According to musicians, the violins of Antonio Stradivari, who lived from 1644 to 1737, produce music with a level of purity unmatched by modern instruments. The mysterious finish applied by the master hundreds of years ago gives them a unique look and sound.

What is the secret of Stradivari violins?

Researchers in analytical chemistry have obtained a nanometer image of the coating on two Stradivari violins. They discovered another protein-based layer between wood and varnish. Previous studies have also shown that some string instruments created by Stradivari have a hidden layer under the glossy varnish. Its purpose was to fill and even remove wood, which affects resonance and sound. Knowing the components of this layer is the key to playing these instruments in modern times.

• The authors of the study used two precious violins – “San Lorenzo” from 1718 and “Toscano” from 1690.
• Using synchrotron Fourier transform infrared spectroscopy, the team found that both samples had an interlayer, but this method was unable to determine the composition of the layer.
• The scientists then turned to the near-field infrared scattering scanning microscope (IR s-SNOM).
• The IR s-SNOM instrument includes a microscope that collects images tens of nanometers wide and measures infrared light scattered from the layer to gather information about the chemical composition.
• The results of the new method showed that The layer between the wood and varnish of both tools contains protein-based compounds that combine into nano-sized dots. Mostly, amide proteins were found, which are formed when carboxylic acids are heated with ammonia. The compounds are also actively used in modern industry: to increase the elasticity of paper and artificial leather for the production of paints and polymers.

“San Lorenzo” and “Toscano” violins / Photograph by Chiaramaria Stani et al./Analytical Chemistry, 2022

Because IR s-SNOM provides a detailed three-dimensional picture of the types of matter on the surface of the violin, the researchers say it could be used in future studies to identify compounds in complex, multilayered samples from other cultural heritages.