|The development of stonepaste|
Early Islamic potters continued pre-Islamic pottery traditions and used low-fired earthenwares as their principle body-material. However, it seems that in the C9th, potters start to use a new kind of body-material called stonepaste (also known as fritware). This new type of ceramic body is known from dated pieces to have been produced in Iran from 1179 onwards (a bottle with lustre-decoration in the British Museum, Lane 1958, plate 52B), however recent scientific investigations into early Islamic pottery reveals that a proto-stonepaste is developed in Iraq in the C9th, and from there moves to Egypt where the technique is fully developed in Fatimid workshops, before moving to Iran. The explanation for the movement of this technology is probably that the potters themselves moved, taking their secrets with them.
Stonepaste consists of 10 parts ground quartz to 1 part glass inclusions (or frit) to 1 part fine white clay. This recipe is provided by Abul-Qasim of Kashan who wrote a treatise in 1301 with an appendix on pottery (see above, Section B; and Allan, 1973). The clay binds the material together, and reacts with the frit during firing to cement together the quartz grains. When fired, the material is hard, white and translucent, very like the fine Chinese porcelain that was being imported into the Islamic world at this time and which stimulated Islamic potters to innovate. (Go to section on Abbasid Ceramics: C8th-C10th) It is this stonepaste body which, together with a new tin-based glaze, revolutionizes the forms of Islamic pottery, and important types that use the new technology are lustre-wares and under-glaze painted pottery.
Mason has used a Scanning Electron Microscope to study sherds known from typological classification to be from C9th Iraq (Basra and Baghdad are the postulated production centres). His results reveal a large degree of experimentation in the body materials, the most significant being the sudden appearance of glassy inclusions in the normal clay body. It seems to be relict glass, ie. not a specially designed frit as in the mature stonepaste technology, but bits of glass leftover from the glass-making industry, which have been combined with the normal clay body. The effect of adding glass is to increase the vessels hardness and density by accelerating vitrification, though still enabling the potters to fire the vessel at a low temperature. Coupled with these experiments with body material are experiments with opacifying glazes, resulting in a new-look Islamic pottery that to start with closely resembled Chinese porcelain, until the innovative spirit of the Muslim potters created new forms of decoration with which to transform these vessels even further.