etching vs rotogravure

etching

noun
  • The image created by this process. 

  • The art of producing an image from a metal plate into which an image or text has been etched with acid. 

rotogravure

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

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

  • A print made by such a method. 

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