Underglaze bubbling, where small bubbles or blisters appear on the surface of your ceramic piece after firing, can be attributed to a few different causes.
If there is residual moisture in the clay or underglaze, it can turn to steam during firing and create bubbles as it tries to escape. Proper drying before firing is essential to prevent this issue.
Firing underglaze at too high a temperature or too rapidly can also lead to bubbling. Rapid heating can cause gases to expand quickly and form bubbles on the surface.
Compatibility with Glaze
Using an incompatible glaze or firing underglaze and glaze at mismatched temperatures can create a barrier that traps gases and causes bubbling.
Applying underglaze unevenly or too thickly in certain areas can lead to variations in drying and firing, resulting in bubbles on the surface.
To prevent underglaze bubbling, ensure proper drying, follow recommended firing schedules, use compatible glazes, and apply underglaze consistently and evenly.