Defect · Drying
S-crack
Also called: base crack, bottom crack
S-shaped crack in the base of a thrown form, visible from the underside or inside after trimming.
- Appears at
- Drying
- Severity
- Structural
- How common
- Common
Causes
Most likely
- ·Insufficient base compression during throwing
- ·Base is too thick relative to walls, causing uneven drying shrinkage
Also possible
- ·Clay body with high silica sand content
- ·Rapid drying on warm surfaces
Prevention
- ·Compress the base thoroughly with a rib or sponge after opening
- ·Match base thickness to wall thickness within ~1.5x
- ·Dry on a ware board, flipped once piece is firm
Can it be fixed?
Not reliably — this one is prevented, not repaired. A cracked or bloated pot is a test tile now.
Related defects
Questions
- Why does S-crack happen?
- Most often: Insufficient base compression during throwing. Other causes: Clay body with high silica sand content. Rapid drying on warm surfaces..
- Can S-crack be fixed?
- Not reliably once it has happened; the fix is upstream, in prevention.
- How do I prevent S-crack?
- Compress the base thoroughly with a rib or sponge after opening. Match base thickness to wall thickness within ~1.5x. Dry on a ware board, flipped once piece is firm.
Further reading. The industrial treatment of this defect in the Ceramicware Defects Handbook on Wikibooks (CC BY-SA 3.0).
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.