What’s causing my fired glaze to be full of bubbles?

Bubbling in glazes can occur for a variety of reasons. It may be the result of some impurity (contamination) in the glaze burning away. For example, if the glaze surface has been ground down using an abrasive block or material to remove a fault and then refired. It may be the result of the natural bubbling which takes place during the firing. This normally is seen as a large number of small bubbles throughout the glaze layer, and is indicative of a ‘short firing’, meaning either too fast or too low in temperature. Ware affected by this fault can be refired to a slightly higher temperature or at least the same temperature with a longer soak period, and the fault should disappear. Large bubbles seen at the surface is the onset of blistering, i.e. the bubbles have not burst.