We present a numerical study for the evolution of non-DA white dwarfs of 0.4, 0.55, 0.8, 1.0, and 1.2M ⊙. We pay special attention to the behaviour of the crystallization front. It is shown that crystallization begins at higher luminosities the higher the white dwarf mass is. The shape of the crystal growth function is very similar, almost independent of the value of the total stellar mass. We also study the crystallization process analytically, finding that it is nicely reproduced by a very simple model that accounts for the numerical results.