Dose of fungus could make sweeter-sounding wood.
A dose of rot can make for a better-sounding violin, say Swiss researchers who have used fungal infections to change the acoustic properties of wood.
The treatments make the wood less dense, and have a similar effect to the cold climate that helped to give Antonio Stradivari’s instruments their legendary tone.
The Swiss team is now working with a luthier to produce six violins from three trees with fungally treated wood and three with untreated wood. The researchers will then have the violins played to experts in a blind test. The instruments should be finished by the end of this year.
The efficiency with which a vibrating piece of wood transmits sound waves into the air depends on the ratio between the speed at which the waves pass through the material, and on the density of the instrument. A high ratio makes for a louder instrument.
Stradivari had the good fortune to be working during the early eighteenth century. This was the coldest period of the Little Ice Age, when temperatures around 1 ºC cooler than today. Trees grow more slowly in cold climates, resulting in close-packed rings and less dense wood.
Sound usually travels more slowly through rotten wood; foresters exploit this property to diagnose infested trees. But in the 1990s, Francis Schwarze, who studies wood at the Swiss Federal Laboratories for Materials Testing and Research in St Gallen, discovered that a few species of fungi infect wood without causing this slowdown. The fungi degrade cell walls, but not the lignin tissue that makes wood woody.
A few years ago, a chance encounter with a luthier got Schwarze thinking that these fungi could offer instrument makers an opportunity.
Schwarze and his colleagues incubated samples of Norwegian spruce, used for the top plate of violins, with the fungus Physiporinus vitrius. And they incubated samples of sycamore, used for the instruments’ bottom, with the fungus Xylaria longipes.
After 20 weeks of incubation, the wood had reduced in density by more than 10%, and showed a concurrent increase in sound transmission, without its structure being significantly weakened. “The longer the incubation period, the more the acoustic properties improved,” says Schwarze. The team reports its results in New Phytologist1.
Wood treated with fungi also damps sound more efficiently, giving it a mellower timbre. “I think they will have a smoother sound,” says Martin Schleske, the Munich-based instrument maker who is collaborating with Schwarze. And treated wood looks better, he adds. “It has more of a golden colour, like a nice Italian instrument.”
“It’s a very interesting method, but it’s only a first step,” says Joseph Nagyvary, a chemist and luthier based in College Station, Texas. Nagyvary has worked on the possible chemical treatments used by Stradivari2 and has suggested that by soaking their wood in water, early luthiers encouraged microbial damage that made it easier for varnish to penetrate the wood.
But the wood samples used in the Swiss experiment are much thinner than the wood in instruments, he says, and it could be difficult to get the fungus to attack the wood evenly. It might be better to use fungal enzymes, rather than the fungi themselves, he suggests.
Chemical treatments have also been used to make wood for violins less dense, says Claire Barlow, a materials engineer at the University of Cambridge, UK. Such treatments might also have economic benefits, as wood that grows slowly is becoming more expensive and harder to find, thanks partly to global warming. “This may be a way to use cheaper wood,” she says.
But, Barlow points out, there's more to making a top-quality violin than just the condition of the wood. “It’s incredibly difficult to link the properties of wood to the sound that comes out of a violin,” she says.
Schwarze, F. W. M. R., Spycher, M. & Fink, S. N. Phytol. Avance online publication doi: 10.1111/j.1469-8137.2008.02524.x (2008).
Nagyvary, J., DiVerdi, J. A ., Owen, N. L. & Tolley, H. D. Nature 444, 565 (2006).
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Whitfield, J. Rot offers fresh sound for violin makers. Nature (2008). https://doi.org/10.1038/news.2008.894