Precise glass temperatures

Since the glass temperature T-g is a corresponding temperature for amorphous materials, if measured properly, precise values are needed. When determinations are made by cooling from equilibrium, material characterizing values are obtained. Most reported values are obtained in heating experiments which yield specimen-specific values, which approximate fictive temperatures T-f. Examples of consequent discrepancies of relaxation times at T-g are given. Results obtained in cooling show that it is likely that the mobility at T-g of local molecular motions is the same for all of the amorphous materials examined. In addition, it is shown that relatively precise values of T-g can be obtained from the recoverable compliance.