varnish that was introduced when European chemical supplies were cut off. This resulted in problems with surface noise even on new records, and Edison's market share shrank. Prior to the war Edison Records started a marketing campaign, hiring prominent singers and vaudeville performers to perform alongside and alternating with Edison records of their performances played on top-of-the-line "Laboratory Model" Edison Diamond Disc Phonographs. At various stages during the performances, all lights in the theater would be darkened and the audience challenged to guess if what they were hearing was live or recorded; accounts often said that much of the audience was astonished when the lights went back up to reveal only the Edison Phonograph on stage. According to a book published by the Edison company titled Composers and Artists whose Art is Re-Created by Edison's New Art (ca. 1920), the first such comparison test or "tone test" as Edison copywriters referred to them, took place at Carnegie Hall on April 28, 1916 with Marie Rappold of the Metropolitan Opera providing the live vocal performance. After the war, disc quality improved substantially as better quality ingredients became available again, and in the brief postwar boom Edison regained status in the industry. Sales for Edison discs peaked in 1920, but declined incrementally thereafter. In 1926, an attempt at reviving interest in the Edison Disc was with a 450-GPI long-playing disc, acoustically recorded and still spinning at 80 rpm, with times of 24 minutes per 10-inch disc and 40 for a 12-inch disc, but problems occurred (notably with broken groove walls and overall low volume, often only 40% of that of the regular discs), and the disc failed. In August 1927, discs began to be electrically recorded, making Edison the last major label to adopt electrical recording (over two years after Victor, Columbia, and Brunswick had converted from acoustical recording). Concurrently, Edison tried to freshen its catalogues by recording popular dance bands such as those of B. A. Rolfe and Harry Reser (whose "Six Jumping Jacks" group appeared on Edison as "Earl Oliver's Jazz Babies"), the Goldman Band conducted by founder Edwin Franko Goldman, jazz performers Eva Taylor and Clarence Williams, and radio personalities like Vaughn De Leath and "The Radio Franks" (Frank Bessinger and Frank Wright). Classical performers who became Edison artists in the late 1920s included pianists E. Robert Schmitz and Moriz Rosenthal, violinists Arcadie Birkenholz and Erna Rubinstein, the Roth