potter's clay vs terracotta

potter's clay

noun
  • The clay used by a potter. 

  • A person or people created and shaped by God. 

  • A nation or kingdom. 

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 potter's clay and terracotta occurred in a corpus of books? (source: Google Ngram Viewer )