Un article passionant du New York Time nous raconte comment un chimiste taiwanais, Hwan-Ching Tai a découvert que ce sont les traitements minéraux spécifiques du bois des Stradivarius et autres Guarneri qui font leur qualité acoustique unique, ainsi que leur utilisation intensive depuis le 18esiècle. L’article est en anglais :

In the violin-making world, two names reign above all others: Antonio Stradivari and Giuseppe Guarneri.

Both masters lived during the late 17th and early 18th centuries, in a small town in northern Italy called Cremona, and garnered a reputation for making the best stringed instruments in the world. Since then, luthiers have tirelessly tried to imitate Stradivari’s and Guarneri’s craftsmanship, copying their wood choice, geometry and construction methods. But their efforts have met with little success.

For hundreds of years, the best violin players have almost unanimously said they prefer a Stradivari or a Guarneri instrument.

Why nobody has been able to replicate that sound remains one of the most enduring mysteries of instrument building. A new study, published on Monday in the Proceedings of the National Academy of Sciences, suggests that answers may lie in the wood: Mineral treatments, followed by centuries of aging and transformation from playing, might give these instruments unique tonal qualities.

“If you compare Stradivari’s maple with modern, high-quality maple wood that is almost the same, the two woods are very different,” said Hwan-Ching Tai, a professor of chemistry at National Taiwan University and an author of the paper.

In the study, done in collaboration with the Chimei Museum in Taiwan, Dr. Tai and his colleagues used five analytical techniques to assess wood shavings from two Stradivari violins, two Stradivari cellos and one Guarneri violin. Their measurements yielded several major findings.

First, they found evidence of chemical treatments containing aluminum, calcium, copper and other elements — a practice lost to later generations of violin makers.

The original neck of the 1725 Stradivarius violin nicknamed “Brancaccio.” Credit Chimei Museum

“Modern luthiers don’t do this,” said Henri Grissino-Mayer, a geography professor at the University of Tennessee, Knoxville, who studies tree rings and did not participate in this research. “This paper is the first to convince me that some type of mineral infusion into wood might cause superior sound in a musical instrument.”

It is unknown whether the tonal results of these treatments were coincidence, or whether the Cremonese masters knew beforehand that the chemicals would have an effect, Dr. Tai said. He said he thought the chemicals were probably first applied by forest workers who soaked wood in minerals to ward off fungus and worms before sale. Over time, the salts may have hardened the wood through chemical bonds.

The researchers also discovered that one-third of a wood component known as hemicellulose had decomposed in Stradivari and Guarneri’s instruments. Because hemicellulose naturally absorbs a lot of moisture, the effect was that the instruments had about 25 percent less water in them than more recent models.

“This is fundamentally important because the less moisture, the more brilliant the sound,” said Joseph Nagyvary, a luthier and a professor emeritus of biochemistry at Texas A&M University who was not involved in this study.

In comparison with other violins, Stradivari and Guarneri instruments are known for possessing rich, dark bass tones and a quality known as brilliance, or the ability to project a clean, high-frequency sound that “tickles your ear from far away,” Dr. Nagyvary said.

Dr. Tai’s team also found a property in the Stradivari violin samples but not the cellos: When they heated the wood shavings of the violins, they found an extra peak in oxidation, which implies a detachment between wood fibers.

This detachment, possibly the result of centuries of vibrations from playing, may give the instruments greater expressiveness, Dr. Tai said, adding, “Top violinists often feel like these old violins vibrate more freely, which allows them to express a wider set of emotions.”

Dr. Tai’s interest in Cremonese violins goes back a decade, to when he was a graduate student specializing in neuroscience at the California Institute of Technology. A friend told him about Dr. Nagyvary, who, in the 1980s, was the first to suggest that Stradivari and Guarneri had used chemically processed wood to make their instruments. Today, Dr. Tai’s lab focuses on the neurochemistry of Alzheimer’s disease, and he is still a hi-fi audio and classical music buff.

During the winter of 2006, Dr. Tai visited Dr. Nagyvary in Texas and got hooked on the mystery of the famed violins. He spent the next several years on a 60-page review of research on Cremonese violins.

Over the years, he said, many hypotheses about the secret properties of Stradivari and Guarneri instruments have come and gone.

For a while, people suggested that luthiers had simply used trees that have since gone extinct — but in fact those trees still exist. In 2003, Dr. Grissino-Mayer and a colleague said Stradivari’s secret had to do with the fact that he had lived during an extremely cold period, known as the little ice age, and that the trees around him were growing differently. How exactly that may have produced better instruments, however, remains unclear. Another popular theory — that Stradivari was using a varnish with magical sound properties — has not been substantiated by any chemical analyses.

Dr. Tai hopes that decoding the secrets in the wood of Cremonese violins will help guide attempts to build replicas that can preserve the sounds of Stradivari and Guarneri.

With their continued decomposition, many Stradivari and Guarneri instruments will lose their acoustics in the next 100 years, he said, adding, “These instruments will not last forever.”