Crawling is a glaze fault where the melting glaze pulls back into beads or islands, leaving bare patches of clay. It usually starts before the firing, when the dried glaze coat cracks or doesn’t bond to the bisque.
What Is Crawling?
Digitalfire describes crawling as the molten glaze withdrawing into islands, and traces it mainly to problems that happen before the kiln. A glaze that shrinks too much as it dries cracks, and in the firing those cracks pull open into bare patches with rolled, rounded edges.
Common causes include glaze applied too thickly, especially in inside corners, dust or grease on the bisque, a second coat that re-wets and lifts the first, and glazes high in raw clay or materials that shrink. Firing glazed ware before it has dried can also cause it.
Prevention is usually simple: wipe bisque with a damp sponge, handle it with clean hands, apply thinner coats and let each layer dry. Some matte and specialty glazes are designed to crawl for a lichen-like texture, but on tableware unplanned crawling leaves bare clay that should be glazed over and refired. Before refiring, warm the piece and dab glaze onto the bare patches, since fresh glaze bonds poorly to glassy surfaces.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.