The whiteness of stonepaste provided a canvas upon which potters could paint pigments directly, rather than applying a slip. By the early thirteenth century, a new type emerged, decorated in black and blue against the white ground, usually with vegetal motifs inside radial frameworks. The stable black pigment creates crisp outlines and fine details, while the rather runny blue fills contours and highlights forms. Underglaze painting would have long‑term consequences on the development of Iranian ceramics.