Frenkel's theory of liquid-phase sintering was interpreted regarding pores as the activated component. The data of isothermal sintering shrinkage vs. time of the cordierite glass by Giess et al. are trained using the model by Nikolic et al. to obtain the relative density at varied temperatures and time. Then, the time constants are obtained as 1998.86mins, 388.21mins, 89.79mins and 26.11mins at 800 degrees C, 820 degrees C, 840 degrees C and 860 degrees C, respectively. The calculated time constants are close to that by the theoretical calculation, deviation of which arises from the fact that particle size is variable during the sintering process. The time constant determination is crucial to the research of the whole sintering process.