The last self-portrait by Anthony van Dyck doubled its estimate to set an artist auction record at Sotheby’s in London as buyers fought for the best work and rejected other paintings.

The event totaled a mid-estimate 15.1 million pounds ($24.6 million), including fees, with 42 percent of the 50 offered lots failing to sell.

Collectors are being selective as auction estimates for a diminishing supply of Old Masters have shown little change over the last 12 months, said dealers. Valuations for the rarest works have increased, they said. This contrasts with estimates for contemporary art, which have been slashed by as much as 50 percent after the financial crisis.

“It’s a beautiful painting,” the Van Dyck’s joint buyer Alfred Bader said in an interview after paying 8.3 million pounds. “And it’s for sale.” Bader, a veteran Milwaukee-based art investor, was buying in partnership with the London-based dealer Philip Mould. They beat eight other bidders, said Sotheby’s.

The oval-shaped canvas, showing the head and shoulders of the Antwerp-born painter dressed in a black and white silk doublet, had a 3-million-pound upper estimate. It had been executed in London in 1640, the year before Van Dyck’s death, and had been in the family collection of the Earls of Jersey since the 18th century. The paintings was one of only three self- portraits the artist produced in England, said Sotheby’s.