There are perhaps no instruments more legendary than violins made in Cremona, Italy during the 17th and 18th centuries.

Antonio Stradivari and other Cremonese luthiers from this period developed and used techniques in their instruments that many still consider to be the best in the world. A Cremonese violin is assembled by hand from more than 70 different molded pieces of wood.

Stradivari produced an estimated 960 violins during his life in the late 1600s and early 1700s. Around 500 of his violins have survived. They sell for as much as $16 million today. 

What's made them especially iconic is that modern makers have struggled to create replicas that measure up.

"Despite tremendous advances in sciences and arts since the industrial revolution, violin making represents a singular case that has undergone a functional decline," says Hwan-Ching Tai, who led a team of researchers to figure out why this is.

Tai's team looked at samples of wood taken during restoration work, including instruments by Stradivari, Nicolò Amati and Guarneri ‘del Gesù’.

In analyzing the spruce of a 1740 violin from Guarneri ‘del Gesù’, the team discovered large traces of aluminum (1300 ppm), while Amati and Stradivari samples were below 50 ppm. 

"This is best explained by chemical experiments involving family recipes, instead of buying pre-treated wood from lumber suppliers or random contaminations from later centuries," the team wrote.

The research found that Stradivari used salt seasoning in his violins. For alkaline treatment, Stradivari used potash and Guarneri used lime. 

Researchers also found some evidence of altered cellulose nanostructures. 

"For the first time, solid evidence has been gathered to validate the hypothesis that soundboard materials used by Stradivari and Guarneri differ significantly from the unprocessed spruce preferred by modern makers."

"Chemical treatments performed by Stradivari and Guarneri changed how wood fiber molecules are arranged and bonded together. This should lay to rest any claim that Cremonese masters did not possess closely guarded manufacturing secrets," the team concluded.

If you're interested in diving deeper into the science, check out the full research article here: https://onlinelibrary.wiley.com/doi/10.1002/anie.202105252