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Understanding Ceramic Oxides

Section: Glazes, Subsection: Chemistry

Description

Fired glazes are composed of oxide building blocks. Each of the oxides contributes different properties to the fired glaze and interacts with others in different ways. Understanding these gives you control.

Article Text

The ancient Chinese thought of glazes as being made of bones, flesh, and blood. They were very perceptive! The silica content of a glaze acts like a framework, the alumina acts to give it body, and the fluxes melt it and impart character acting as the lifeblood.

In understanding fired properties, it is helpful to view materials as sources of oxides. However, remember that although it is chemically possible to supply a given oxide from many materials, often other factors make one of them preferable. For example, kaolin is an ideal source of alumina since it also imparts suspension and hardening properties to the glaze slurry.

Following is a list of the major oxides. There are a multitude of textbooks with more information on this subject. However, the data is widely scattered and thus difficult to study. The best source of information is the oxides area on this website.Not only is each oxide described in detail but properties are assigned so that it can be searched by category. For example, if you need to produce purple you can look up the 'purple' property area and see a list of all the chemistries that produce it.

Major Oxides

Ceramic Oxide Periodic Table

All common traditional ceramic base glazes are made from only a dozen elements (plus oxygen). Materials decompose when glazes melt, sourcing these elements in oxide form. The kiln builds the glaze from these, it does not care what material sources what oxide (assuming, of course, that all materials do melt or dissolve completely into the melt to release those oxides). Each of these oxides contributes specific properties to the glass. So, you can look at a formula and make a good prediction of the properties of the fired glaze. And know what specific oxide to increase or decrease to move a property in a given direction (e.g. melting behavior, hardness, durability, thermal expansion, color, gloss, crystallization). And know about how they interact (affecting each other). This is powerful. And it is simpler than looking at glazes as recipes of hundreds of different materials (each sources multiple oxides so adjusting it affects multiple properties).

In Bound Links


By Tony Hansen




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