piece of work vs work of art

piece of work

noun
  • A product or manufactured article, especially an item of art or craft. 

  • A person who has a strong and unusual personality, especially one with seriously unpleasant character flaws (e.g. a nasty piece of work). (This sense came about due to Hamlet’s soliloquy (see sense 1 above)). 

work of art

noun
  • A product of the fine arts; a painting, sculpture, etc. 

  • Anything beautiful or exquisite. 

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