9.2: Bisque Firing- Purpose and Process
- Page ID
- 299317
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The Role of Bisque Firing in the Ceramic Process
- Primary Purpose: Bisque firing transforms greenware into porous yet stable ceramic ware, making it easier to handle and glaze.
- Degassing: It eliminates organic materials and impurities from the clay body, ensuring a cleaner glaze application.
- Strengthening: Bisque-fired pieces are less fragile than greenware, reducing the risk of damage during glazing.
- Foundation for Glazing: The porous surface allows glazes to adhere effectively, making it a critical step in ceramic production.
Preparing Wares for Bisque Firing: Drying, Wadding, and Stacking
- Thorough Drying: Ensure pieces are completely dry to avoid steam explosions during firing. Preheating the kiln can help eliminate residual moisture.
- Wadding: In some cases, wads of clay are placed under pieces to prevent sticking to the kiln shelf.
- Stacking Strategies: Bisque pieces can be stacked tightly since they will not fuse during this firing stage, maximizing kiln efficiency.
- Inspection: Check for cracks, sharp edges, or inconsistencies before loading the kiln to ensure high-quality results.
Optimizing Bisque Firing Schedules for Different Clay Bodies
- Low-Fire Clay: Bisque firing typically reaches Cone 04–06 (1,820–1,940°F) for earthenware.
- Mid-Range and High-Fire Clay: Stoneware and porcelain are usually bisque fired at Cone 08–06 (1,730–1,830°F), depending on their specific requirements.
- Slow Ramps: Gradual temperature increases are vital for thicker or more complex pieces to avoid cracking.
- Hold Periods: A soak at the top temperature ensures complete burnout of organic material.
Assessing Bisque Ware: Identifying Issues Before Glaze Firing
- Cracking or Warping: Check for structural flaws caused by uneven drying or rapid temperature increases.
- Porosity: Ensure the bisque ware is porous enough for effective glaze application.
- Residual Carbon: Look for black spots or odors, indicating incomplete burnout of organic material.
- Surface Quality: Smooth out rough edges or surface imperfections before glazing.
Re-Bisque Firing: When and Why It Might Be Necessary
- Underglazed Pieces: Re-bisque firing can stabilize underglaze decorations before applying a glaze coat.
- Correcting Issues: If the original bisque firing was incomplete, a re-bisque ensures proper burnout of impurities.
- Low-Quality Bisque: Re-bisque firing can strengthen ware that feels overly fragile or brittle.
- Caution: Avoid multiple bisque firings on the same piece, as repeated heat exposure can weaken the clay body.