(BaO, Alkaline Earth, Molecular weight 153.4, Expansion: 0.129, Fusion: 1923°C)
Barium is a very active flux at high temperatures, even more so than calcium. It becomes less active at medium and low temperatures. At higher temperatures, it is an active flux even when used in small amounts, improving the gloss and brilliance, acid resistance, and mechanical strength of the glaze.
Barium is probably best known for it’s ability to produce beautiful, richly-colored, velvety-matte glazes, especially in reduction atmospheres. Be aware that such high barium glazes can have surfaces susceptible to leaching, and should not be used on food-contact surfaces.
A small amount of boron in barium glazes can form a pronounced eutectic, giving very fluid melts.
Barium Color Response:
The presence of barium in a glaze intensifies nearly all colors: it produces excellent results with rutile and cobalt, gives stunning turquoise blue with copper, and intensifies blue celadons.
Barium Carbonate (BaCO3, Molecular weight 197)
Barium carbonate is the most common source of barium in glazes. It starts to decompose into barium oxide (BaO) at around 950 C in reduction, but in oxidation it remains in the carbonate form, acting as a refractory opacifier. Barium carbonate is insoluble in water but easily dissolved by stomach acids, making it poisonous by ingestion.
This article taken wholly from
Grimmer, Stephen. “A Short Course on Glaze Chemistry for Ceramic Artists.” Winnipeg: 2009.
Currie, Ian. Revealing Glazes Using the Grid Method. Maryvale, Queensland, Australia: Bootstrap Press, 2000.
Currie, Ian. Stoneware Glazes : A Systematic Approach. Maryvale, Queensland, Australia: Bootstrap Press, 1986.
Hamer, Frank and Hamer, Janet. The Potter's Dictionary of Materials and Techniques. Philadelphia: University of Pennsylvania Press, 19??.
Hansen, Tony. The Magic of Fire Reference. Medicine Hat, Alberta, Canada: Digital Fire Corporation, 1998.
Rhodes, Daniel. Clay and Glazes for the Potter. New York: Chiltons, 1973.