The Collaborative International Dictionary of English v.0.48:

Besmut \Be*smut"\, v. t. [imp. & p. p. Besmutted; p. pr. & vb.
   n. Besmutting.] [Pref. be- + smut: cf. AS. besm[imac]tan,
   and also OE. besmotren.]
   To blacken with smut; to foul with soot.
   [1913 Webster]