But back to the Strad. I had heard all the stories: how the master used to roam the forests of northern Italy and tap on certain trees and mark them for his future use, how he invented a magical varnish that no one can duplicate — the secret of his greatness.
Sturm laughed. "Well, I'm not sure he actually went around tapping trees, but a violin maker does examine the straightness of a tree and the soil around it: a slower-growing tree is better because it makes for a tighter grain. Now all you do is go to the lumberyard. But the wood needs to be aged, and it must be quartersawn."
That is, the log is sawed lengthwise in quarters, and the top, or belly, of the violin is fashioned by joining two of these wedge-shaped pieces. When a piece is looked at edge-on, the growth rings appear as straight parallel lines. This grain gives the wood maximum strength. Otherwise, under the 70 or 80 pounds of pressure from the stretched strings and the narrow bridge, it would buckle.
The violin's sound is made by drawing the bow across the taut strings. The sound travels down to the foot of the bridge, where it is transmitted to the entire top surface of the instrument, which vibrates.
There is another element here, the sound post. This is a pencil-thick stub of wood that stands between the top and back. "The sound post transmits the vibration to the back piece, amplifying the sound still further," said Sturm. "Without the sound post you'd lose a lot of power."
About varnish: put it on too thickly, make it too brittle, and it can kill the sound of a violin.
"You can take a badly made violin," Sturm contended, "and no varnish in the world will make it sound good. The varnish protects the instrument and helps retain its flexibility. Because we don't understand how Stradivari made his varnish or put it on, we like to think this is some magic that explains the great tone. But there's the selection of the woods, the volume of air inside the violin, the flexibility of the wood itself," Sturm maintained.
One reason why a good old violin is generally preferred to a good new violin is that the wood changes over the years. The resins in wood gradually dry out, leaving the pores, the cellular structure of the wood, open. This makes the wood more flexible, so that it vibrates more easily.
"A friend showed me some wood from the German forest, a small strip of it planed in 1970, and another one from the same forest that was 200 years old. The new one was stiff as a two-by-four; the old one could bend like a playing card. That's the difference: the old instruments respond more quickly, it's easier to make the sounds," Sturm explained.
In his 93 years, Stradivari produced 1,100 instruments, of which 600 survive. "Stradivari's violins changed around 1700, when his golden period began," Sturm said. "They got much more powerful — here's why." He showed me how the belly of the older instrument arched more in the middle; the newer one was visibly flatter by maybe as much as a half-inch. This flatter shape generally creates a louder tone that can hold its own in modern concert halls. In Stradivari's time, music was played in small chambers, and it was not until the 19th century that music was written for larger orchestras in public theaters. By the 1890s, his violins were in great demand.