A frit (sometimes spelle 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, some lead compounds are 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).