Neither piece, however, felt fully digested - which was anything but the case with the first half's Beethoven Cello Sonata in G minor (Op. 5 No. 2) and the Britten Cello Sonata in C (Op. 65).
The two are hard to discuss separately. Both Beethoven and Britten were in states of high metamorphosis: The former was a young composer departing decisively but carefully from the lingua franca of his day, while the latter, in middle age, was seeking what would be his more austere late style.
In the Beethoven (which is weighted more toward pianist than cellist), Barnatan projected much of the novelty that 18th-century audiences must have felt, with key and register changes ambushing you from the side door. That quality became the key to Britten's work: Though its compositional floor plan is traditional, you kept hearing certain patterns familiar from his past works being fearlessly splintered, scattered, and transformed.
The atmospheric sensuality of Britten's great opera Peter Grimes is far away in this 1961 Cello Sonata. Though cellist Mstislav Rostropovich's technical prowess had an impact on the pieces written for him, Britten gave him greater comprehension challenges, not unlike the intriguingly veiled manner of Shostakovich, though with less irony and dark humor to keep the listener hooked.
The Weilerstein/Barnatan performance turned a bright light on every moment of the ultra-serious piece, especially revealing Britten's staggering ingenuity. You could still wonder about the music's message (or messages, since it's dense) but do so knowing that the performers had thoroughly come to terms with the piece on every possible level.
With so little sense of falling back on received wisdom, the Beethoven and Britten performances felt like premieres, which made other parts of the concert suffer in comparison. Weilerstein's use of vibrato felt indiscriminate in the Rachmaninoff, which isn't like her, or in keeping with European trends that question the presence of vibrato in most any repertoire. In the Stravinsky, Barnatan was merely charming.
With luck, Beethoven and Britten will be part of Weilerstein's new recording agreement with Decca. Isn't it nice to know that performances by her and Barnatan need not live only in one's memory?
Contact music critic David Patrick Stearns at dstearns@phillynews.com.