Ceramic Technical Hints: On Body Fluxing Minerals

In this Ceramic Technology Hints article we discuss those minerals that allow a ceramic body to vitrify during firing. Vitrification implies "glassification," and indeed, a glassy phase is always present in the fired body. Scientist are sometimes dismayed that glassification is not a word to be found in a dictionary, but the word is more self-defining than vitrification so I have decided to make it a perfectly good word by adding it to my spell checker, so there.

Some ceramic bodies contain a single component. Art clays often contain enough fluxing mineral content to vitrify during firing. Pure clays have very high firing temperatures but some lovely art clays, although not pure in heart, fire at lower temperatures.

Here are some common materials used in ceramic bodies to promote glassification or vitrification:

China Stone:

The British are always the ones to get the good stuff ceramic-material-wise. China Stone is a mixture of clay and fluxing minerals. I know of no ceramic body that is a single-component containing only china stone, but that does not mean that such bodies don't exist. Triaxial bodies, which means 3-component bodies, consist of clay, feldspar, and quartz. The classical composition is porcelain which has 50% clay, 25% feldspar, and @5% quartz. China stone is substituted for some of the clay and feldspar.

China stone is partially decomposed feldspar. You know that clay is formed when feldspar is decomposed by hydrothermal activity. Well, china stone is still working on that process. It contains enough feldspar that it can be used to form a glaze for ceramic bodies although that is not a popular thing to do now days, but it is used in some British glazes.

China stone is also called Cornish Stone or Cornwall Stone so now you know where it comes from. You've see the Pirates of Penzance by Gilbert and Sullivan, have you not? I'm am the very model of a modern major general. I am an orphan boy! Read about British clays and other earthy minerals at the following shortened url: http://tinyurl.com/3yxq2h

Feldspar:

Feldspar is a common component of granite and other igneous rocks.