halftone vs mezzotint

halftone

noun
  • A picture made by using the process of half-toning. 

  • An intermediate or middle tone in a painting, engraving, photograph, etc.; a middle tint, neither very dark nor very light. 

  • Synonym of semitone, half the interval between two notes on a scale. 

verb
  • To reproduce a photograph or other continuous tone image by the use of dots of various sizes. 

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 halftone and mezzotint occurred in a corpus of books? (source: Google Ngram Viewer )