The JACK Quartet (Stephen Poff/Handout)

An important mission of the concert series at the Library of Congress is to commission and present new works of contemporary music. Both aspects of that role were showcased Friday night, as the JACK Quartet, leading specialists in new music, performed a program of music mostly from the last half-century, including two pieces commissioned by the Library of Congress.

The oldest music in the concert was composed by Morton Feldman, beginning with “Spring of Chosroes,” commissioned by the Library’s McKim Fund in 1977. Pianist Ursula Oppens premiered the work with its dedicatee, violinist Paul Zukofsky, and she performed it here with Ari Streisfeld, one of the JACK violinists. Like Feldman’s “Structures” for string quartet, from 1951, this is understated, heavily repetitive music, but it diverts rather than bores because Feldman introduces unexpected, minute variations into those repetitions. It did not hurt that the JACK Quartet played these pieces with such intensity and beauty of tone, even if for an inversely modest effect.

Oppens also gave the world premiere of Elliott Carter’s piano quintet at the Library of Congress in 1998, but here it was the JACK Quartet that stole the show, bringing out the fragile beauty of the work’s central slow movement, in which out of nowhere the viola has a couple of achingly beautiful solos. The piece was paired with “Exordium,” composed for string quartet by Brian Ferneyhough to mark Carter’s 100th birthday, a work of 43 ultra-compact sections almost impossible to unpack without studying the score.

Both the Ferneyhough piece and Julian Anderson’s first string quartet, “Light Music” (composed in the 1980s but not performed until recently), explored many extended techniques on the four string instruments, binding them into one multi-voiced instrument of many colors. The concert ended with another piano quintet, composed by Thomas Adés in 2000, distinguished on this program for its rhythmic vitality, melodic beauty and variation of texture.

Downey is a freelance writer.

Ursula Oppens (Christian Steiner/Handout)