Defect · Glaze firing
Overfired glaze
Also called: melted glaze
Glaze has run, lost its intended surface quality, or absorbed clay body color deeply.
- Appears at
- Glaze firing
- Severity
- Affects function
- How common
- uncommon
Causes
Most likely
- ·Firing exceeded the glaze's rated cone
- ·Hold at peak was too long
Prevention
- ·Use witness cones to confirm final temperature
- ·Record actual firing curves and adjust schedule
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 overfired glaze happen?
- Most often: Firing exceeded the glaze's rated cone. Other causes: Hold at peak was too long..
- Can overfired glaze be fixed?
- Not reliably once it has happened; the fix is upstream, in prevention.
- How do I prevent overfired glaze?
- Use witness cones to confirm final temperature. Record actual firing curves and adjust schedule.
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.