japan vs tooth enamel

japan

noun

  • A hard black enamel varnish containing asphalt. 

  • Lacquerware. 

verb

  • To varnish with japan. 

tooth enamel

noun

  • The hard, mineralised substance that makes up the visible part of teeth. 

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