Answered By: Regan Brumagen
Last Updated: Nov 22, 2016     Views: 13

From Dr. Robert Brill, Research Scientist Emeritus:

In making glass ceramics, the objects are first fabricated from hot glass.  Then they are reheated to a temperature close to the softening point for some extended period of time.  The time and temperature are critical.  (The temperature required is also different for glasses having different chemical compositions.)  If the temperature is too high, the glass could deform and lose its shape.  If it is too cool, nothing special will happen.  If it is at just the right temperature, the atoms in the glass acquire sufficient mobility that some can move around a bit and rearrange themselves into a crystal lattice, that being the form that the laws of chemical thermodynamics would like them to be in.  Given enough time (and providing there are the right number and kinds of nuclei around which the crystals can form) the crystals grow.  When the material becomes 50% or more crystallized, it fits the definition of being a glass ceramic.