Alkaline-glazed ware and its moulds

For all their variety, the glazed wares of Nishapur in the ninth and tenth centuries shared two things: a body of natural clay and a glaze high in lead; then, sometime after the close of the Samanid period at the end of the tenth century, a new ware began to be made, different in body, glaze and prevailing colour, as Wilkinson explains. ¹

The new body was white, gritty and hard, composed mostly of silica as finely ground quartz with perhaps a little clay; its whiteness let potters paint designs directly on it, rarely needing an engobe. ¹ It suited thin-walled moulded vessels, which became very popular, and it suited the new glaze, fluxed with alkali rather than lead: an alkaline glaze does not fit natural clay, but on the gritty body it penetrated and fused so that it did not spall. ¹

Wilkinson distinguishes them: clear lead glazes have a delicate soap-bubble iridescence, alkaline glazes a partly opaque iridescence and often a pitted surface, and when thick a fat, soapy look associated with borax. ¹ He notes that Abu al-Qasim Abd Allah listed borax in 1301 among the materials of the Kashan potters, and that because alkaline glaze ingredients dissolve in water they were first fritted into a glass and then ground. ¹

The characteristic alkaline-glaze colours at Nishapur were light blue, by far the commonest, from the copper that gives green with lead — more intense at Nishapur than at Rayy; then dark blue from cobalt, never before used at Nishapur; less often purple, and a colourless glaze; Nishapur made no green alkaline glaze. ¹ The excavations found kilns at Qanat Tepe that produced this ware. ²