A violin does not come with a passport. But the wood on its surface may still reveal exactly where it grew.
Scientists have used tree rings to trace the timber in hundreds of violins made by Antonio Stradivari, the Italian craftsman whose instruments are famous for their sound and workmanship. Their findings point to a forest in the Dolomite Mountains of northern Italy.
The discovery begins with the front of a violin.
Known as the soundboard, this thin wooden plate vibrates when the strings are played. Its stiffness, weight and consistency can affect how the instrument carries sound. Stradivari often made his soundboards from spruce, but historians did not know exactly where he obtained the trees.
Old stories offered several possibilities. One tale described a violin maker discovering perfect wood in an Italian mountain forest and persuading a builder to sell it to him. Similar stories appeared in other European countries, making the mystery even harder to solve.
The answer was hidden in a pattern of narrow lines.
A tree normally adds a growth ring each year. During a warm, favorable season, it may grow quickly and produce a wider ring. Colder or more difficult conditions often create narrower ones. Trees growing near one another experience similar weather, so their rings form matching sequences.
These patterns work a little like barcodes. Researchers can compare the rings in an unknown piece of wood with dated patterns from forests, old buildings and other wooden objects.
For the new analysis, scientists examined 314 ring patterns from 284 Stradivari violins. They compared the instruments with one another and with historical tree-ring records collected across Europe.
The results revealed a change in Stradivari's working habits.
Wood from his earlier instruments appeared to come from several parts of the Alps. During the period now considered the height of his career, however, he seems to have relied mainly on Norway spruce from Val di Fiemme, a forested valley in the Italian Dolomites.
In other words, the famous violin maker may have experimented with different sources before repeatedly returning to one place that produced wood he trusted.
Some violins had ring patterns so similar that their soundboards may have been cut from the same tree. Instruments carrying production dates many years apart sometimes shared this match. That suggests Stradivari may have bought excellent timber and stored it for future use rather than using it immediately.
The rings also revealed something about the forest itself. Many were unusually narrow, indicating that the spruce grew slowly in cold conditions at high altitude. Slow growth can produce wood that is dense and even, with fewer irregularities — qualities that may be valuable when making an instrument.
This does not mean cold weather alone created the celebrated Stradivarius sound. The shape of the violin, the thickness of its wooden plates, the varnish, the maker's skill and centuries of aging may all play a part. Scientists still debate how much each factor matters.
The forest identification also carries some uncertainty. Historical tree-ring records sometimes come from old buildings, and their wood may have been transported from another region before construction.
Even with those limits, the study adds a remarkable detail to the story of the instruments. Stradivari's workshop may have been in the Italian city of Cremona, but the sound began much earlier — inside spruce trees growing slowly on a cold mountainside.