How Tree Rings Can Encode a Violin's Age and Place of Origin
(Inside Science) -- A stringed instrument holds many clues about when and where it might have been made. The wear on the body, the opacity of the wood and the type of varnish used, for example, can all hint at its origin. In recent decades, a technique called dendrochronology, which dates an instrument using the tree rings on its body, has gained popularity.
This process can provide an additional way to identify if a violin might have been built by one of the famed 16th- or 17th-century luthiers in Cremona, Italy, such as Antonio Stradivari, or if it was built more recently and therefore probably worth significantly less money.
"Dendrochronology is a really important and kind of revolutionary technology," said Kevin Kelly, a violin-maker in Boston, Massachusetts. "Before [dendrochronology], there was really no scientific way to tell the age of something for violin-makers."
Scientists have traditionally studied tree rings -- the circular patterns found in tree trunks -- to learn more about Earth's past and present climate, the history of fires and volcanic eruptions, and archaeological ruins. But more recently, researchers have found new objects to investigate with this method, including stringed instruments.
Tree rings are nature's historians
Trees grow larger cells with thinner cell walls early in the growing season, and smaller cells with thicker cell walls later in the growing season, explained Paolo Cherubini, a senior scientist at the Swiss Federal Institute for Forest, Snow and Landscape Research. These early-season cells appear lighter in color, creating alternating light and dark rings, with each pair marking a year of growth.
The properties of these rings, such as their widths, are influenced by environmental factors such as temperature and rainfall. Trees that grow near each other, and are exposed to the same conditions, should have similar looking rings each year. Scientists can use that information to estimate where and when the wood used to make an instrument grew by matching the tree ring patterns found on the instrument to those of trees and other instruments from an established time and place.
When Paul Sheppard, a dendrochronologist at the University of Arizona, in Tucson, dates violins, he starts by looking at the instrument under a microscope and marking off sets of 10 rings with sticky notes, which won't damage the instrument. Then, he measures the width of each ring.
"The craftsmanship of the violin-makers is so extraordinary that … it's pretty easy to count the rings and see them," said Sheppard.
He enters these widths in a computer, which compares the data to a vast record of measured widths spanning hundreds of years. If there's a particularly high correlation between the instrument's ring widths and another record, those two sets of tree rings might represent the same years in history and a similar geographic origin.
Limitations with dendrochronology
Cherubini, who wrote about tree-ring dating of stringed instruments in the journal Science last week, cautioned that this methodology "cannot tell you when the instrument was crafted," only the earliest possible year the instrument could have been built. Sometimes, instrument-makers would cut off the newest part of the wood, or they would store the wood for a while before making an instrument. So the instrument might have been made some time after the date of the outermost ring that's visible on the violin.
And dendrochronology doesn't always lead to a match, said Sheppard. "To cross-date two samples together, you need a certain amount of time, a number of years [of tree rings]," he said. Small stringed instruments, like violins, might only have 60 years of growth represented on the top of the instrument. And it can be difficult to detect a match if there isn't much variability between each ring. For an instrument with little variability and few rings, "I'd say the chances of dating that violin are almost zero," said Sheppard.
It can also be difficult to get accurate measurements "if the varnish is dark, the rings are very narrow, [or] the instrument is damaged," Katarina Čufar, a dendrochronologist at the University of Ljubljana in Slovenia who has dated stringed instruments, said via email.
Cherubini would also like to see more tree-ring data collected. "That means taking living trees, but also beams from churches and houses," he said, to build chronologies from places "where we think the wood [for instruments] was coming from."
Combining dendrochronology with other tools
Dendrochronology is a rigorous approach to dating instruments, but more traditional techniques and other technological advancements are still valuable tools. Kelly, the violin-maker, said that "you can tell a lot about an instrument's age just by looking at it." For example, he said, as wood gets older, it gets less transparent, and light shines through the instrument's body less easily.
Sheppard sometimes takes violins he's dating to a maker, who examines the instrument's length, curvature, color and other stylistic features. "He would get a pretty solid impression of any violin I showed him pretty quickly," Sheppard said. "Most violins, you can tell it came from a certain region at a certain time, because you've seen a hundred other ones just like it," Kelly explained.
Cherubini said when a date from tree-ring pattern is combined with other characteristics, like the shape of the instrument and its varnish, and other methods like carbon dating, you can get "much more confidence in your dating."