caking vs mother-of-pearl

caking

noun
  • A layer or deposit of caked material. 

mother-of-pearl

noun
  • The hard pearly inner layer of certain mollusk shells; nacre. 

  • A butterfly of the genus Salamis. 

adj
  • Made from or looking like mother-of-pearl; iridescent or pearly. 

How often have the words caking and mother-of-pearl occurred in a corpus of books? (source: Google Ngram Viewer )