Snapshots of the development of the convective front in model A, at t = 437 s (upper panel), 635 s (central panel), and 709 s (lower panel), shown in terms of the ²⁰Ne mass fraction, in logarithmic scale. Snapshots correspond to 2D slices on the xz plane, taken at y = 4 × 10⁷ cm. The dredge-up of fresh material from the outer core, driven by Kelvin-Helmholtz instabilities, translates into a mean metallicity in the envelope of 0.211, 0.234, and 0.241, respectively. The mean metallicity at the end of the simulation reaches 0.246, by mass, for this model.