A crazing glaze cracks into islands because it has a higher contraction on cooling than the body. Clearly then, our challenge is to alter the expansion of the glaze. Almost any fired ceramic experiences expansion as it is heated and contraction as it is cooled. A typical piece of ware is a two-part system in that body and glaze possess independent expansion characteristics. However, a glaze is fixed to the underlying body and is therefore obliged to conform to the body's contraction during cooling in the kiln, and its later thermal induced size changes.
Stresses are thus part of any glaze-body 'marriage'.
We can use this stress to improve ware strength or we can let it ruin the ware. Let's consider these points separately now. This buffer forms as the liquid glaze phase attacks the body, dissolving it and forming intermediate compositions layered against the body. Intermediate zones also form within the body where diffusion of chemical species from the glaze penetrate into it. The temperature, soaking, cooling rate, glaze and body chemistry, and material particle sizes all affect the development of the intermediate zones.