  We present Monte Carlo line transfer models that investigate the effects of
dust on the very late time emission line spectra of the core collapse
supernovae SN 1980K and SN 1993J and the young core collapse supernova remnant
Cassiopeia A. Their blue-shifted emission peaks, resulting from the removal by
dust of redshifted photons emitted from the far sides of the remnants, and the
presence of extended red emission wings are used to constrain dust compositions
and radii and to determine the masses of dust in the remnants. We estimate dust
masses of between 0.08 - 0.15 M$_\odot$ for SN 1993J at year 16, 0.12 - 0.30
M$_\odot$ for SN 1980K at year 30 and $\sim$1.1 M$_\odot$ for Cas A at year
$\sim$330. Our models for the strong oxygen forbidden lines of Cas A require
the overall modelled profiles to be shifted to the red by between 700 - 1000 km
s$^{-1}$, consistent with previous estimates for the shift of the dynamical
centroid of this remnant.
