Of the 6 billion people on the planet, there are perhaps four men whose knowledge of rare violins is so vast and deep that their opinion of an antique instrument can set its market worth. Robert Bein, a Chicago dealer, is one of these four. Talk to him about the fiddles that he sells and his face grows as expressive as a stage actor's. He grimaces when considering a disagreeable point. He pauses for effect before delivering a punch line. And when he grows serious, he fixes his watery blue eyes on you and unloads the weight of his convictions. He thinks the old instruments are worth every penny. "Except for these fiddles, not one single object on this earth works better than it did 200 years ago," he says insistently. "Stradivari is the ultimate icon of Western civilization. I mean, what finer thing exists?"

As if to prove the point, Bein says, "Let's go see some Strads." We leave his office and its view of Lake Michigan and thread through a warren of rooms where several young violinists are filling the air with a jumble of scales. In a back corridor, we arrive at a seven-foot-high steel vault. Bein swings open the doors to reveal several levels of shelving, each level divided into 10 or so narrow, vertical compartments, each compartment covered in green felt and deep enough to hold a violin.

You know how it is: Someone hands you a $4.5 million violin, and you try not to drop it. Bein gives me a 1734 fiddle built by Giuseppe Guarneri del Gesu, and I turn it gingerly to look at the burnished back of flamed maple and the carved scroll above the tuning pegs. I rub my thumb across the strings. It makes a resonant, $4.5 million plonk.

Bein grabs it back and slides it into its slot in the vault. He hands me another. "This is a 1686 Stradivari called the Nachez." Like paintings or country estates, old violins have names. "This goes for $1.5 million," he says and pulls out two others. "This one is a Guadagnini that would go for $600,000 on a good day, and this is an...