The EBCT test bars (engobe compatibility) in the foreground demonstrate the issue (they sandwich the engobe and body as a bi-clay strip). After firing at cone 10R they have curled toward the engobe side, indicating that it is shrinking more. On the mug the engobe has done likewise, shrinking more than the body and creating a crack pattern.
Pages that reference this post in the Digitalfire Reference Database:
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.