Tide purl is the most recent and shortest of Liz Johnson's works for string quartet and the simplest in its concept. Inspired by the play of light on sand as river water flowed onto the beach one evening at Druidstone in Pembrokeshire, the music builds out from and back to the single pitch D, exploring the patterns created by using intervals of a third fanning out from that point. This starting and returning to the same pitch is a musical device she draws on in other compositions on the album, Intricate Web.