This is crazing. Crazing is bad on functional ware.

Monday 1st January 2018

The left glaze is "stretched" on the clay so it cracks (it calculates to a high insight-live.com/glossary/18">thermal expansion so this is not a surprise). This usually appears after firing but can appear years later. When the lines are close together like this it is more serious. If the effect is intended, it is called "crackle" (but no one would intend this on functional ware). The one on the left calculates much lower - and stays uncrazed indefinitely. Potters, hobbyists and artists invariably bump into this issue whether using commercial glazes or making their own.

"Art language" solutions don't work, at least some technical words are needed to even understand what this simply is: A mismatch in the thermal expansions of glaze and body. Most ceramics expand slightly on heating and contract on cooling. Even though the amount of change is very small, ceramics are brittle so if a glaze is stretched on the ware, it will crack to relieve the stress. Crazing appears when ceramic is cooled and the glaze contracts more than the clay to which it is rigidly attached.

Pages that reference this post in the Digitalfire Reference Library:

Two matte mechanisms: One crazes the other does not, Glaze Chemistry, Glaze Crazing, Glaze Crazing

This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.