Chink vs zipperhead

Chink

noun
  • A person of perceived Chinese ethnicity. 

adj
  • Chinese, or perceived to be Chinese. 

zipperhead

noun
  • A person of East Asian descent. 

  • A soldier in the Royal Canadian Armoured Corps or in the Armoured Crewman military trade. 

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