Though much of his work was made public only years later, Charles Ives had been exploring the possibilities of the tone cluster—which he referred to as the "group chord"—for some time. In 1906–7, Ives composed his first mature piece to extensively feature tone clusters, "Scherzo: Over the Pavements". Orchestrated for a nine-piece ensemble, it includes both black- and white-note clusters for the piano. Revised in 1913, it would not be recorded and published until the 1950s and would have to wait until 1963 to receive its first public performance. During the same period that Ornstein was introducing tone clusters to the concert stage, Ives was developing a piece with what would become the most famous set of clusters: in the second movement, "Hawthorne," of the "Concord" Sonata ( 1904–15, publ. 1920, prem. 1928, rev. 1947), mammoth piano chords require a wooden bar almost fifteen inches long to play. The gentle clusters produced by the felt- or flannel-covered bar represent the sound of far-off church bells (). Later in the movement, there are a series of five-note diatonic clusters for the right hand. In his notes to the score, Ives indicates that "these group-chords...may, if the player feels like it, be hit with the clenched fist." Between 1911 and 1913, Ives also wrote ensemble pieces with tone clusters such as his Second String Quartet and the orchestral "Decoration Day" and "Fourth of July", though none of these would be publicly performed before the 1930s.