After several years of singing operetta and light opera in Norway, Flagstad was persuaded to take on heavier, dramatic roles, including those of Verdi and eventually Wagner. Working on the role of Isolde in particular, for a production in Oslo in 1932, seems to have irreversibly changed her voice, increasing her power and stamina. On the recommendation of Ella Gulbranson, a Norwegian singer who had appeared at the Bayreuth Festival, Winifred Wagner invited Flagstad to audition for the Festival. In her first season there she sang the minor roles of Ortlinde and Third Norn and the following year Sieglinde.
The Bayreuth performances also produced an invitation to appear at the Metropolitan where she made her debut as Sieglinde in Die Walküre. Virtually unknown outside of Scandinavia until she was nearly 40 years old (and considering retirement), Flagstad exploded upon the operatic firmament with that Metropolitan Opera debut, which just happened to be broadcast across the United States and Canada. Overnight she became the pre-eminent Wagnerian soprano of her generation—for some “the voice of the century.” She travelled to San Francisco later that year to sing all three of Wagner’s Brünnhildes for the first time, in the opera company’s first Ring.
In the next season, the San Francisco Opera succeeded in doing what the Metropolitan was never able to do: put the two leading Wagnerian sopranos of the time on stage at the same time. In two performances of Die Walküre, audiences in the War Memorial Opera House heard Flagstad as Brünnhilde and Lotte Lehmann as Sieglinde, with Fritz Reiner conducting, Lauritz Melchior as Siegmund, Emanuel List as Hunding, and Friedrich Schorr as Wotan. Some private recordings of these performances (taken from 1936 radio broadcasts) reside in the Archive of Recorded Sound at Stanford University Library.
In 1940, with the outbreak of war and then the occupation of Norway, Flagstad wished to return home, to be with her husband, Henry Johansen. Her decision was natural but naive. Although she never sang for the German occupiers, there were those, both in Norway and elsewhere, who saw her return to her occupied homeland as a gift to the oppressors. At the liberation, Henry Johansen, although seriously ill, was arrested as a war profiteer (as were many businessmen who had supplied goods to the occupying forces) despite the fact that he had also helped the resistance. His death a year later was a serious blow to Kirsten. The post-war years were difficult for her, while her husband’s business and estate, including some of her own property and savings, were held by the state; and Flagstad was met with malicious newspaper articles and demonstrations wherever she performed.
In 1947-48 she undertook an extremely successful North America tour and returned to the San Francisco Opera in Tristan und Isolde and Die Walküre in the fall of 1949. She sang at Covent Garden in 1948-51, Paris Opéra as Isolde in 1948, Salzburg as Leonora in Fidelio in 1949-50, and at La Scala in 1950. She also performed at Chicago, Teatro Colón of Buenos Aires, and the Vienna State Opera. She resumed performing at the Metropolitan in 1950, giving her farewell performance on April 1, 1952 in the title role of Alceste (Glück).
Toward the end of her career, Flagstad gave mostly concert performances. She made a number of recordings of songs by Mahler, Grieg, Sibelius and others, and she took part in Bernard Miles’ Mermaid Theatre project, appearing there in the 1951 production of Purcell’s Dido and Aeneas which was subsequently revived in Oslo. She retired from the stage in 1955, but returned to London to give a concert of Grieg songs in 1957. In 1958 she was invited to become the first General Manager of the Norwegian National Opera, and she remained in that post until 1960.
Often hailed as one of the most beautiful voices of the 20th century, Flagstad’s voice was distinguished by its dark sound, full volume, aristocratic breadth and perfect singing technique. In later years Flagstad’s voice darkened and she lost some of her previously brilliant upper register. Several critics and opera mavens guessed (correctly) that some of Isolde’s high Cs in the 1952 Furtwängler (EMI) recording of Tristan und Isolde were furnished by Elizabeth Schwarzkopf.
Flagstad’s recordings range from the old acoustics to the modern tape-transfer (tweaked) technology. The recording here is on HMV (DB 2746) with Hans Lange as conductor.