Feldspars are minerals of varying composition commonly used by potters. Feldspars form a glassy, white surface when fired high enough. They have a very long range, they begin melting at cone 4 and continue fusing beyond cone 10. They also tend to stiffen a glaze due to their high alumina content. In ceramics there are two basic categories of feldspars: potash feldspars, in which the primary melting oxide is potassium, and soda feldspars in which the primary melter oxide is sodium. Soda and potash have the highest thermal expansion and contraction rate of all the ceramic melter oxides, they promote color brilliance and luster at most firing temperatures, and they encourage specific color results.
Ceramic Raw Materials
Do you need to learn what ceramic raw materials are and how they function in clay and glaze recipes? Well, you’ve come to the right place. We’ve gathered some great articles on ceramic raw materials and plopped them right into this section. Learning how these materials work together enables you to better achieve the results you want in your work. Plus, if you haven't already, be sure to download your free copy of the Ceramic Raw Materials: Understanding Ceramic Glaze Ingredients and Clay Making Materials, a directory of ceramics suppliers carrying all the raw materials you will need, plus reference material for the studio artist - professional or amateur, student or teacher.
Feldspars are important ingredients in clay bodies and glazes. In both applications, their primary function is to supply ﬂuxes to the formulations, but they also provide additional alumina (Al2O3) and silica (SiO2). Feldspars are naturally occurring minerals and are generally classiﬁed as either potash (potassium) or soda (sodium) feldspars based upon the predominant alkali metal element (the ﬂux) that is present. The minerals commonly referred to as lithium feldspars are not true feldspars, but they are aluminosilicates like feldspars and contain the ﬂuxing element lithium, and are used for the same purposes as the feldspars.
When we ran a couple of features recently on using paper clay (see “Paper, Clay, Steel: Combining Disparate Materials to Create Strong, Lightweight Ceramic Sculptures” and “Lose Weight, Get Strong: Put Your Ceramic Work on the Paper Clay Diet”), I received some emails from readers asking for more, more, more! Many were interested in more… Read More »
The objective is to locate one single earth material that alone almost provides the desired surface, and then to add as few additional materials as possible. I call this primary material, which almost achieves the desired glaze surface, a “glaze core.”