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A 'frit' (sometimes spelled fritt) is a ground glass or glaze used in pottery. Some materials have to be fritted before they can be used because they are soluble or toxic. For example, lead (used in glazes as a flux) is toxic, and borax, used in glaze as a flux and a glass former, is soluble. The modern potter uses lead as a frit of lead bisilicate (PbO.2SiO₂), lead sesquisilicate (2PbO.3SiO₂) or lead monosilicate (PbO.SiO₂). Borax will be used as a frit of sodium diborate (Na₂.2B₂O₃.10H₂O) or anhydrous borax (Na₂.2B₂O₃).^[1]
Near eastern pottery from the 13th century made use of frits in the clay body to achieve white wares that looked like Chinese porcelain, whose raw materials were inaccessible and little understood. Iznik pottery from the late 15th century was made of 80% silica, 10% glass frit and 10% white clay, with added lead and soda to reduce the firing temperature.^[2] In Europe from the 16th to the 18th century, several attempts were made to imitate porcelain using frit; these are called soft-paste porcelain. The development of true porcelain by the Meissen pottery lead to the abandonment of frit bodies. However, some imitations of Iznik ware made at Kütahya today still use a frit body.
The porcelain enamel industry also uses fritted glass as a coating. This glass is of varying compositions, and usually includes a nickel or cobalt containing base coat, followed by a titania-bearing cover coat. Porcelain enamel frits are melted, then quick-cooled (quenched), and processed further by grinding, to allow application by a number of different means. This frit is the basis of coatings on appliances and sanitary ware.

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References

References

1. Fournier, Robert, ''Illustrated Dictionary of Practical Pottery'' (Van Nostrand Reinhold, 1973 ISBN 0-442-29950-8
2. Atasoy, N., and Raby, J. ''Iznik'', (London, Alexandria Press, 1989)