illustration vs mezzotint

illustration

noun
  • A picture designed to decorate a publication, or elucidate a literary work. 

  • A calculated prevision of insurance premiums and returns (life insurance) 

  • The state of being illustrated, or of being made clear and distinct. 

  • The act of illustrating; the act of making clear and distinct; 

  • Something which illustrates; a comparison or example intended to make clear or apprehensible, or to remove obscurity. 

mezzotint

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. 

verb
  • To make such etchings 

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