During the late 1940s, Copland became aware that Stravinsky and other fellow composers had begun to study Arnold Schoenberg's use of twelve-tone (serial) techniques. After he had been exposed to the works of French composer Pierre Boulez, he incorporated serial techniques into his "Piano Quartet" (1950), "Piano Fantasy" (1957), "Connotations" for orchestra (1961) and "Inscape" for orchestra (1967). Unlike Schoenberg, Copland used his tone rows in much the same fashion as his tonal material—as sources for melodies and harmonies, rather than as complete statements in their own right, except for crucial events from a structural point of view. From the 1960s onward, Copland's activities turned more from composing to conducting. He became a frequent guest conductor of orchestras in the U.S. and the UK and made a series of recordings of his music, primarily for Columbia Records.