Violins and Alchemy

Depiction of Stradivari in his workshop

Stradivari. Guarneri. Are these names familiar to you? They probably aren’t unless you have a love of classical music or perhaps play a stringed instrument. Antonio Stradivari and Giuseppe Guarneri were two of the most famous Italian instrument makers of the 18^th century. The sound of their instruments has long been classified as rich and elegant, and many have tried and failed to match the quality instruments that these artists have made. 

Until recently, the top quality sound from these instruments has been believed to come from the type of wood used and the geometry in the instrument itself. However, recent studies have provided evidence for degradation in the wood due to microbes and other chemicals that changed the acoustics of the instruments.

In a 2009 study by a group at Texas A&M University, instruments made by Stradivari and Guarneri were compared to French and English instruments from the same time period as well as natural wood controls. The group had examined the same wood in 2006 and had come to the conclusion that the polymers in the wood had undergone degradation that is possible only through chemical means. They examined the wood using many methods of analysis, including back-scattered electron imaging, x-ray fluorescence, wavelength dispersive spectroscopy, x-ray spectroscopy, and quantitative microprobe analysis. Their findings support the idea that Stradivari and Guarneri knowingly or unknowingly used chemicals to treat the wood while making their instruments (budding chemists, maybe?). These compounds are speculated to reduce hemicellulose enzymes, which also reduce the moisture and the density of the wood. This turns out to be really important in a good-sounding instrument.
 

All four of the Stradivari and Guarneri instruments that were analyzed did contain unusual compounds compared to all of the other samples. The most noteworthy was the finding of sodium borate (borax), a common insecticide and fungicide that was used back in the day and still is today. Calcium fluoride and zirconium silicate (Zircon) were also found in some of the samples. None these compounds occur naturally in wood, so they must have been added by the makers themselves. Since the researchers took care to avoid varnish samples, these compounds were either unintended for the instruments or added deliberately. Cool thing is, the salts are known to cause atrophy of the wood and also help in oxidation. This leads to stiffness of the wood, an important factor in sound quality. 

In the 1800s, boiling the wood of instruments was common practice. This removed both tension and other soluble substances that clogged up the pores. The wood became stiffer and dryer, which led to better sound and higher sound velocity. However, this also had the potential to damage the instrument unless done properly.

Being soaked in water also helped the sound of the wood because the cell walls remain open, allowing the wood to retain some amount of permeability. The wood used for the instruments was most likely floated down-river, picking up microbes and bacteria along the way. These little organisms burrow into the wood, adding to the permeability as well. Scanning electron microscopy revealed remnants of fungi and bacteria, and the wood also had more holes in it than modern counterparts. Besides allowing for permeability, the holes create more room for the varnish to seep into the wood, which improves the vibrational qualities, depending on the composition of the varnish, of course.

The varnish itself was extremely important to the quality of the violin. Analysis revealed that the varnish in one of the Stradivari instruments was composed of calcite, quartz, feldspar, and gypsum. Garnet, rutile, and argentite were also present, along with fifteen other minerals. The hard varnish increases the acoustics of the walls of the instrument, and has the potential to reduce noise emission, depending on what type of crystals are used.

In the end, there is still room for research on why the Stradivari and Guarneri instruments are a cut above the rest. Like any other piece of art, scientists very rarely touch musical instruments like these, unless a nondestructive technique is used. It’s still a bit of a mystery, but we do know a good instrument comes from stiff, permeable wood and a strong varnish, as well as a little bit of chemistry.

Stradivarius Violin

Here's my dilemma. Were Stradivari and Guarneri geniuses who knew what they were putting on their instruments and why? Or did they just somehow luck into the circumstances of wood type and varnish that led to magnificent creations? Even with all of the chemical and physical evidence behind the instruments, people today still can't reproduce the amazing quality from these Italian artisans. And so, the mystery persists.

Resources:

http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0004245

http://www.nagyvaryviolins.com/the_chemistry_of_a_stradivarius.pdf

http://www.nature.com/nature/journal/v444/n7119/full/444565a.html