blacken vs harshen

blacken

verb
  • To make dirty. 

  • To defame or sully. 

  • To cook (meat or fish) by coating with pepper, etc., and quickly searing in a hot pan. 

  • To become black. 

  • To cause to be or become black. 

harshen

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

  • To render peevish, morose, or austere. 

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