Flowing colours are also referred to as "flow blue." This technique was associated with transfer printed patterns, although there have been a few examples of hand-painted wares using this technique. These designs are deliberately printed so that the pigment runs into the glaze, producing a blurred effect. Usually, these wares are produced using blue or purple pigments.
Also see Transfer Print
See Miller 1980:29, 1991: 9
Photo: Flow blue plate