How an object becomes priceless.

The 'Baron von der Leyen' Stradivarius of 1705

Auction, Strings Attached

Antonio Stradivari left few traces when he died rich and respected in 1737. Even his birth date is guesswork. But what mattered most was already clear to contemporaries. Stradivari's violins were so good that fake Strads soon began appearing on the market.

On April 26, Tarisio, a young New York firm, will put the 1705 Baron von der Leyen, one of about 500 to 600 surviving Stradivari violins, up for auction online. It last changed hands in 1969, when six-digit prices were still over the horizon. Prices now begin at seven: The von der Leyen is expected to sell for $2.5 million to $6 million.

Tarisio

The Baron von der Leyen Stradivarius is expected to sell for $2.5million to $6 million.

For more than 300 years, Strad prices have been a leading indicator of Western culture. On the eve of the 20th century, eyes rolled when Strad prices in pounds reached five digits. Two world wars cooled demand. But the curve again turned north as Europe recovered and Asia joined the game.

In 1971, a Singapore developer broke $200,000. In 2006, Jerry Kohl, a California businessman, bought the great Nathan Milstein's Strad for $8 million. Last June, the 1721 Lady Blunt, as upper-end as Strads get, went for $15.9 million.

"There are no bad Strads, just as there's no bad Mozart," says Hellmut Stern, a veteran of the Berlin Philharmonic. "But not all Strads are equal."

He could be talking about the Baron von der Leyen, named for its first known owner, a German silk merchant. In 1969, it went to Harold Kohon, a respected New York session player, with an affinity for contemporary music and modern jazz. Mr. Kohon died last year.

The next owner is unlikely to be American or a player. These days Americans are likelier to sell. Players borrow Strads from people who can afford them.

But customers should be no problem, despite a history of restorations and a recent blind test demonstrating that neither players nor listeners could tell a Strad from a good modern instrument. "It will take many more scientific studies and a lot more time to sway violinists and collectors," says Phil Margolis, creator of cozio.com, the violin world's go-to database. "Apples and oranges," says Jason Price, Tarisio's chief executive.

Meanwhile, a shocked Roger Hargrave, one of the most admired living violin makers, reports that a fake Hargrave recently sold on eBay. It's news that a midrange Strad is now expected to sell for more than what an upper-end Strad fetched just a few years ago. The first hint yet that a living violin maker is also believed to be worth faking is news, too.