The property mogul Aby Rosen had a birthday party last night. He’s a man with an eye, who owns a great many buildings, including those two thriving trophies of mid-century style, the Seagram Building and the Lever House. He also owns the mansion on 71st street recently vacated by the Salander O’Reilly gallery, who had failed to pay their rent since last October. Read about it by clicking here.

The gallery is no more, and while the mansion is on the market for $75 million, it seemed a good place to give a big party, something Rosen and his wife Samantha do with a reckless, generous flair. He knows that guests are best treated as greedy excited kids who want a multitude of treats. Vases everywhere overflowed with assorted candies, each room on three of the mansion’s floors had been turned into a separate VIP nightclub, with loud music, sofas, ottomans, champagne buckets, small tables full of glasses, bottles, cigarettes and ashtrays. The house is 45 feet wide, deep and high; hundreds of young blonds with pedigrees and their slightly disheveled dates milled between such sights as Dennis Basso the furrier, Vogue’s very tall Andre Leon Talley, Donald and Melania Trump and the billionaire David Koch. An almost equal number of waiters handed out truffled grilled-cheese sandwiches, mini burgers, sushi, skewers of beef, lamb chops to be eaten on the bone, tiny ramekins of macaroni and cheese, miniaturized cheesecakes and trays of profiteroles dripping with chocolate sauce.

Many of the guests had to leave early because they had, they said, “a ride to Cannes,” a seat on a private plane going overnight to the Cannes film festival. I wondered how many were on the same planes — and who might end up riding in the toilet.

Aby Rosen’s birthday falls right at the end of the spring contemporary art sales, so that the central hall of the mansion was filled with dealers flush with the thrill of commerce. This week, Christie’s sold $438.2 million worth of contemporary art on Tuesday, Sotheby’s tally was $362 million on Wednesday, and last night, Simon de Pury (whose small new auction house Phillips de Pury has been called, curiously, “boutique”) knocked down the gavel on $59 million worth of recent art. On Wednesday night, a Francis Bacon triptych had sold for $86.3 million.

In the front hall, the architect Richard Meier stood with Irving Blum, the legendary California art dealer, in the heady afterglow of all these sales. Irving Blum was dressed as if for a ball in tuxedo and bow tie; Meier was in a business suit. The host, just up the stairs, wore a black t-shirt with long sleeves. He usually entertains in Fruit of the Loom.

“You’re dressed up,” said Meier to Blum. “You must’ve made a lot of money tonight.”

“Ellsworth Kelly, 85,” said Blum, beaming.

“You just sold an Ellsworth Kelly for $85 million?” I asked.

Blum shook his head. “It was Ellsworth Kelly’s eighty-fifth birthday party.”