9.1: Overview of Kiln Firing
- Page ID
- 299316
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Understanding the Stages of Firing: Dehydration, Quartz Inversion, and Vitrification
- Dehydration: At around 660°F (350°C), chemically bound water in the clay evaporates, marking the transition from raw clay to ceramic material. This is a crucial step that must proceed slowly to avoid cracking.
- Quartz Inversion: Occurring at 1,063°F (573°C), quartz crystals in the clay expand and rearrange, causing a temporary increase in volume. Careful ramp rates are essential during this stage to prevent thermal shock.
- Vitrification: At high temperatures, fluxes in the clay melt and bond particles together, creating a dense, durable ceramic body. The degree of vitrification depends on the clay body and firing temperature.
- Understanding Transformation: Each stage is interdependent, and managing these transitions ensures the integrity of the final piece.
Types of Kilns: Electric, Gas, Wood, and Alternative Fuels
- Electric Kilns: Clean, user-friendly, and ideal for consistent oxidation firings, electric kilns are commonly used for functional and decorative ware. They are highly controllable and efficient for small studios.
- Gas Kilns: Offering the ability to create reduction atmospheres, gas kilns allow for more dynamic surface effects, making them popular for high-fire stoneware and porcelain.
- Wood Kilns: Valued for their organic, unpredictable results, wood kilns require intense labor and skill. Ash deposits during firing create unique textures and surfaces.
- Alternative Fuels: Experimental artists may use oil, propane, or even sawdust in pit or raku firings for creative and unpredictable results. Each fuel source impacts the final surface finish uniquely.
The Significance of Firing Schedules and Heatwork
- Ramp Rates: Slow, steady increases in temperature ensure even heating and minimize stress on pieces. Abrupt temperature changes can cause cracking or warping.
- Soak Periods: Holding the kiln at a specific temperature allows glazes to mature and ensures thorough vitrification of the clay body.
- Cooling Cycles: Controlled cooling can enhance certain glaze effects, such as crystalline formations or subtle color shifts. Rapid cooling risks thermal shock.
- Heatwork: Beyond peak temperature, total heat energy (time and temperature combined) affects clay and glaze maturation. Witness cones are critical for monitoring this.
Kiln Atmospheres: Oxidation, Reduction, and Neutral
- Oxidation Atmosphere: Common in electric kilns, oxidation maintains an oxygen-rich environment, resulting in bright, consistent glaze colors.
- Reduction Atmosphere: Achieved in gas or wood kilns, reduction limits oxygen, encouraging unique surface effects like celadons or copper reds.
- Neutral Atmosphere: Found in some gas or soda kilns, neutral firings balance oxygen and reduction to produce subtle variations in surface quality.
- Atmosphere Selection: The choice of atmosphere depends on the desired finish and the chemical reactions required for specific glazes.
Safety Practices and Environmental Considerations in Firing
- Ventilation: Proper kiln ventilation prevents exposure to harmful fumes, such as those from burning glazes or fuel. Install an exhaust system or fire outdoors for safety.
- Protective Gear: Wear heat-resistant gloves and avoid direct contact with kiln surfaces during operation. Eye protection is essential when peeking into the kiln.
- Energy Efficiency: Optimize kiln loads and firing schedules to reduce energy consumption.
- Environmental Impacts: Consider the sustainability of fuel sources and responsible disposal of kiln waste.