Daylight saving time had been in effect only a few hours last November when New York City Ballet principal Sterling Hyltin entered an NYCB rehearsal studio to recapture history. In Classroom 2 on the seventh floor, the clock had been turned back to 1968, when NYCB premiered Balanchine's La Source, a demanding pas de deux with four solos set to a Léo Delibes score and made on Violette Verdy and John Prinz. The George Balanchine Foundation, which is dedicated to preserving the choreographer's ballets in a state as close to the original as possible, had arranged to tape Hyltin and Gonzalo Garcia in practice clothes performing La Source.

Verdy herself was there as an expert observer and advisor, while Helgi Tomasson, who often performed La Source at New York City Ballet before becoming artistic director of San Francisco Ballet, served as co-critic. Lined up along one mirrored wall of the classroom were an accompanist at a grand piano, a movie cameraman, sound technicians and an assistant responsible for keeping a boom mike hovering out of camera range to catch every word Verdy and Tomasson said to Hyltin and Garcia.

Choosing Hyltin for taping this demanding role would have surprised no one who saw her debut in La Source the last week of the 2010 spring season. She had only one opportunity to achieve its many piquant subtleties, such as the brace of gargouillades that blossom amid a flourish of footwork, and she performed each with the assurance and precision of a veteran. “NYCB ballet master Sally Leland invited me to observe the company rehearse the three casts," Verdy recalls. “Sterling was incredible, with endless arms and legs, and she was always open to criticism. Her dancing has a quality I call 'true from the inside.' "