With the advent of easy ceramic calculations perhaps you, like many others, have wanted to calculate the thermal expansion of clay bodies in order to predict the likelihood of fitting a selected glaze. Let's consider some of the problems with calculating the expansion of clay bodies with reliability.
Particles can be crystalline, glassy, or amorphous.
Thus each particle type responds individually to the amount of heat received during a firing. Some will melt and flow around others, strongly imparting the expansion characteristics of their new form to the matrix as a whole. Some will change from one mineral type into another of different expansion properties without melting. Others will remain unchanged acting as an aggregate, having only the peripheral edges of the particles dissolved somewhat by the melting of neighboring particles. Some will and unite with neighboring particles of similar type to form a glassy or crystalline network.