indenture vs mezzotint

indenture

verb
  • To indent; to make hollows, notches, or wrinkles in; to furrow. 

  • To bind a person under such a contract. 

noun
  • A contract which binds a person to work for another, under specified conditions, for a specified time (often as an apprentice). 

  • An indentation; a recess. 

  • A document, written as duplicates separated by indentations, specifying such a contract. 

mezzotint

verb
  • To make such etchings 

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. 

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