The observation of a deep minimum in the light curves of some novae, accompanied by a simultaneous rise in the infrared some weeks after outburst, is attributed to the rapid formation and growth of dust grains in the ejecta (Clayton & Wickramasinghe 1976). The observed nucleation rate J(obs) ~ 10−10 cm−3 s−1 for typical dusty novae, whereas the expected homogeneous nucleation rate J(hom) ~ 6 × 10−26 cm−3 s−1. We suggest that heterogeneous nucleation on ions could be a possible grain forming mechanism. In this case J(het) ~ 3.3 × 10−12 cm−3 s−1, which is within an order of magnitude of the observed nucleation rate.