draftsmanship vs opus

draftsmanship

noun
  • the skill of drawing 

  • the art or craft of a draftsman 

opus

noun
  • A work, especially of art. 

  • A work of music or set of works with a specified rank in an ordering of a composer's complete published works. 

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