Having been fascinated by British traditional slipware published in Charles J. Lomax Quaint Old English Potter in 1912, Leach explored old, lost slipware techniques. This particular decoration was made with an historic technique called "feathering". Leach and Hamada successfully revived it in the 1920s after discovering its method when spreading blueberry jam and cornish cream on toast.
A similar example is in the collection of Tate Britain, www. tate.org.uk/art, number T12063