8.4: Formulating Glazes for Specific Effects
- Page ID
- 299311
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Strategies for Creating Matte, Glossy, and Textured Glazes
- Matte Glazes: Increase the alumina content or use materials like magnesium carbonate to create a soft, matte surface. Matte finishes are also achieved by underfiring or slowing the cooling cycle in the kiln.
- Glossy Glazes: Add more fluxes, such as feldspar or calcium carbonate, to lower the melting point and increase the glaze's fluidity, resulting in a shiny surface. Transparent glazes often achieve high gloss when applied thinly.
- Textured Glazes: Introduce materials like grog, ash, or silica sand to create rough, textured surfaces. Controlled melting of these additives during firing can create unique, tactile finishes.
- Testing: Test combinations of these adjustments to understand their effects and fine-tune recipes for specific surfaces.
Developing Glazes for Low-Fire, Mid-Range, and High-Fire Applications
- Low-Fire Glazes: Designed for temperatures between Cone 06–04 (1,820–1,940°F), these glazes often feature bright, vivid colors due to the stability of colorants at lower temperatures.
- Mid-Range Glazes: Fired at Cone 5–6 (2,102–2,192°F), these glazes balance durability and color vibrancy. They are popular for functional ware due to their increased strength.
- High-Fire Glazes: At Cone 9–10 (2,328–2,380°F), high-fire glazes yield earthy tones and subtle finishes, as many colorants volatilize or alter at extreme temperatures.
- Recipe Adjustments: Adjust fluxes and silica levels in glaze recipes to ensure melting occurs at the appropriate temperature for your firing range.
Special Effects in Glazing: Crystals, Celadons, Raku
- Crystalline Glazes: These glazes rely on high levels of zinc oxide and slow cooling cycles to grow crystals within the glaze. Experiment with extended holds at specific temperatures to encourage crystal formation.
- Celadon Glazes: Thin, transparent glazes with a soft green tint, celadons are typically applied over light-colored clay bodies. Iron oxide is the key colorant for achieving this effect.
- Raku Glazes: Formulated to withstand rapid cooling, raku glazes often include crackling or metallic finishes. The process involves removing pieces from the kiln while hot and cooling them in combustible materials.
- Experimentation: Test these techniques to understand the balance between glaze composition and firing schedules for achieving these effects.
Adjusting Glaze Viscosity and Surface Tension for Different Applications
- Viscosity: Adjust glaze thickness by adding water or flocculants like Epsom salts to achieve the desired consistency for brushing, dipping, or spraying.
- Surface Tension: To prevent crawling or uneven application, adjust the balance of fluxes and stabilizers. A small amount of bentonite can improve glaze adhesion.
- Testing Application Methods: Different application methods may require varying viscosities. For example, spraying requires thinner glazes, while dipping benefits from medium viscosity.
- Troubleshooting: Observe how the glaze behaves during application and firing, and make incremental adjustments to refine its performance.
Eco-Friendly and Food-Safe Glaze Considerations
- Non-Toxic Materials: Use non-toxic fluxes, colorants, and opacifiers to ensure your glazes are safe for functional ware. Avoid lead, cadmium, or other hazardous materials.
- Food Safety Testing: Test glazes for leaching by sending samples to a certified lab. Glazes for food-safe ware should be stable and non-reactive.
- Environmentally Friendly Practices: Reuse excess glaze and responsibly dispose of glaze waste. Avoid washing glazes with toxic materials into drains.
- Documentation: Clearly label glazes as food-safe or non-food-safe, and educate yourself about the regulations in your region for functional pottery.