Fritware

İznik pottery, an example of fritware

Fritware, also known as Islamic stone-paste, is a type of pottery in which frit is added to clay to reduce its fusion temperature. As a result, the mixture can be fired at a lower temperature than clay alone.

Fritware refers to a type of pottery which was first developed in the Near East, where production is dated to the late first millennium AD through the second millennium AD. Frit was a significant ingredient. A recipe for “fritware” dating to c. 1300 AD written by Abu’l Qasim reports that the ratio of quartz to “frit-glass” to white clay is 10:1:1.[42] This type of pottery has also been referred to as “stonepaste” and “faience” among other names.[43] A ninth century corpus of “proto-stonepaste” from Baghdad has “relict glass fragments” in its fabric.[44] The glass is alkali-lime-lead-silica and, when the paste was fired or cooled, wollastonite and diopside crystals formed within the glass fragments.[45] The lack of “inclusions of crushed pottery” suggests these fragments did not come from a glaze.[46] The reason for their addition would have been to release alkali into the matrix on firing, which would “accelerate vitrification at a relatively low firing temperature, and thus increase the hardness and density of the [ceramic] body.”[46] Whether these “relict glass fragments” are actually “frit” in the more ancient sense remains to be seen.

Iznik pottery was produced in Ottoman Turkey as early as the 15th century AD.[47] It consists of a body, slip, and glaze, where the body and glaze are “quartz-frit.”[48] The “frits” in both cases “are unusual in that they contain lead oxide as well as soda”; the lead oxide would help reduce the thermal expansion coefficient of the ceramic.[49] Microscopic analysis reveals that the material that has been labeled “frit” is “interstitial glass” which serves to connect the quartz particles.[50] Tite argues that this glass was added as frit and that the interstitial glass formed on firing.[51]

Frit was also a significant component in some early European porcelains. Famous manufacturers of the 18th century included Sèvres in France, and at Chelsea, Derby, Bow, Worcester and Longton Hall in England.[1][52] At least one frit porcelain remains in production at Belleek, County Fermanagh, Northern Ireland. This factory, established in 1857, produces ware that is characterised by its thinness, slightly iridescent surface and that the body is formulated with a significant proportion of frit.[1]

References

• History of World Ceramics