting like The Three Dancers, it was a malediction, a curse.
Picasso is an artist who demands biography because his art is instrumental to his life. "Jacqueline was ill a lot," says Richardson, "and Picasso would say, 'You see I'm a prophet. I did that drawing of Jacqueline, with a fever chart all over the back and then, in black ink wash, a drawing of her looking rather sick. I think there was this aspect within him, this magical, witch doctor, shamanistic thing."
Richardson is in Picasso's thrall, whatever his publishers say. He has bound his life to Picasso's Life. It has given him acclaim, but in return the spirit of Picasso demands two more volumes, several years more writing and research. There are more than 50 years of Picasso's life and art (he died in 1973) to encompass in the two remaining volumes. Richardson will be 78 next February. "I didn't realise it was going to take over the whole of the latter part of my life, and that I was going to be doing nothing much else. But as I get older, it's what keeps me going, it gives me a raison d'être. Thank God for it. I'm going to survive because I've got to finish the book."
· Sacred Monsters, Sacred Masters by John Richardson is published by Jonathan Cape, price £20.