lithograph vs rotogravure

lithograph

noun
  • A printed image produced by lithography. 

verb
  • To create a copy of an image through lithography. 

rotogravure

noun
  • A printing process by which the paper is rolled through intaglio cylinders. 

  • A print made by such a method. 

  • A portion of a printed work produced by this method. 

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