7.5: Troubleshooting

Engobes and Slip Decoration

1. Slip Peeling Off:

- Cause: Slip doesn’t adhere properly to the clay surface due to inconsistent moisture levels or insufficient scoring.

- Solution: Apply slip to leather-hard clay, as it provides the ideal balance of moisture for bonding. Score and slip the area if attaching layers.

- Tip: Avoid over-wetting the clay surface before applying the slip, as excess moisture can weaken the bond.

- Prevention: Test your slip on sample pieces to ensure compatibility with your clay body and firing temperature.

2. Cracking:

- Cause: The moisture content of the slip is too different from the clay body, causing uneven shrinkage.

- Solution: Adjust the moisture levels of your slip to match the clay body. Let the slip settle slightly before application to reduce excess water.

- Tip: Avoid applying thick layers of slip, as they are more prone to cracking during drying or firing.

- Prevention: Allow the piece to dry slowly and evenly to minimize stress on the surface.

3. Color Burnout:

- Cause: The firing temperature exceeds the stability range of the colorants in the slip.

- Solution: Test slips at different firing ranges to identify the optimal temperature for color retention.

- Tip: Use oxides or stains with proven stability at your desired firing range.

- Prevention: Keep detailed firing records to track which formulas perform best under specific conditions.

Carving and Incising

1. Tool Dragging:

- Cause: Dull tools or excessive pressure can lead to uneven lines and jagged edges.

- Solution: Keep tools sharp and well-maintained. Use light, consistent pressure while carving.

- Tip: Practice carving on scraps of leather-hard clay to refine your technique.

- Prevention: Regularly clean and sharpen tools to ensure smooth operation.

2. Detail Loss During Firing:

- Cause: The edges of carvings soften during firing due to the vitrification process.

- Solution: Carve slightly deeper than intended to account for this softening effect.

- Tip: Use firmer clay bodies with less shrinkage for pieces requiring detailed carvings.

- Prevention: Test firing with small samples to gauge how much detail is retained.

3. Surface Cracking Around Carvings:

- Cause: Carving too deeply weakens the structure, especially in thinner areas of the piece.

- Solution: Avoid carving too close to edges or into walls that are too thin. Reinforce areas around deep carvings with additional clay if necessary.

- Tip: Compress the surface with a rib tool before and after carving to reduce stress on the clay body.

- Prevention: Allow the piece to dry slowly and evenly to minimize cracking.

Glaze Application Techniques

1. Glaze Too Thick or Thin:

- Cause: Incorrect application or inconsistent glaze consistency.

- Solution: For dipping, adjust your dipping time to achieve an even thickness. For brushing, use multiple thin coats rather than a single thick coat.

- Tip: Mix glazes thoroughly before application to avoid settling of materials.

- Prevention: Use test tiles to determine the ideal application thickness for each glaze.

2. Glaze Crawling:

- Cause: Contamination on the bisque surface or uneven application of glaze.

- Solution: Clean the bisqueware with a damp sponge to remove dust or oils. Apply glaze evenly and avoid pooling in certain areas.

- Tip: Add a small amount of bentonite to the glaze to improve adhesion.

- Prevention: Avoid handling bisqueware with greasy hands or applying overly thick glazes.

3. Pinholing in Glaze:

- Cause: Trapped air or gases escape during firing, leaving small holes in the glaze surface.

- Solution: Slow down the firing schedule, especially during the early stages, to allow gases to escape gradually.

- Tip: Ensure proper bisque firing to remove residual moisture and organic material from the clay body.

- Prevention: Maintain a steady cooling rate in the kiln to prevent sudden temperature changes.