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.
Engobes are high-clay slurries that are applied to leather hard or dry ceramics and fire opaque. They are used for functional or decorative purposes.
|Tests||Engobe Body Compatibility Test|