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Feldspar

An indispensable material in the ceramic industry. Most ceramic bodies employ feldspar as a flux to vitrify them at a lower temperature (the feldspar creates a glaze that glues the more refractory particles together to form the fired matrix). Most medium and high temperature glazes employ it as a flux. Feldspars are naturally occurring crystalline rocks that will melt and cool to form a glass (nature cooled them slowly (devitrified) to for crystalline minerals. There are many kinds of feldspars, but in ceramics soda, potash and lime feldspars are the most common.

Porcelains can contain up to 50% feldspar, stoneware bodies around 15%. Feldspar sources K2O and Na2O to glazes, these can produce very brilliant results. However, the high KNaO produces a high thermal expansion which in turn produces crazing. Thus it is important to control the amount of feldspar and employ materials that source other low expansion oxides like CaO, MgO, Li2O, BaO, SrO, etc.

Links

Glossary Feldspar Glazes
Feldspar is a natural mineral that, by itself, is the most similar to a high temperature stoneware glaze. Thus it is common to see alot of it in glaze recipes. Actually, too much.
Minerals K-Feldspar
Minerals Na-Feldspar
Oxides K2O - Potassium Oxide
Oxides Na2O - Sodium Oxide, Soda

By Tony Hansen


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