kaolin vs terracotta

kaolin

noun
  • A fine clay, rich in kaolinite, used in ceramics, paper-making, etc. 

terracotta

noun
  • A hard red-brown unglazed earthenware, used for pottery and building construction. 

  • A reddish brown colour, like that of terra cotta. 

adj
  • Of the colour of terracotta. 

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