Hockney paints a birthday reunion

The artist (left), 60 in July, is marking the occasion by showing portraits of his family and friends which must be sold together. Ros Wynne- Jones discovers why

David Hockney is selling his mother. But if you want to buy her, whether it's the portrait where her startlingly youthful blue eyes match her sweater, or the one where she looks all of her 96 years, there is a catch. You'll have to buy the whole family - and his friends, and his housekeeper, and her daughter - at a cost of around pounds 750,000. Where one portrait goes, the other 23 in the set follow, by the artist's strict instruction.

The portraits are showing in London from Thursday; the most important people in Hockney's life appearing together at the Annely Juda gallery as they do in his mind's eye, until his 60th birthday on 19 July.

The exhibition is entitled Flowers, Faces and Spaces although Hockney toyed with the more anarchic Fuck You, they're all Flowers and Portraits. Much has been made of the flower pictures, inspired by a visit to the Vermeer exhibition at The Hague last year, but the portraits, all painted in the past six months, reached London only last week. The most recent, of the housekeeper's daughter, Dayanna Fernandez, was finished less than a month ago. Less still has been made of the spaces, within which lie the key to the artist's desire that the portraits be sold together. "When you put the portraits together they work as an installation," says David Juda. "It is as much about the spaces between the portraits and in the background colour as it is about the faces."

None of the portraits is framed, appearing as if they were on the wall of Hockney's studio or sitting-room. Each is the size of a cornflake packet and their vibrant colours, influenced by Hockney's realisation that the brilliance of Vermeer's 17th-century palette would outlast Hollywood's, are repeated throughout so that the eyes of his friend and printmaker Maurice Payne, for example, have their reflection in the background of the portrait of his ex-lover and manager Gregory Evans.

Some of the subjects have sat for him hundreds of times from when he was a small boy with a set of crayons. The pictures gathered together, as perhaps the subjects will be on his 60th birthday when the exhibition ends, include two of his brothers, John and Paul, his sister Margaret and her partner, his friends Driffen and Don Cribb, and Jonathan Silver, curator of the David Hockney museum in Salts Mill, near Bradford, who bought his first Hockney aged 13 for pounds 2 from the teenage artist.

"He's nearly reached 60, three-score years, and you look at life very carefully when you're 60," says Mr Silver. "He wanted to have his friends around him and then together in a collection for posterity."

Anne Graves, whose face appears in vivid red and purple among the new portraits, says: "I have sat for David many times since I met him in my teens, but these portraits have a very different, psychological quality. Sitting for David is a very intense experience. You have to allow your face to relax because you sit for such a long time not daring to move, and that means things show in your face.

"It's different for all of us now - we've had marriages and bereavements and divorces and as David paints, making little noises that tell you whether it's going well or not, you know he sees all that."

The only words Hockney has permitted in the portraits catalogue are a simple statement: "If you don't know them, you don't know enough about them to paint them." His friends say his portraits of them show he sometimes knows them better than they know themselves.