>A recent paper published in the journal Analytical Chemistry reported that 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, and hence the resulting sound. Meanwhile, another paper published in the Journal of the Acoustical Society of America showed that the better resonance of older violins produces stronger combination tones, which can also affect the perception of musical tones. > >... > >It's the varnish that has received the most attention in recent years. The theory dates back to 2006 when Joseph Nagyvary, a professor emeritus of biochemistry at Texas A&M University, made headlines with a paper in Nature claiming that it was the chemicals used to treat the wood—not necessarily the wood itself—that was responsible for the unique sound of a Stradivarius violin. > >Specifically, it was salts of copper, iron, and chromium, all of which are excellent wood preservers but may also have altered the instruments' acoustical properties. He based his findings on studies using infrared and nuclear magnetic resonance spectroscopy to study the chemical properties of the backboards of several violins (the backboard is the instrument's largest resonant component). > >... > >While prior research largely focused on the chemistry of the varnishes, Chiaramaria Stani of the Central European Research Infrastructure Consortium (CERIC) and co-authors were keen to take a closer look at the treatments used before varnishing the instruments to fill the outer pores of the wood. It's a matter of considerable academic debate since some studies found just a layer of drying oil between the varnish and the wood. Other studies using chemical staining and gas chromatography showed the presence of proteins—most notably animal glue (collagen) found in two early 18th-century violoncellos, and casein found in a 1730 violin. Traces of unidentified proteins were also detected in violins from 1677, 1706, and 1720 using staining tests.

This looks to be some pretty interesting research on some of the other wood treatments that might have been used in the preparation of the wood before and during the construction of these instruments and ultimately may be of aid to future luthiers as they work to improve their processes.