Bloating is a serious issue that forms in the firing process. It results in blisters or warts on the clay surface; the glaze applied is not the issue, rather the clay itself, and the firing temperature.

Pinholes are another type of glaze defect that is usually related to the glaze itself rather than the clay body.

If you are experiencing pinholes in your glaze finishes, or have problems with clay bloating, the article below from Tony Hansen at Plainsman Clays is an in-depth look at both of these defects.

Pinhole and Bloating