Beyond their sound, though, the old instruments encapsulate history, passing through the hands of the world’s great performers. The history of the Greenhouse cello has been traced to 1816 and Vincenzo Merighi, the son of a violin maker who played in La Scala’s orchestra, becoming its principal cellist in 1823. Merighi later played quartets with Paganini, who bought the cello for his collection. The collection was consigned by his son, Achille Paganini, to a Paris luthier named Jean-Baptiste Vuillaume in 1846.

Count Louis Charles Georges Corneille de Stainlein-Saalenstein, an amateur musician and a host of musicales, appears to have acquired the cello in 1854, and it then passed to the Countess of Stainlein. After her death in 1908, Paul Grummer, a future cellist in the famed Busch Quartet, took possession. A collector in Aachen, Dr. George Talbot, bought the cello from Grummer in 1938. Nineteen years later, Greenhouse heard about the instrument and tracked it down. “I opened the cello case and fell immediately in love,” he says in Delbanco’s book. “The color of the varnish, the shape of the instrument, it was so beautiful, so very beautiful, and it seemed to me a great jewel.” He paid what his daughter Elena described as a fortune for the time, although a tiny fraction of what it’s worth today.

Through the optic of history, those in possession of these instruments are caretakers, not owners. For their players, the transfer to the next caretaker symbolizes the end of performing, the termination of an artistic prime, the memories of which reside in long-used instruments. “The violin is not only a friend,” said Aaron Rosand, 84, once a prominent soloist in the tradition of the great Romantics like Oistrakh, Milstein and Heifetz. “It’s something that you live with. Every day it becomes more dear to you. It’s almost like a living thing. You treat it carefully; you treat it gently. It talks to you,” he said. “You’re caressing your instrument all the time. Parting with an instrument that has become such a wonderful friend is just like losing a member of your family.”

In 2007, Rosand announced that he planned to sell his Guarneri del Gesu, the Kochanski, and donate $1.5 million of the proceeds to the Curtis Institute of Music, where he studied and continues to teach. He recently had back surgery and could no longer stand long enough to perform. “It didn’t make any sense to tie it up,” he said. Over the next couple of years, Rosand received offers, including some from noted players who came to try it out. “I could hardly bear to hear it played by someone else,” he said. But their offers were not large enough. “I wasn’t going to part with it just for admiration for someone’s fiddle playing. Once I decided to sell it, I wanted to get the price for it.”

Then he received a visit from a man he described as a Russian oligarch. Working through the dealer Peter Biddulph, Rosand flew to London with the Kochanski and checked into a suite at the Langham Hotel one day in October 2009. He resisted any urge to play it one last time. “I didn’t have the heart to,” he said. The next day, Biddulph and the Russian arrived at the suite. The mood was somber as the dealer examined the violin. They spent three or four hours in the suite, waiting for e-mail confirmation from Rosand’s bank that the money had gone through. They ordered tea and filled the time with small talk about the violin’s travels and Rosand’s concert tour in the old Soviet Union. When the e-mail arrived, the Russians left, and Biddulph took the instrument to his vault. The price, according to Rosand, was $10.1 million.

“It’s hard to completely express what it meant to me,” Rosand told me last month when I spoke with him about letting his instrument go. “The agony, the tears I shed on just thinking about the parting.” He made good on his pledge to Curtis, paid $2 million in taxes and is using some of the rest to help with his grandchildren’s educations and to give to charity. He said he talked to the buyer about having other violinists use the instrument, but he received no assurances and does not know if it remains in a vault or under a violinist’s chin.