History is revealed in tree rings. They have been used to determine the ages of historical buildings as well as when Vikings first arrived in the Americas. Now, tree rings have shed light on a longstanding mystery in the rarefied world of multimillion-dollar musical instruments. By analyzing the wood of two 17th-century stringed instruments, a team of researchers has uncovered evidence of how Antonio Stradivari might have honed his craft, developing the skills used in the creation of the rare, namesake Stradivarius violins. Mauro Bernabei, a dendrochronologist at the Italian National Research Council in San Michele all’Adige, and his colleagues published their results last month, and their findings are consistent with the young Stradivari apprenticing with Nicola Amati. A Stradivarius violin currently on the auction block — the first such sale in decades — is predicted to fetch up to $20 million. [to access the full story a NYT subscription may be required]