mezzotint vs tracing

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 

tracing

noun
  • The reproduction of an image made by copying it through translucent paper. 

  • A record in the form of a graph made by a device such as a seismograph. 

  • The process of finding something that is lost by studying evidence. 

  • A regular path or track; a course. 

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