Have you ever looked at a ceramic piece and wondered how a single glaze could produce such stunning variations in color and texture? Streaks of blues swirling into browns, opaque sections blending with transparent areas – it’s a visual spectacle that often leaves even experienced ceramicists scratching their heads.
In this blog post, we’ll delve into the fascinating world of “phase separation” in glazes, breaking down the science behind this captivating effect, as explained by Matt from Ceramic Materials Workshop.
Wait, wait, wait – I am dealing with an odd sort of…flashing? Reading CMW’s blog article: Sodium Flashing: Unmasking the Ghostly Glaze Mystery
“Glazes are glass, and glass can be transparent, which means light can pass through it,”Â
Conversely, opaque glazes block light, resulting in a pastel-like appearance due to the “white” reading of opacity in glaze chemistry. He illustrates this with a simple comparison: a clear glaze with cobalt versus an opaque glaze with cobalt, showcasing the subtle color differences.
“What if I told you it’s just one glaze? Like literally just one? It’s not layered, it’s not anything. And it’s actually a pretty consistent common chemical reaction that we have complete control over,”Â
The Science Behind the Swirls
Phase separation occurs due to the transition between transparent and opaque glass within the glaze. This transition doesn’t happen uniformly; instead, it occurs in “pockets.” Matt explains, “Although we only have one glass, there’s literally only one recipe for this glass that when it melts, it actually splits into two different chemistries of glass.” One part becomes transparent, and the other opaque. These two glasses then “intermingle and mix,” creating the characteristic streaks and swirls.
This process is likened to “pouring milk into water,” where initial streaks eventually blend into a uniform opacity. “Glass is pretty much doing the same thing, making that phase separation reaction,” he notes.
Key Characteristics and Influencing Factors
Several key factors influence phase separation:
- Blue Hue: Phase separation inherently produces a bluish tint. “It is always going to be a blue shade. It’s not like intensely blue, but there’s definitely a bluish hue to that phase separation in all forms,” Matt emphasizes.
- Thickness: The effect is more pronounced in thicker glaze applications. “Phase separation definitely occurs more on areas where the glaze builds up—lips, edges, embossed areas, throwing rings, those types of places,” he explains.
- Chemical Composition: The glaze’s chemistry plays a crucial role. Matt references Stull’s Map, a tool used to understand the relationship between glaze components and their effects. He explains that phase separation occurs in a specific “micro-region” on this map, where “you get this much of this and this much of that, you’re going to get this.”
- Titanium’s Role: While not essential, titanium can enhance phase separation. “It really enables phase separation to be less sensitive to things like thickness and application,” Matt clarifies. He compares titanium to “adding salt to caramel,” improving the overall result without being a necessity.
Debunking Myths and Misconceptions
Matt also addresses common misconceptions:
- Texture is not the cause: “It has nothing to do with texture whatsoever,” he states, emphasizing that thickness, not texture, is the key factor.
- Durability Concerns: He reassures viewers that phase-separated glazes are durable, citing lab tests that found “no correlation between phase separation or lack of durability.”
- Titanium is not required: Many believe titanium is essential for phase separation, but Matt proves otherwise, showing examples of glazes with no added titanium.
I am curious about other myths CMW has busted- such as Lead, and kiln maintenance! Find out more here!
Popular Phase-Separated Glazes
He goes on to discuss popular glaze types that utilize phase separation:
- Floating Blue: This glaze is known for its distinct brown-to-blue transition. “That phase separation is blue, and so you happen to get this sort of surreal transition between brown and blue,” Matt explains.
- Chun (Jun) Glazes: Ancient Chinese glazes, often celadons or copper reds, that utilize phase separation. Copper reds in particular, when phase separated, often result in a purple color. “If you know your color theory, what happens when you mix red and blue? You get purple,” he explains.
- Nuka Glazes: A Japanese tradition using ash-based glazes. Matt clarifies that “plant ash is just silica and alumina and calcium and sodium generally,” dispelling the myth of special ingredients.
Want to learn about other glazes- such as Shino Glazes, crystalline or Bristol? Read about them in CMW’s blog now!
Conclusion
Phase separation is a fascinating chemical reaction that creates stunning visual effects in ceramic glazes. By understanding the underlying science, ceramicists can harness this phenomenon to create unique and captivating pieces. Matt’s detailed explanation demystifies this complex process, empowering viewers to explore the possibilities of phase separation in their own work.
Ready to dive deeper?
Loved learning about ceramic glazes? Want to go even deeper? Check out our Workshops & Courses, now available in Spanish, or YouTube Channel where Matt breaks it all down, myth-busting and Stull chart included!
