gravestone vs masterpiece

gravestone

noun
  • A stone slab set at the head of a grave. 

masterpiece

noun
  • A work created in order to qualify as a master craftsman and member of a guild. 

  • A piece of work that has been given much critical praise, especially one that is considered the greatest work of a person's career. 

  • A work of outstanding creativity, skill or workmanship. 

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