This recipe melts to such a fluid glass because of its high sodium and lithium content coupled with low silica levels. Reactive glazes like this produce interesting visuals but these come at a cost that is more than just the difficulty in firing. Recipes like this often calculate to an extremely high thermal expansion. That means that not only will this form a lake in the bottom of ware when used on the inside, but the food surfaces will craze badly. The low silica will also contribute to leaching of the lithium and any colorants present.
Ceramic glazes melt and flow according to their chemistry and mineralogy. Observing and measuring the nature and amount of flow is important in understanding them.
Ceramic glazes can leach heavy metals into food and drink. This subject is not complex, there are many things anyone can do to deal with this issue
Crazed ceramic glazes have a network of cracks. Understanding the causes is the most practical way to solve it. 95% of the time the solution is to adjust the thermal expansion of the glaze.
Glaze is excessively runny on firing
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