Black Angels, for electric string quartet

Black Angels, subtitled "Thirteen Images from the Dark Land", is a work for "electric string quartet" by the American avant-garde composer George Crumb. It was composed over the course of a year and is dated "Friday the Thirteenth, March 1970 (in tempore belli)" as written on the score. The Latin phrase in tempore belli, in time of war, written into the score by Crumb is a reference to the Vietnam War taking place at the time when Black Angels was composed. Crumb numerically structured the piece around 13 and 7, as numbers traditionally related to fate and destiny. The piece is notable for its unconventional instrumentation, which calls for electric string instruments, crystal glasses, and two tam-tams. The work quotes a portion of the second movement, Andante con moto, from Schubert's String Quartet No. 14.