ARTS / Master of antiquities, master of ceremonies: Collectors don't usually appear until opening night, to clink a glass or two at the private view. But when George Ortiz loans his collection to a museum, he moves in.

George Ortiz is the owner of the finest collection of antiquities in private hands. He's been collecting for nearly 50 years, but when talking about one of his pieces he behaves like a small boy with a new toy, bouncing up and down with excitement. Standing in front of a marble head of a boy, in the same breath that he tells you its date and origin (Constantinople, around AD 375), enthuses about the finely chiselled features and assesses the boy's character. 'He's a spoilt brat . . . In the Imperial court, he gets away with anything. He's not a pleasant person,' he says with such certainty, he must have known him. Describing one of the most striking pieces in his collection, a bronze image of Ajax dating from around the 1st century BC, he says 'he is vibrating, pulsating, a miracle . . .'

Ortiz's collection spans 30 cultures and virtually the entire history of art in the ancient world, from the Neolithic age to the late Byzantine period. Some 300 treasures from his 1,000-strong collection are on loan to the Royal Academy from tomorrow, following their display in Russia last year.

Most collectors, having lent their treasures to public exhibitions, do little more than turn up to the opening-night reception. Not Ortiz. Ortiz the Collector becomes Ortiz the Curator: for the past fortnight, working late into the night, the Royal Academy of Arts in London has become a home from his Geneva home. Staff at the RA are more or less leaving him to it. Ortiz's knowledge of his subject is almost unrivalled. His eye for spotting museum-quality objects is legendary. It was not until Ortiz acquired his collection of Egyptian bronzes that their importance was recognised: as Eleni Vassilika, keeper of antiquities at the Fitzwilliam Museum in Cambridge, recalls, 'Scholars were unaware that there were Middle Kingdom bronzes on this scale before Ortiz bought them.'

Watching Ortiz at work, you realise that the exhibition's title, 'In Pursuit of the Absolute', says as much about the collector as the craftsmanship within the collection. In the months before the show, he made himself a scale plan of the RA galleries, and mapped out exactly where everything would go. The model - the size of a 12-seater dining-table - came with him to London where it looks like a war game, and Ortiz its general. A design team was employed, but everything in this show has the Ortiz touch. Not only did he write the catalogue, but he designed everything from the display-cases to the packing-cases. He's almost as proud of them as their contents. He insisted that the display-cases be made according to the height of the objects to be placed inside them and not to some uniform height - something that frustrates him about other shows. To light the pieces he flew over Rusty Culp, senior designer from the Freer Gallery of Art in Washington. As the RA could not afford state-of-the art lighting, he bought them some.

GEORGE ORTIZ was born in Paris in 1927 into the Bolivian Patino tin-mining family. His father, Jorge Ortiz-Linares, a Bolivian diplomat of aristocratic Spanish descent, was listed as one of the world's richest men in the Forties. In 1952, after the Communist revolution, the Patino mining interests and land in Bolivia were expropriated. Ortiz says his own fortune is almost entirely in his collection.

And, he adds, he has had to make sacrifices. The Ferrari, for a start. 'For somebody born financially very privileged,' he says, 'and who used to race when he was young . . . his life's dream was having a Ferrari . . . I've never had the Ferrari, as each time in my life - the moment I was about to have one - some wretched object came up]' The moment he falls in love with a piece, that is it. He waited 20 years until a collector would part with the 'Bull-man' - a Sumerian mythological creature carved in alabaster in the 3rd millennium BC.

Ortiz began collecting as an adolescent. 'I was looking for God, for the truth and for the absolute,' he recalls. 'In 1949, I went to Greece and I found my answer.' In its art, he found 'a spirit' which he was much later to perceive was 'the spiritual birth of man'. As he explains, 'possibly I instinctively hoped that by acquiring ancient Greek objects, I would acquire the spirit behind them'.

Until then, he had not studied art. 'My approach was purely intuitive, instinctive. The vision of certain objects struck me viscerally . . . I let them speak to me, I let their content and spirit nourish me. I learnt by looking, by feeling, and then reading the labels and comparing.' And that, he says, is how everyone should approach them. One of his first buys was a Neolithic heavily rotund female idol (in the show). 'She moved me when I first saw her, and, amazingly, when I looked at her in moments of anguish or doubt these disappeared . . . In her time, she was an idol of fertility, a protection against the fates . . . What is it in this idol that alleviated the anguish of Neolithic man and mine?'

ORTIZ bought his antiquities from leading dealers and auctioneers worldwide. But provenance is a touchy subject in this field. Lord Renfrew, professor of archaeology at Cambridge University, appeared on The Late Show last night arguing his view that 'a really reputable national organisation like the Royal Academy ought not to be putting on an exhibition where one can make the inference that objects have come from illicit excavations'. He does not finger any particular piece in the Ortiz collection but says that anything acquired on the market in recent years, or catalogued as 'provenance unknown', is likely to have a murky past.

Ortiz is a past master at fending off the objections of a small number of archaeologists. His conscience is clean. 'I would not collect if I thought what I was doing was either immoral or amoral. Eighty per cent of all the works with supposed 'illegal provenance' are chance finds. The more we have restrictive laws, the more people will hide the provenance. Some of these remains are the roots of humanity and therefore should belong to humanity.'

20 Jan-6 Apr; pounds 4.50 (pounds 3 concs) (071-439 7438)

(Photograph omitted)