japan vs topcoat

japan

noun
  • A hard black enamel varnish containing asphalt. 

  • Lacquerware. 

verb
  • To varnish with japan. 

topcoat

noun
  • A layer of paint or varnish etc. applied after the undercoat. 

  • A light overcoat. 

verb
  • To apply a topcoat to. 

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