mezzotint vs stipple

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. 

stipple

verb
  • To use small dots to give the appearance of shading to. 

noun
  • The use of small dots that give the appearance of shading; the dots thus used. 

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