The mechanism of nucleation and crystal growth of hard gold (Au-Ni) on a gold rotating disc electrode from a proprietary bath (Renovel N) was investigated using linear sweep voltammetry and chronoamperometry. It was shown that two distinct mechanisms in two potential ranges are involved in this process. Experimental current-time transients at more positive potentials were described in terms of three-dimensional progressive nucleation and growth of right-circular cones. Time-independent inhibition of the vertical crystal growth was observed with an increase in negative potential, similar to the soft gold deposition. A modified inhibition model, in which vertical growth rate was assumed to decrease exponentially with time to a constant value, was derived to interpret experimental current-time transients recorded at more negative potentials. The chronoamperometric transients were well described by this model. Potential dependence of initial minima, maxima and final steady-state current was discussed.