Technical Ceramics - Oxides

Common Ceramic Oxides

• SiO2 - Silicon dioxide - silica, feldspar, and kaolin. It is the main glass forming oxide and normally comprises more than 60% of most glazes and clays. It has a low expansion and high melting temperature.

• Al2O3 - Aluminum oxide - kaolin and feldspar. It combines well with silica and basic oxides to give body, durability, and stability to glazes. It has a  low expansion and high melting temperature.

• B2O3 - Boric oxide - borax frits, gerstley borate, (or colemanite). It is a low temperature low expansion equivalent of silica.

• CaO - Calcium oxide - whiting, wollastonite, feldspar, colemanite, or dolomite. It is the principle flux used in medium and high fire glazes. In larger quantities it can give matt qualities through the sbsequant formation of calcium silicate crystals.

• K2O - Potassium oxide -  potash feldspar and cornwall stone. It is an important auxiliary flux used in high temperature glazes. It has high expansion factor.

• Na2O - Sodium oxide feldspar, nepheline syenite and sodium frits. A more powerful flux than potassium for high temperature glazes. It also has a high expansion.

• MgO - Magnesium oxide - talc or dolomite. At lower temperatures, it is a matting agent and opacifier; at higher temperatures, it is an active alkaline flux.

• Fe2O3 , FeO, Fe3O4 - Ferrous-ferric oxide - iron oxide and stained clays. It is the most popularly used colorant. In a reducing atmosphere, it can act as a flux in both bodies and glazes at high temperatures.

• ZnO - Zinc oxide is available in a pure state. It is a low expansion secondary flux, in moderate to higher amounts it acts to produce matt and crystalline surfaces.

• TiO2 - Titanium dioxide is available pure or in rutile. It is a complex material to use because of its capacity to opacify, crystallize, and for the multitude of colour responses that it can produce.

• ZrO2 - Zirconium oxide is available in a pure state and as zircon opacifiers. It is used to opacity glazes. Zirconium has very low thermal expansion.

• BaO - Barium oxide - barium carbonate. Is a flux which encourages the growth of micro-crystals to produce attractive satin-matte surfaces. It also has some unique colour responses.

• Li2O - Lithium oxide - lithium carbonate or lithium feldspar. Is a powerful auxiliary alkaline flux. Its expansion though is lower than soda or potash.

• PbO - Lead oxide - lead frits. Reacts easily with silica to form low melting lead silicates of high gloss and deep character.

• SrO - Strontium oxide - strontium carbonate. Has matting and crystallizing properties similar to barium although it produces much brighter and more fusible glazes with fewer surface defects.