monoprint vs photogravure

monoprint

verb
  • To print using this technique. 

noun
  • A form of printing on paper from a glass sheet to which oil paint has been applied; monotype. 

photogravure

verb
  • To print by this process. 

noun
  • An intaglio process for printing photographic reproductions in newspapers and books. 

  • A print so made. 

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