What Is Crazing in Ceramics?

Tension

• Glaze is used to keep moisture from penetrating the ceramic piece. When a glaze is under too much tension, crazing is the result. Tension happens because the glaze has contracted more than the ceramic piece when it cools. Glazes are thin coatings and as a result many will craze -- or pull apart -- with very little tension.

Immediate Crazing

• Crazing may be noticed immediately upon removing the ceramic piece from the kiln or very soon thereafter. The size of all ceramic pieces change during both the heating and cooling process. Expansion and shrinkage must match both the ceramic piece and the glaze in order to prevent crazing.

Delayed Crazing

• Delayed crazing can take weeks and sometimes even months to appear. Delayed crazing may be caused by under-firing. Under-firing can occur if there are variations in heating uniformity in the kiln, if the kiln is not properly adjusted and shuts off too soon, or if the controller thermocouple is inaccurate. Delayed crazing may also occur if too much moisture gets into the ceramic piece. With low-fire ceramic ware, it is best to hand wash the pieces rather than constantly putting the items in a dishwasher, according to American Ceramics.

Antique Crazing

• Crazing may appear In some antique pieces. This is not necessarily an indication of damage. According to the Antique Central website, in this case crazing is more likely due to the aging process and is the result of contraction and expansion due to humidity and temperature changes.

Consideration

• While proper firing, firing to the proper cone number, is extremely important to prevent crazing, today's lead-free formulas have less of a range for firing. According to Ceramic Arts, lead-free glazes reach their fired properties more quickly, making proper firing even more critical.