Varnish protects violins while making them look pretty, but it also affects the way they sound, a new study suggests.
In a paper published in Applied Physics A, researchers from Switzerland and Germany used X-ray imaging and vibration tests to measure the thickness, penetration into the wood and chemical composition of four varnishes – two produced in the lab and two used by German master violin makers.
They found the German varnishes produced a louder, richer sound than the lab-made coatings.
The soundboard of a violin – the upper face of the instrument's body, sitting beneath the strings – is usually made of spruce tonewood and is coated in liquid varnish which, once set hard, protects the wood from humidity and wear.
Marjan Gilani from the Swiss Federal Laboratories for Material Science and Technology and colleagues wondered if that varnish might affect the instrument's sound. After all, when a bow is dragged over a violin's strings, vibrations travel from the strings down through the bridge over which they're stretched, to the soundboard. The soundboard transmits the vibrations to the surrounding air, which become sound waves.
So Gilani took specimens of wood cut from the same Norway spruce tree and applied the lab-made and master makers' varnishes to them.
They checked the thickness of the varnishes, as well as how much they soaked into the wood, during the hardening process.
All coatings penetrated approximately 100 microns into the wood, with exception of a laboratory varnish, which had the highest proportion of oil and soaked deeper.
They all also "damped" the wood, meaning they helped vibrations be absorbed and stopped faster. A bit of damping is a good thing in a violin. High notes sound warmer and more mellow.
But the German masters' varnishes dried thinner than the lab-made coatings. This damped the wood both with the grain and across it – more so than the laboratory varnishes.
This leads to louder, more evenly radiated sound from the instruments.
So if you have a violin that needs revarnishing, your best bet is with the master crafters.
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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