 His first chamber work, the string sextet Verklärte Nacht, was mostly a late German romantic work, though it was bold in its use of modulations.The first work that was frankly atonal was the second string quartet; the last movement of this quartet, which includes a soprano, has no key signature.Schoenberg further explored atonality with "Pierrot Lunaire", for singer, flute or piccolo, clarinet, violin, cello and piano.