Alumina

Alumina (Al₂O₃) in ceramic glazes stiffens the melt. At mid and high fire temperatures, low alumina glass (like that in glass bottles) becomes completely liquid and will run off the pot.

In the Unity Molecular Formula, Alumina is measured in terms of molecules of flux. For example, an alumina level of 0.5 means that there are 0.5 molecules of alumina for each molecule of flux - in other words, there is twice as much flux as alumina.

Here is a general prediction of how glazes move based on the alumina content. Specifics might be different based on fluxes used and other aspects of glaze chemistry.

1. < 0.20: Very high glaze movement, extremely runny
2. 0.20 - 0.25: High glaze movement, but the fluidity of the glaze melt allows for unique crystallization effects
3. 0.3 - 0.5: Glaze melts enough to heal minor application issues, but still stiff enough to stick to the ware. Surface tension is high enough so glaze "gloops" on sharp angles. Most standard glazes live here.

4. 0.5: Glaze is rather stiff and shows little movement. Underglaze designs don't smudge and retains their edges

Alumina Powder (Calcined Alumina)

You can buy powdered alumina. It may also be called calcined alumina (because it is made by calcining alumina hydrate). Do not use alumina powder in glazes unless you know what you're doing. Alumina powder does not dissolve nearly as well as other sources of alumina. Undissolved particles do not release alumina into the glaze melt and will matte the glaze surface.

Created 2024-07-07.

Home > Q Science > QD Chemistry > Alumina