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 mattes and crystalline surfaces. TiO2 - Titanium dioxide is available pure or in rutile. It is a complex material because of its opacifying, crystallizing, and multitude of color responses. It is used to opacity glazes.
Zirconium has a very low thermal expansion.
BaO - Barium oxide is supplied by barium carbonate. It also has unique color responses. It is a powerful auxiliary alkaline flux. Its expansion is lower than soda or potash. It reacts easily with silica to form low melting lead silicates of high gloss and deep character.