8.7: Troubleshooting
- Page ID
- 299314
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Introduction to Glaze Chemistry
1. Glaze Not Melting Properly:
- Cause: Insufficient flux content or incorrect firing temperature.
- Solution: Adjust the ratio of flux to silica and alumina in the glaze recipe. Confirm the kiln is reaching the intended temperature.
- Tip: Test adjustments in small batches and document changes for future reference.
- Prevention: Use a pyrometer or witness cones to verify accurate kiln performance.
2. Crazing or Shivering:
- Cause: Thermal expansion mismatch between the glaze and clay body.
- Solution: Modify the glaze recipe to better match the clay body’s coefficient of expansion. For crazing, reduce silica. For shivering, increase it.
- Tip: Test glazes on multiple clay bodies to identify compatibility issues.
- Prevention: Use test tiles to evaluate fit before applying glazes to finished pieces.
Triaxial Glaze Testing
1. Difficult to Interpret Results:
- Cause: Inconsistent labeling or recording during the testing process.
- Solution: Clearly label all test tiles and keep detailed notes for each variable being tested. Photograph results for visual reference.
- Tip: Use a triaxial chart to map your test samples and correlate findings with specific recipes.
- Prevention: Develop a standardized system for testing and documentation.
2. Tests Not Reproducible:
- Cause: Variability in ingredient measurement or firing conditions.
- Solution: Weigh ingredients precisely and use calibrated equipment for firing. Ensure consistent application thicknesses.
- Tip: Fire all test tiles in the same load to eliminate temperature inconsistencies.
- Prevention: Double-check measurements and firing schedules before starting tests.
Formulating Glazes for Specific Effects
1. Unintended Colors:
- Cause: Unexpected interactions between colorants or changes in firing atmosphere.
- Solution: Test colorants in isolation before combining them. For reduction effects, ensure sufficient oxygen reduction during firing.
- Tip: Experiment with small test batches to explore new combinations.
- Prevention: Study how specific oxides behave under different conditions to anticipate outcomes.
2. Crystals Not Forming:
- Cause: Cooling cycle too rapid or glaze composition lacks sufficient zinc oxide.
- Solution: Slow down the cooling process and increase zinc oxide content in the glaze recipe.
- Tip: Hold the kiln at the ideal temperature for crystal growth (e.g., 1,850°F) to encourage formation.
- Prevention: Use a programmable kiln for precise temperature control.
Making and Using Glaze Test Tiles
1. Glaze Looks Different on Test Tiles vs. Pieces:
- Cause: Test tiles may differ in texture, shape, or clay body from the final work.
- Solution: Use test tiles made from the same clay and fired under identical conditions as your pieces.
- Tip: Design test tiles that mimic the surfaces of your final pieces, such as flat and curved areas.
- Prevention: Test glazes on both tiles and sample pieces to ensure consistency.
2. Running Glazes:
- Cause: Excessive flux content or over-application.
- Solution: Reduce the flux in the glaze recipe or apply thinner coats. Incline test tiles slightly to mimic how glaze flows on vertical surfaces.
- Tip: Test glazes on inclined tiles to gauge their movement during firing.
- Prevention: Observe glaze behavior on test tiles before using it on finished pieces.