Defect · Glaze firing
Bloating
Also called: swelling
Raised blisters or bubbles in the clay body, visible on fired work, often with glaze bulging over them.
- Appears at
- Glaze firing
- Severity
- Structural
- How common
- uncommon
Causes
Most likely
- ·Overfiring past clay body maturation point
- ·Reduction atmosphere in an oxidation-rated body, trapping gases
- ·Iron or sulfur impurities off-gassing late in the firing
Prevention
- ·Fire within the clay body's rated cone range
- ·Use a longer bisque to burn out organics before glaze firing
- ·Ensure adequate kiln ventilation during bisque
Can it be fixed?
Not reliably — this one is prevented, not repaired. A cracked or bloated pot is a test tile now.
Materials involved
Glaze materials whose chemistry sits behind this defect — each links to its reference page.
Related defects
Questions
- Why does bloating happen?
- Most often: Overfiring past clay body maturation point. Other causes: Reduction atmosphere in an oxidation-rated body, trapping gases. Iron or sulfur impurities off-gassing late in the firing..
- Can bloating be fixed?
- Not reliably once it has happened; the fix is upstream, in prevention.
- How do I prevent bloating?
- Fire within the clay body's rated cone range. Use a longer bisque to burn out organics before glaze firing. Ensure adequate kiln ventilation during bisque.
Sources. Compiled from Claybench's defect reference — the descriptions, causes and remedies that appear consistently across standard ceramics references and studio practice; no single source. It is the same reference the photo diagnosis tool reasons over. Where the Wikibooks Ceramicware Defects Handbook covers a defect it is linked above.
Not sure which defect you're looking at?
Claybench can read a photo of the pot against this same reference and rank the likely causes for your clay, glaze and firing.