assoil vs harshen

assoil

verb
  • To make (something) dirty or soiled; to soil; to stain; to sully. 

  • Followed by from or of: to release or set free (someone) from a liability, an obligation, etc.; to discharge. 

harshen

verb
  • To make, or to become harsh; render hard and rough. 

  • To render peevish, morose, or austere. 

How often have the words assoil and harshen occurred in a corpus of books? (source: Google Ngram Viewer )