The sweet, rich sound of Stradivarius violins enable them to fetch millions of dollars. For years violin aficionados have debated why the instruments made by Stradivari and his contemporary Guarneri sound so beautiful. Researchers have pored over their geometry and acoustics, but a new study concludes that chemistry makes the difference.

"This answers the centuries-old question if Stradivari and Guarneri used wood that was natural or chemically treated," says Joseph Nagyvary, a biochemist at Texas A&M University. "The answer is, very clearly, chemically treated."

For over 20 years, Nagyvary, who also taps his research to create violins, collected wood shavings from the interiors of Stradivari and Guarneri instruments when they came in for crack repair and restoration. Nagyvary targeted the deep inner layers from the interior of the instruments. "We don't damage violins but use something that restorers already have in their shops," he says.

Using spectroscopy on the wood scrapings, Nagyvary and his colleagues found how the violins produced by these Italian artisans differed from antique French and English instruments as well as those made with modern woods. The Stradivarian wood, the researchers report in this week's issue of Nature, had been treated with chemicals that oxidized and hydrolyzed it. One previous suggestion was that Stradivarius and Guarneri had treated their instruments with potassium silicate, or water glass. But the researchers found no trace of this compound, and the oxidizing and hydrolyzing agents that were used is not yet known.

This treatment may have preserved the wood and improved the violin's sound. Soaking the wood, as Stradivari did, diminished the violin's excess low noises, Nagyvary explains. But this was only part of the equation that gave these violins their characteristic tone. Varnish, which Nagyvary has previously analyzed, adds acoustic brilliance. "Both of them are material aspects of violin making," he says. "Materials science emerges as a tool for making the best violins." And Nagyvary hopes modern violin makers, like himself, will take notice and come up with their own magic formula.