Crawling.

I checked in my copy of The Potter's Dictionary of Materials and Techniques by Hamer and Hamer this morning regarding the crawling problem.

This particular glaze I am using has 55% Gerstley Borate as an ingredient. Gerstley Borate is a variety of colemanite. H&H states that, "Colemanite encourages crawling by loosening the glaze layer during the firing prior to fusion. Colemanite contains water as part of its crystal structure. Decomposition between 1292 deg. F and 1472 deg. F liberates this water and the vapour loosens the glaze layer. When the glaze melts, it's surface tension pulls the glaze into separate areas leaving bare patches."

I am almost 100% sure this is the cause of my problem. So I will start running some tests with some glazes that get the boron from a frit instead of the Gerstley.

More fun.