etching vs photoengraving

etching

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

  • The image created by this process. 

photoengraving

noun
  • A process of transferring a photographic image onto a plate which is then etched and printed. 

  • A plate or reproduction made using this process. 

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