Or perhaps it was the varnish Stradivari used: a cocktail of honey, egg whites, and gum arabic. A 2022 study involving nanoscale imaging of two such instruments revealed a protein-based layer at the interface of the wood and the varnish, which may influence the wood’s natural resonance.
Biochemist Joseph Nagyvary has argued that it was the chemicals used to treat the wood that give Stradivari violins their unique sound, specifically salts of copper, iron, and chromium used to preserve the wood—all of which are excellent wood preservers but may also have altered the instruments’ acoustical properties. A 2021 study supported that argument, identifying borax, zinc, copper, alum, and lime water as the most likely chemicals affecting the sound.
CT scans have provided quite a bit of insight into the conundrum, since the technique can reveal wood density, size and shapes, volume measurements, and thickness graduation, as well as any damage or repairs to a given instrument. For instance, a 2009 study used CT scans to study the material properties of the wood. In 2011, Minnesota radiologist Steven Sirr took detailed CT scans of the 1704 “Betts” violin and then collaborated with two luthiers to make a replica.
One of the most thorough investigations was the Strad3D project, spearheaded in 2006 by the late George Bissinger. That project used 3D scanning lasers to make detailed quantitative measurements of the acoustic properties of several Stradivarius violins, essentially mapping out precisely how the instruments vibrate and hence produce their distinctive sound. (For what it’s worth, when I interviewed Bissinger way back in 2007, he was skeptical of efforts to one day reproduce the sound quality of a Stradivarius violin on a mass scale, insisting that making an instrument is as much art as science and that there is no single secret to the Stradivari sound.)