Debunking the Myth: Clay and Crystalline Glazes

A common misconception among potters is that clay is incompatible with crystalline glazes. Many believe that the presence of clay will hinder the formation of crystals, leading to dull, lifeless glazes. However, as evidenced by the numerous examples created by potters around the world, this is simply not the case.

The Science Behind It

Crystalline glazes are formed when zinc oxide is the alkaline earth flux in a glaze, with a specific chemistry. The resulting glaze develops a shimmering, crystalline surface. While it’s true that clay is a common ingredient in many glazes, it is incorrectly believed to be an ingredient that will “kill” the growth of the crystals, which is not true.

Key Factors Influencing Crystallization

Several factors can influence whether a glaze with clay will crystallize:

• Clay content: The amount of clay used in the glaze can impact crystallization. But how it is used in the overall chemistry is the real complication..
• Firing temperature: The temperature at which the glaze is fired is crucial. Too low, and the glaze will over crystallize; too high, and the glaze will not be able to form any crystals.
• Cooling: Controlling the cooling of the kiln  affects crystal size and formation. Precise cooling temperature holds promote larger, more defined crystals.
• Application: Crystalline glazes need to have a very precise application for the best  results

Examples of Crystalline Glazes with Clay

Below are some glazes that demonstrate that clay can be successfully incorporated into crystalline glaze formulas without compromising the desired crystalline effect.

• A glaze with 22.16% clay: This glaze, despite its high clay content, exhibited excellent crystallization. See photo below.
• A glaze with 9.53% clay: This glaze, containing a significant amount of clay, still crystallized just fine. See photo below.
• A glaze with 24.35% clay: This glaze, using both traditional kaolin and calcined kaolin, successfully formed crystals. See photo below.

While the misconception that clay is incompatible with crystalline glazes persists, numerous examples prove otherwise. The key to creating successful crystalline glazes with clay lies in understanding the factors that influence crystallization and carefully formulating your glaze. By experimenting and refining your techniques, you can create stunning crystalline glazes that incorporate clay.

The Ceramic Materials Workshop’s Crystal Ball course is designed to demystify the world of glazes, providing you with a solid foundation in glaze chemistry, formulation, and application.

Ceramic Materials Workshop can help you learn!  Studying glaze and clay chemistry with us can be a transformative experience for any ceramic artist. The expert-led instruction by Matt Katz, comprehensive curriculum, hands-on learning, personalized feedback, exclusive resources, real-world applications, vibrant community, and flexible online courses make CMW an exceptional choice for advancing your ceramic practice. Embrace the science behind the art, and unlock new dimensions in your creative work with the Ceramic Materials Workshop.

Want to learn more?

Make sure to check out our other blog article – 10 Reasons Why You Should Take a Glaze Chemistry Course!    

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-The CMW Team