Here is what happens when a glaze has too much raw clay

This is an example of how a glaze that contains too much plastic clay has been applied too thick. It shrinks and cracks during drying and is guaranteed to crawl. This is raw Alberta Slip. To solve this problem you need to tune a mix of raw and roasted clay. Enough raw clay is needed to suspend the slurry and dry it to a hard surface, but enough calcine is needed to keep the shrinkage low enough that this cracking does not happen. Perhaps you have been using a glaze having a high percentage of clay and this does not happen - the reason is likely that the clay is not highly plastic.

Related Pictures

G2934 cone 6 matte glaze + 5% Zircon is crawling

The crawling is happening at sharp concave surface contours (e.g. inside bottom corners on mugs) and on pieces like this. G2934 has good melt fluidity so that is not the issue. Here are some questions to consider:
-Did the glaze crack on drying? That is a sure sign it will crawl. Did you use calcined kaolin as specified in the recipe? That helps reduce the shrinkage as it dries (to eliminate the cracking).
-This looks like it is going on pretty thick - was it correctly mixed as a thixotropic slurry (high water content, 1.44 specific gravity, and gelled)? Or was it mixed with low water content (e.g. 1.55 specific gravity).
-These crawled areas were disturbed during spout forming, what can be done to repair the surface then?
-This is firing pretty glossy so kiln cooling is likely pretty fast. A drop and hold firing can help (as long as the glaze is not too thickly applied).
-Slower cooling means it will likely fire too matte, that is why we make an 80:20 blend of G2934 and G2926B glossy - to enable tuning matteness to any firing schedule.
-Mix up some of it as a brushing glaze. Apply a thin layer onto the bisque in the areas likely to crawl. Then dip the whole piece in the dipping glaze version.
-Mix the batch as a base coat dipping glaze, then it will adhere better to the bisque.
-Reduce the amount of calcined kaolin somewhat in favor of raw kaolin (perhaps 5%) - that may produce a slurry with better coverage and adherence.

Links

Media	Subsitute Gerstley Borate in Floating Blue Using Desktop Insight Use Desktop Insight to explore ways of calculating substitutes for Gerstley Borate in the popular Floating Blue cone 6 glaze recipe while maintaining or improving the other raw and fired properties of the glaze.
Glossary	Glaze Shrinkage Raw ceramic glazes contain clay to harden them on drying and to suspend the slurry. The more clay there is the more the glaze shrinks as it dries on the piece.
Glossary	Glaze thickness Many ceramic glaze benefits and issues are closely related to the thickness with which the glaze is applied. Many glazes are very sensitive to thickness, so control is needed.
Troubles	Powdering, Cracking and Settling Glazes Powdering and dusting glazes are difficult and a dust hazard. Shrinking and cracking glazes fall off and crawl. The cause is the wrong amount or type of clay.
Troubles	Crawling Ask yourself the right questions to figure out the real cause of a glaze crawling issue. Deal with the problem, not the symptoms.
Materials	Alberta Slip 1900F Calcined
Materials	Alberta Slip Albany Slip successor - a plastic clay that melts to dark brown glossy at cone 10R, with a frit addition it can also host a wide range of glazes at cone 6.

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