Top panel: multi-epoch spectra for models r0e2 (smooth) and r0e2cl (clumped, with a uniform volume-filling factor of 10%; the quantity λF_λ is shown). With clumping, the spectra are much redder, with lines from ions of a lower ionization state (neutral or once ionized). Bottom panel: illustration of the line contributions for the most important ions in model r0e2cl at 63 d after explosion.