In ceramics, the addition of a flux lowers the melting point of the body or glaze. In particular they affect the melting point of silica (SiO2), which melts to form a glassy phase during firing/sintering which bonds the ceramic body or forms the basis of a glaze. The addition of a flux also promotes fusion or vitrification (formation of a glassy phase) at lower temperatures than would otherwise possible without the use of a flux.
Some common fluxes include:
• Nephelene syenite
• Barium carbonate (BaCO3)
• Alkali metal oxides and alkali metal containing feldspars such as potash feldspar (K2O.Al2O3.6SiO2), soda feldspar (Na2O.Al2O3. 6SiO2) and lithium feldspar (Li2O. Al2O3.8SiO2)
• Lead compounds