masterwork vs piece of junk

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. 

piece of junk

noun
  • A bad person or thing; an object of poor quality. 

  • Used other than figuratively or idiomatically: see piece, of, junk. 

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