cheapen vs mezzotint

cheapen

verb
  • to make vulgar 

  • to become cheaper 

  • to decrease the value of; to make cheaper 

mezzotint

verb
  • To make such etchings 

noun
  • A form of intaglio etching in which a metal plate is roughened evenly and then smoothed to bring out an image. 

  • An etching or print made using this method. 

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