Bidders driven into frenzy by Old Masters : INTERNATIONAL ART MARKET

The oldest collection of Old Master paintings in America, 183 works donated to the New York Historical Society more than 100 years ago, caused a sensation when they came up for sale in New York last week.

The taste of the US connoisseurs who gave the paintings to the society was uneven, but the historical romance of the collection caused a frenzy of bidding, with more than 10 bidders sometimes after the same picture. The sale earned $12.2m (£7.8m) with only seven lots left unsold.

The society began its art collection before the Metropolitan Museum, but lost its way as an institution and is now on the edge of bankruptcy. A decision has been taken to sell non-American treasures and concentrate on the role of interpreting New York history.

The star turn was a 2ft (60cm) circular "birth tray" painted with The Triumph of Fame in 1449, by the Florentine artist known as "Lo Scheggia", to celebrate the birth of the most famous Medici art patron, Lorenzo the Magnificent. Sotheby's had valued it at $3m-$4m, but it was sold to the London dealer Rainer Zietz for $2.2m.

There was an obvious reason for the low price. The New York Attorney General had decreed that New York public institutions should have the right to pre-empt the purchase of any painting in the sale at the final bid price, provided they applied within seven days of the sale.

It was clear that the Metropolitan had its eyes on this extraordinary memento of the Florentine Renaissance and that discouraged bidders. It duly announced a pre-emption shortly after the sale. No other institutions have yet exercised their right, but they still have four days in which to do so.

The euphoria generated by the society auction rubbed off on the sale of Old Masters from other sources which followed. The most astonishing price was $552,500 for a 16th-century copy of Leonardo's Mona Lisa estimated at $80,000 to $120,000.

The painting was bought in France in the 1790s by William Henry Vernon, a collector from Newport, Rhode Island, and had descended in his family. There have been several attempts over the years to prove that it was painted by Leonardo himself before the Louvre picture. They have not been taken seriously by connoisseurs but were enough to spark competition between 10 private collectors at the sale.

Sotheby's other major auction of the week was devoted to the stock of London's leading sculpture and works-of-art dealer, Cyril Humphris, and proved something of a fiasco. After three decades selling works of art to the world's leading museums and collectors, Humphris had decided to sell up and start a new career in the theatre and movies.

Sotheby's offered 331 items from his business for sale, implausibly suggesting that they came from his private collection by dubbing the sale "The Cyril Humphris Collection". Sotheby's took a touring exhibition round the world and issued a stream of press releases in an attempt to pull in the bidders. In the event, none of the rarest lots sold and the auction made $6.6m, where Sotheby's had forecast $12m.

Many of the cheaper lots were allowed to sell at a fraction of the pre-sale estimates and the middle-market response to the sale was healthy. More people turned out to bid on Renaissance bronzes.