8.7: Troubleshooting
- Page ID
- 299314
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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.