Lines of constant nucleation rate per H-nucleus according to the numerical fit to the experimental data. The red lines correspond to values of J/N_H from 10^-34 s^-1 (top) to 10^-10 (bottom) in steps of 10². The shaded area indicates the range of pressures typically encountered at the inner edge of dust shells. The thick dashed (blue) line corresponds to the critical nucleation rate of J/N_H = 10^-20 particles cm^-3 s^-1 where massive dust nucleation commences under circumstellar conditions. The uppermost (green) line corresponds to the stability limit if solid SiO is in equilibrium with a gas with standard cosmic elemental abundances. The line denoted as “wind” corresponds to the p-T-trajectory of a wind model. The circles correspond to the data points of the laboratory experiments, if the pressure of SiO in the condensation zone is converted into an equivalent pressure of a gas with cosmic elemental composition.