This is a simple and quick demonstration of the process oftempering of a solid, and the dramatic change in physical properties that can result.  (Adapted from a suggestion made by Marc Richard, Richard Stockton College.)

This demonstration could be used in the context of a unit on solid phase morphologies or materials chemistry.  But it could equally well be used (with an abbreviate explanation) to illustrate the formation of kinetic vs thermodynamic products by altering the means of fabrication.