The incubation time for etch pit formation on single crystals of willemite was estimated for the first time by making successive optical measurements of the etch pit growth rate and then calculating incubation times by extrapolating the length vs. time curve for the etch pits back to zero width. Incubation times were estimated for the (0001) faces of willemite (containing minor impurities of Fe2+, Mg2+, and Al3+) after dissolution in acidic solutions (pH = 0–5) at 30°C. Shorter incubation times at lower pH were attributed to the pH dependence of leaching rates of the inhibitors (e.g., Fe2+), which in acidic solutions should accumulate rapidly at dislocation outcrops and maintain the near surface undersaturation of willemite, thus allowing etch pits to develop at these high energy sites. Dissolution (pH = 2) experiments with various cations (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Mg2+, Al3+, Fe3+) already present in the etchant indicated that incubation times were indeed related to the dissolution-inhibiting cations. Spiking of etchant (pH = 2) beyond a critical concentration of Fe2+ (0.01 M) significantly lowered the dissolution rates (especially along the < 2110 > and the < 101O >, i.e., normal to the sides of pit opening) and shortened the incubation time as measured by static immersion experiments.