brainchild vs masterwork

brainchild

noun
  • A creation, original idea, or innovation, usually used to indicate the originators 

verb
  • To think up; to come up with. 

masterwork

noun
  • A piece of quality, indicative of having been made by a master; a masterpiece. 

  • A piece done to prove possession of skill sufficient to be ranked a master. 

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