Comparison of the optical spectrum of SN 1998S at 375 d (black) with synthetic spectra of the SN IIn model at 300 d endowed with different amounts of dust from zero to 0.001 M_⊙ (red). The observed spectrum has been corrected for redshift and reddening. The model spectra have been scaled to the adopted distance of 17 Mpc to SN 1998S. When included, the dust is chosen to be 0.1 μm silicate grains and located in the outer-ejecta dense shell.