Blisters are evident on the fired glaze surface as a 'moonscape'
of craters, some with sharp edges and others rounded. These
craters are the remnants of bubbles that have burst during final
approach to temperature or early stages of cooling. In some
cases there will be some unburst bubbles with a fragile 'dome'
than can be broken. Blisters can vary in size and tend to be
larger where the glaze is thicker. Is the glaze fluid enough?
Often glazes appear like the melt should have plenty of mobility
to heal but this can be deceptive, a melt flow testing regimen
is the only way to know for sure (melt flow testers have a
reservoir at the top of a steep incline and the glaze runs down
a calibrated runway). Generally a more fluid glaze will heal
blisters much better (see section below on blisters occurring
even after refire). Are excessive gases generated during glaze
fire? Significant amounts of gases can be generated within the
glaze itself due to the decomposition of some materials after
melting has started (i.e.