As free jazz spread in the 1960s, so did the use of tone clusters. In comparison with what John Litweiler describes as Taylor's "endless forms and contrasts," the solos of Muhal Richard Abrams employ tone clusters in a similarly free, but more lyrical, flowing context. Guitarist Sonny Sharrock made them a central part of his improvisations; in Palmer's description, he executed "glass-shattering tone clusters that sounded like someone was ripping the pickups out of the guitar without having bothered to unplug it from its overdriven amplifier." Pianist Marilyn Crispell has been another major free jazz proponent of the tone cluster, frequently in collaboration with Anthony Braxton, who played with Abrams early in his career. Since the 1990s, Matthew Shipp has built on Taylor's innovations with the form. European free jazz pianists who have contributed to the development of the tone cluster palette include Gunter Hampel and Alexander von Schlippenbach.