Evolution of the Ca abundance stratification in our T_eff = 8500 K, log g = 4.0 atmospheric model, assuming a mass-loss rate of 3.8 10⁻¹³ solar mass per year (Z-loss = 8.36 10⁻¹⁵). The horizontal thick solid black line shows the abundance at t = 0 (homogeneous solar abundance), and the thick solid blue curve represents the final stationary solution (t = 7.93 10⁷ years). This is the same stratification as shown by the solid line in Fig. 4. The stratification at intermediate time steps is displayed with thin lines (grey, red, and blue), and a few of them are highlighted (thick green curves); the corresponding ages in years are listed within the drawing area (same colours as the corresponding curves). Three of the four green curves are tagged (1–3) to illustrate the development and subsequent expulsion of a Ca cloud. The dashed thick green line corresponds to the three stratification steps prior to stationarity (towards the end, the evolution slows down markedly).