Effective extinction curves of face-on discs with an opening angle of 45°, computed for aCSi dust. The colours are again the same as in Fig. 6, with orange indicating N_cl = 1000, and proceeding through yellow, green and blue for N_cl = 2000,3000,5000 to magenta specifying N_cl = 10 000, with violet indicating a homogeneous disc. The feature at ~4–5μm^-1 does not change while the continuum scattering shows significant changes in the optical and UV.