Jeff Zamek Ceramics Consulting Services

Glaze Defects - Causes and Corrections

As potters we have all been faced with a clay body defect either in the forming, drying, or firing stages when working with clay.  Sometimes it is difficult to determine if the clay body or the glaze caused the defect. While there are some types of defects that are unquestionably clay body related and some types of defects that are attributable to glazes, sometimes the defect is caused by the interaction between kiln firing/clay body and glaze. Clay and glaze defects can also be caused by any number of other miscalculations which can range from, choosing the wrong clay body or glaze formula for the firing temperature, inferior clay forming techniques and a general lack of knowledge on how ceramic materials react in their construction and firing stages. There are many possible clay body defects along with compound defects, which result in more than one type of defect on a pot or ceramic sculpture.

One of the most common defects is glaze crazing. While not technically a clay body defect it can be corrected through adjusting the clay body or glaze or both. Crazing is a fine network of lines in a fired glaze. When the clay body and glaze reach temperature in the kiln everything fits perfectly. At this point think of the glaze as a “honey” like viscosity on the rigid underlying clay body.