The evolution of the physical and dust properties of 1.5 M_⊙ and 2 M_⊙ stars during the AGB phase. Left: Time variation of the surface carbon mass fraction (solid lines, scale on the left) and of the total mass (dashed lines, scale on the right) of model stars with metallicity Z = 8 × 10⁻³ and initial masses (taken at the start of the core helium burning) of 1.5 M_⊙ (red lines) and 2 M_⊙ (black). The first part of the AGB evolution, during which the stars are oxygen-rich, is indicated with thin lines and the evolutionary phases after the C-star stage is reached with thick lines. Right: Time variation of solid carbon (dashed lines) and SiC (solid lines) production rates experienced by the 1.5 M_⊙ (triangles) and 2 M_⊙ (squares) model stars reported in the left panel during the C-star phase. The individual points refer to the inter-pulse phases. Magenta lines and points indicate the variation in the dust-to-gas ratio (scale on the right).