Why does crawling happen?

Most often: Greasy or dusty bisqueware surface when glaze was applied. Other causes: Glaze applied too thickly, particularly on a high-shrinkage recipe. Glaze has excessive plastic clay, causing shrinkage on drying..

Can crawling be fixed?

Sometimes. Fill crawled areas with the same glaze and refire.

How do I prevent crawling?

Clean bisqueware with a damp sponge before glazing. Apply glaze at recommended thickness (check by test tiles). Replace some kaolin in the glaze recipe with calcined kaolin.

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Defect · Glaze firing

Crawling

Also called: glaze crawl, beading

Glaze pulls away from the surface of the piece, leaving bare clay islands or beading into pools.

Appears at: Glaze firing
Severity: Cosmetic
How common: Common

Causes

Most likely

·Greasy or dusty bisqueware surface when glaze was applied
·Glaze applied too thickly, particularly on a high-shrinkage recipe
·Glaze has excessive plastic clay, causing shrinkage on drying

Prevention

·Clean bisqueware with a damp sponge before glazing
·Apply glaze at recommended thickness (check by test tiles)
·Replace some kaolin in the glaze recipe with calcined kaolin

Can it be fixed?

·Fill crawled areas with the same glaze and refire

Materials involved

Glaze materials whose chemistry sits behind this defect — each links to its reference page.

Zinc oxide Tin oxide Zircopax Calcined kaolin CMC gum Bentonite

Questions

Why does crawling happen?: Most often: Greasy or dusty bisqueware surface when glaze was applied. Other causes: Glaze applied too thickly, particularly on a high-shrinkage recipe. Glaze has excessive plastic clay, causing shrinkage on drying..
Can crawling be fixed?: Sometimes. Fill crawled areas with the same glaze and refire.
How do I prevent crawling?: Clean bisqueware with a damp sponge before glazing. Apply glaze at recommended thickness (check by test tiles). Replace some kaolin in the glaze recipe with calcined kaolin.

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.

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